Introduction to Chemistry Fundamentals

Let's study 9th standard ICICI chemistry Chapter 1, Language of Chemistry. The language of chemistry. In this chapter, we'll learn about many fundamental topics in chemistry. We use a lot of symbols in chemistry, especially while writing chemical reactions equations. A symbol is defined as something which represents a specific element. So we have 118 elements, and each has a unique symbol. So one symbol represents one atom of an element. For example, For example, S represents one atom of element sulfur. As you can see, there are a lot of cancellations here. Interestingly, earlier, symbols were in the diagrammatic or figurative form. And this method was discarded and Berzelius came up with the idea of using letters. Like this. You would notice that the letters are not in the form of letters. that many times the symbols are in Latin names. For example, silver is AG because that comes from Argentine. Why don't we use AR? Because that is already used for Argan. Next, let's talk about valency. It is defined as the combining capacity of an atom or radical, which is nothing but the number of hydrogen atoms which can combine with or displace one atom of the element or radical so as to form a compound. Let's take an example. If chlorine has to combine with hydrogen, the formula is HCl. So chlorine combines with one hydrogen atom, so its valency is 1. What about oxygen? It's H2O. So, So, oxygen's valency is 2 because it is combining with 2 hydrogen atoms. What about nitrogen? Ammonia. Here, nitrogen combines with 3 hydrogen atoms. So, valency of nitrogen is 3. Now, remember, the valency of metals as well as hydrogen is taken as a positive value. Whereas, the valency of non-metals or groups of non-metals called ions is taken as negative. But there is a simpler way to understand the concept of valency. It is simply the number of electrons. electrons lost or gained or shared during the formation of molecules or compounds. For example, potassium. Its atomic number is 19. What is its electronic configuration? 2,8,8,1. So, in order to be stable, what will it do? it would give away that last shell electron, one electron, the valence electron, to achieve the stable electronic configuration of the nearest noble gas, which in its case is argon, which is 2,8,8. Since it is giving away one electron, we say its valency is 1. And in an ionic bond, its charge would be plus 1. Because after giving an electron, it acquires a positive charge, it would have more protons and less electrons. You see, an atom is... is neutral because the number of protons and electrons are equal. That is the amount of positive charge and negative charge is equal. But after losing an electron, there is a deficiency of electron and metals hence acquire a positive charge. On the other hand, let's look at sulphur. Atomic number is 16, so electronic configuration is 2,8,6. So in order to be stable, that is acquire the electronic configuration of the nearest noble gas, that is complete its octet state, the last shell, it would gain 2 electrons. So then it becomes 2,8,6. So when it gains two electrons, it would become negatively charged. It will form an anion. That's right, nonmetals form anions. And its valency is 2. Now, by that logic, think about it and tell me what would be the valency of aluminium? Ready? The valency of aluminium is 3. Did you get it right? You see, aluminium would like to lose 3 electrons to become stable. But some elements have variable valency. For example, we can have copper 1 plus and even 2 plus. Or we can have iron 2 plus and even 3 plus. How does that work? Well, there is a good reason. This happens with the transition elements, by the way, in the periodic table. This does not happen with the first 20 elements. And this is because in these atoms, even the penultimate shell, that is the second last shell, is incomplete. Because they can lose electrons even from the second last shell. So, the octet and the duplicate rule does not happen. does not apply here but you will study this in detail in higher standards. Next what is the definition of radical? A radical is an atom or a group of atoms that behaves like a single unit and shows a valency. So you have to make some changes in definition. This is the correct definition, learn it word to word. A positive radical example is ammonium, a negative radical is hydroxide. So all these ions that you see, the positive ions with positive radicals and the negative ions, the anions. They are all radicals. By the way, we can have radicals without any charge as well, although it will have a valency. But we don't have that in our syllabus. So right now, you can just assume radicals to be the same as ions. But the truth is, they are not exactly the same thing. You have to learn all these valencies so that you can use this knowledge to form molecular formulae and solve sums. Subtitles by the Amara.org community Next, let's study about chemical formula. Definition, it's a molecule of a substance, that is, an element or a compound, which could be represented by its symbols. And the representation is known as chemical formula. Many cancellations here. Now let's understand how to use the crisscross method and the knowledge of all these valencies to form chemical formulae. First, the compound's name is ammonium carbonate. So ammonium, we write NH4 1+. It's ammonium, not ammonia, by the way. And carbonate. carbonate CO3 2-. You will remember these values if you learn this table very well. See here, carbonate anions are always on the right hand side here and ammonium is out here, NH4 1+. The signs won't be mentioned in the final answer. So this plus 1 goes to carbonate and the 2-goes to ammonium. So finally we have NH4 2 CO3 and the 1 need not be written, it's understood. But this 2 belongs to the entire ammonium ion. That is for nitrogen as well as for hydrogen. So put brackets out here. So this is the final answer. No signs required. Notice how this subscript was not affected at all. That remains as it is always. That doesn't shift or change. So in this molecule of ammonium carbonate, how many nitrogen atoms are present? Two. And how many hydrogen atoms are present? Four into two, eight. How many carbon atoms? One. And how many oxygen atoms? Three. Now, try to solve calcium dichromate. Notice how this these numbers can be cancelled so whenever you can reduce the numbers you should So now what is f is 1 and 1 so no need to write it so the final answer is this Next, what about platinic sulfite? If you notice, we have platinic, that is platinum 4, and we have platinous, that is platinum 2+. It's a variable valency, so you should remember them. And in the question, they will specify whether it is platinum 2 or platinum 4. That's a modern way of writing. And earlier, we used to use us and ick. Ick is always for a higher valency compared to us, which is for a lower valency. And sulfite is different from sulfate, which is different from sulfide. So be careful about these things and don't get confused. Even here, first we'll try to reduce the numbers if it's possible. Yes it is, two ones are and two twos are. So now this two comes down and the one comes down here. One we need not write, so I'll just write a Pt and sulfite SO3. And the 2 is for the entire ion, so I'll have to use brackets. But what about magnesium nitride? Well, just criss-cross. 3 comes here, 2 comes here. So that's Mg3. N2. No need for brackets because we have just a single elements out here. Here we have two elements combined together, sulfite. And the two number is for both of these elements. So we should not discriminate. We should put the brackets stating that the two number is for both of them. So that's how we'll solve a few sums in the exercise later. So often when two or more elements combine, they form something called a compound. Let's define it. It is a pure substance, just like an element. It is composed of two or more elements. And they are combined chemically in a fixed proportion, that is a fixed ratio. If they were not combined chemically, if they were physically combined, and if the ratio was not fixed, we wouldn't call it a compound, we would call it a mixture. For example, water is a compound. It has two elements, hydrogen and oxygen. They combine in a fixed proportion by weight, that is 2 ratio 1. And also the properties of water. of water are completely different from the properties of its constituent elements. Hydrogen is combustible. Oxygen supports combustion that is burning. Water is neither. A totally different substance is formed because of a chemical reaction. That's why it's a compound. It can be decomposed into simpler elements by some chemical method. But if you want to break down hydrogen further, that's not possible. And this orbital diagram even shows us how they are sharing electrons to achieve their stable electronic configuration. But that's not a part of this chapter. We'll study that in another chapter. So, what are the characteristics of compounds? Well, the components, that is the elements, are in a definite proportion. It is always homogeneous, it is a pure substance made up of only one kind of particle, that is molecule. They have a definite set of properties which are quite unique. And they don't retain the original properties. Also, they cannot be separated physically. They can be separated, the elements can be separated only chemically. Another example would be iron sulfide. What is this Roman number 2? Well that shows that this is Fe2+, ferrous. So it shows us the valency. You see iron has a variable valency. Fe3+, would be written as iron 3 sulfide, ferric sulfide. Notice how iron and sulfide chemically combine and they have totally different property now. Because iron sulfide cannot be attracted by magnet. And iron sulfide is not even soluble in carbon disulfide. Although sulfur could. Next, there is a list of compounds with their formulae. We need to learn these names. especially the acids. HCl seems like hydrogen chloride but when dissolved in water we call it hydrochloric acid. Nitric acid, sulfuric acid, carbonic acid which is a very unstable acid. It doesn't exist in this state. It decomposes to give carbon dioxide gas actually. But we need to remember this formulae and of course by looking at the formulae you can find out which elements are present in these compounds. In the names of the salts, you can often see the words dihydrate, pentahydrate. That's because blue vitriol is actually copper sulfate. But you see the dot 5H2O? Well, that's because there are five molecules of water of crystallization attached to it, due to which it's an... crystal form, blue colour, and hence we call it blue vitriol pentahydrate because every molecule of copper sulphate is surrounded by five molecules of water. And this dot represents a weak chemical bond. If you heat this, this water will evaporate and all you'll get is white powder of copper sulphate. And then we can't call it blue vitriol. So again, you'll study these properties of water crystallisation in detail in another chapter. This shows us the crisscross method which I have already taught you. Now there are some rules in naming certain chemical compounds. For example, if there is a salt, a compound between a metal and a non-metal. Metal is always written first and the non-metal will have iodine. For example, potassium plus iodine, potassium iodide. Next rule, if there are two non-metals combining, then you may need to use prefixes like mono, di, tri. For example, N2O is di-nitrogen oxide because there are two atoms of nitrogen combining with one atom of oxygen. The nitrogen oxide is di-nitrogen oxide. monoxide specifying that there is only one oxygen here by the way this is also called nitric oxide nitric oxide dinitrogen trioxide nitrogen dioxide which is reddish brown in color and dinitrogen pentoxide and so on another rule what if there are two elements and there is oxygen as well well if there is one with more oxygen then we use the suffix eight in the end and one compound which has less oxygen use ite. For example, potassium chlorate will have more of oxygen comparatively and potassium chlorite will have less of oxygen. Otherwise, the elements are same in both. As far as KClO is concerned, well, that has very less oxygen. So, we will use hypochlorite. And for excessive oxygen atoms in the compound, we use perchlorate. Then there are various examples which are all cancelled. We don't have to learn them. We can derive them with the help of the knowledge of the table. Next, chemical equations, definition. A chemical equation is a shorthand form for a chemical change. That is, we can show a chemical change as symbols and formulae like this. we get so much information from this equation you see, on the left hand side we have the reactants and on the right hand side we have the products and to represent them, we use symbols and formulae we don't write the names, if you write the names ammonium hydroxide plus hydrochloric acid gives ammonium chloride plus water That is called a word equation, not a chemical equation. So reactants and products definitions are also mentioned. Now there are some examples of chemical equations which we need to remember. What if you are asked to write any equation with one reactant and two or three products? It's a decomposition type of reaction. Well, any example would do as long as it is correct. You can learn this one, the decomposition of lead nitrate. This is something special. This equation will be repeated in many chapters. And a crackling sound is heard in this reaction, when this reaction takes place. What about an example of an equation with two reactants and one product? A kind of a combination reaction. So ammonia and water combine to form ammonium hydroxide. I show this reversibility sign because it's a reversible reaction. You see the ammonium hydroxide can also split back into the original reactants. Next, an example of two reactants and two products. It's a displacement reaction here. and two reactants and three or four products? Well, I would suggest you to use a simpler example to learn. Copper plus sulfuric acid gives copper sulfate plus water plus sulfur dioxide. Now remember that whenever you write an equation in exam, it has to be balanced. So you can see the coefficient 2 out here and the coefficient 2 out here in the beginning of the molecular formula. That is to balance the equation so that we make sure the number of atoms of each element on the left-hand side is equal to the number of atoms of each element on the right-hand side. This is done to comply with the law of conservation of matter. We will study how to balance equations shortly. Now there is a lot of information we get from a chemical reaction. like the reactants, products, whether it is irreversible or reversible. We can even mention in brackets below the compound to state their nature, like is it dilute or concentrated? Dilute means with a lot of water and concentrated means with less water. We can even state S, which means solid. or G which means gas and even L which means liquid or we can use AQ for aqueous. But there are some limitations in these equations. They don't tell us about the speed of reaction, whether it is a... fast reaction or a slow one. They don't tell us about any changes in color. For example, I told you that nitrogen dioxide is reddish brown gas, but that was not mentioned in the equation. We can't even know if the reaction will complete. That is, will all the reactants be utilized and completed to form the products? And we can't even show the evolution of light or sound energy. We can show the evolution of heat energy. We can just do the plus delta sign, plus triangle, which means heat is being produced. It's an exothermic reaction. But if energy is in the form of light, it's not going to be used. light and sound, we can't really show it. So these are the limitations. Now, what is a balanced equation? The definition is, as you rightly guessed, the number of atoms of each element is same on the reactants and the products side. If it was not balanced, just imagine if the number of oxygen atoms on these reactants side is different from the number of atoms of oxygen here, then you will start wondering, from where did these extra atoms come? Or where are the missing oxygen atoms? Well, that would be against the law of conservation of matter. And then... In a chemical reaction, matter can neither be created nor destroyed. Atoms cannot be created or destroyed in chemical reaction. By the way, in nuclear reaction, it does happen. But here we are talking about chemical reaction. So in order to comply with the law of conservation of matter, we will balance it. Here they have shown how to do that. But we'll study it when we do the sums in the exercise. There is a partial equation method which is not in syllabus at all. Next, let's understand the definition of relative atomic mass and relative molecular mass. Also called as atomic weight and molecular weight respectively. In physics... mass and weight have different meanings. You see, weight depends on gravity and mass doesn't. But in chemistry, we can use these terms interchangeably. First of all, consider these atoms. This is a hydrogen atom. Its atomic number is 1 because it has only one proton. And its mass number is also 1 because it has only one nucleon. That is, the number of protons plus neutrons is 1. In fact, it doesn't have any neutrons. The number of electrons doesn't affect the atomic number or the mass number. Although, the number of electrons will always be equal to the number of neutrons. number of protons in an atom. Let's take another atom, let's say beryllium. Its atomic number is 4. So it has 4 protons and interestingly it has 4 neutrons as well. It's not necessary that the number of neutrons have to be equal to the number of protons but here they are. So what is the atomic number? 4. It's the fourth element in the periodic table. And what is the atomic weight or atomic mass? Well, it's 4 plus 4, 8. And for carbon, Its atomic number is 6 and atomic mass or atomic weight is 12 because it has 6 protons and 6 neutrons. So looking at these diagrams, it's very easy to identify the atomic number and the atomic weight. Atomic weight or atomic mass is simply the sum of the number of protons and number of neutrons in the nucleus. Together they are called nucleons. But when we talk about the relative atomic mass, that is atomic weight, it's not so simple to calculate it. What we do is, first we consider the mass of a standard atom, and we have chosen, or rather scientists have chosen, the carbon atom as a standard. So what is the relative atomic mass or atomic weight of a carbon atom? It's 12, isn't it? It's 12. mu that is atomic mass unit but nowadays we call it dalton next we take 1 12th of it so what is 1 12th of the mass of a carbon atom yes it is one And now tell me, how many times is beryllium atom heavier compared to the number 1? That is, how many times is 8 compared to 1? Well, it is 8 times. Or simply speaking, the beryllium atom's mass is 8 times 1 twelfth the mass of a carbon-12 atom. By the way, we are not even counting the mass of the electrons because their mass is so small. Approximately 1,800 electrons mass is equal to the mass of one proton. So we just focus on protons and neutrons, which have almost the same mass. So when you ask me the atomic weight of beryllium, I can just look at this and I can tell you it's 8. That is 4 plus 4. But in reality, the scientific definition of atomic weight or atomic mass, relative atomic mass is the number of times one atom of an element is heavier than 1 12th the mass of a carbon-12 atom. We have to mention carbon-12 because Because in nature we have carbon-13 and carbon-14 also, that's right. Isotopes are possible. There are some carbon atoms which can have 7 neutrons or 8 neutrons. That won't change the atomic number. Of course, it will remain 6. That is the fundamental identity of a carbon atom. That won't change. But the mass number need not be fixed. It can sometimes be 13 or 14. So now let me ask you a question. Let me give you an oxygen atom. Atomic number is 8. And if I say that the oxygen atom is 16 times heavier, than 1 twelfth the mass of a carbon-12 atom. Then what is its relative atomic mass? Well, no wonder it is exactly 16. And an easy way to remember this is in an oxygen atom it has 8 protons and 8 neutrons. But again, you know, this is just an approximate number. The actual atomic weight of oxygen is 15.99. So the values we learn at school level are all integers, no decimal values. And we learn an easy way to learn the atomic mass, the number of... of protons plus neutrons. But if we use this definition, and scientists use a definition to calculate the values, we get a more accurate answer, 15.99. But fortunately, we just have learned the definition. We don't have any calculations regarding this. Now, similarly, we can calculate the relative molecular mass. mass of any molecule using the same definition. Now an easier way to calculate the relative molecular mass of water is, well it has two atoms of hydrogen plus one atom of oxygen. Hydrogen's atomic weight or atomic mass is one and oxygen's is sixteen. So this comes up to be totally eighteen atomic mass units. That's the relative molecular mass of water. But as far as the scientific definition is concerned, we would say that one molecule molecule of water is 18 times heavier than 1 12th the mass of a carbon 12 atom that is the standard scientific definition apart from the definition we need not know anything more about the scientific definition as far as numericals are concerned we won't even use this formula we will use our normal method only which is far easier and then we have a lot of cancellations now i have a challenging question for you if you look at the periodic table or even if you google it you will know notice that chlorine's atomic number is 17 and its mass number is 35.5, which is very strange. Mass number is approximately the total number of protons and neutrons. How can we have a decimal value for it? Well, if you can find the answer, leave it in the comments. Hi students, this is AJ sir. If you like this video, press the like button. If you would like to enroll for my online test series or online lectures, email me or message me on Instagram. Check the description for more information.

A symbol is defined as something which represents a specific element. So we have 118 elements, and each has a unique symbol. So one symbol represents one atom of an element.

For example, For example, S represents one atom of element sulfur. As you can see, there are a lot of cancellations here. Interestingly, earlier, symbols were in the diagrammatic or figurative form. And this method was discarded and Berzelius came up with the idea of using letters.

Like this. You would notice that the letters are not in the form of letters. that many times the symbols are in Latin names. For example, silver is AG because that comes from Argentine.

Why don't we use AR? Because that is already used for Argan. Next, let's talk about valency. It is defined as the combining capacity of an atom or radical, which is nothing but the number of hydrogen atoms which can combine with or displace one atom of the element or radical so as to form a compound. Let's take an example.

If chlorine has to combine with hydrogen, the formula is HCl. So chlorine combines with one hydrogen atom, so its valency is 1. What about oxygen? It's H2O.

So, So, oxygen's valency is 2 because it is combining with 2 hydrogen atoms. What about nitrogen? Ammonia. Here, nitrogen combines with 3 hydrogen atoms.

So, valency of nitrogen is 3. Now, remember, the valency of metals as well as hydrogen is taken as a positive value. Whereas, the valency of non-metals or groups of non-metals called ions is taken as negative. But there is a simpler way to understand the concept of valency.

It is simply the number of electrons. electrons lost or gained or shared during the formation of molecules or compounds. For example, potassium. Its atomic number is 19. What is its electronic configuration? 2,8,8,1.

So, in order to be stable, what will it do? it would give away that last shell electron, one electron, the valence electron, to achieve the stable electronic configuration of the nearest noble gas, which in its case is argon, which is 2,8,8. Since it is giving away one electron, we say its valency is 1. And in an ionic bond, its charge would be plus 1. Because after giving an electron, it acquires a positive charge, it would have more protons and less electrons. You see, an atom is...

is neutral because the number of protons and electrons are equal. That is the amount of positive charge and negative charge is equal. But after losing an electron, there is a deficiency of electron and metals hence acquire a positive charge. On the other hand, let's look at sulphur. Atomic number is 16, so electronic configuration is 2,8,6.

So in order to be stable, that is acquire the electronic configuration of the nearest noble gas, that is complete its octet state, the last shell, it would gain 2 electrons. So then it becomes 2,8,6. So when it gains two electrons, it would become negatively charged.

It will form an anion. That's right, nonmetals form anions. And its valency is 2. Now, by that logic, think about it and tell me what would be the valency of aluminium?

Ready? The valency of aluminium is 3. Did you get it right? You see, aluminium would like to lose 3 electrons to become stable.

But some elements have variable valency. For example, we can have copper 1 plus and even 2 plus. Or we can have iron 2 plus and even 3 plus. How does that work? Well, there is a good reason.

This happens with the transition elements, by the way, in the periodic table. This does not happen with the first 20 elements. And this is because in these atoms, even the penultimate shell, that is the second last shell, is incomplete.

Because they can lose electrons even from the second last shell. So, the octet and the duplicate rule does not happen. does not apply here but you will study this in detail in higher standards.

Next what is the definition of radical? A radical is an atom or a group of atoms that behaves like a single unit and shows a valency. So you have to make some changes in definition.

This is the correct definition, learn it word to word. A positive radical example is ammonium, a negative radical is hydroxide. So all these ions that you see, the positive ions with positive radicals and the negative ions, the anions. They are all radicals.

By the way, we can have radicals without any charge as well, although it will have a valency. But we don't have that in our syllabus. So right now, you can just assume radicals to be the same as ions.

But the truth is, they are not exactly the same thing. You have to learn all these valencies so that you can use this knowledge to form molecular formulae and solve sums. Subtitles by the Amara.org community Next, let's study about chemical formula. Definition, it's a molecule of a substance, that is, an element or a compound, which could be represented by its symbols.

And the representation is known as chemical formula. Many cancellations here. Now let's understand how to use the crisscross method and the knowledge of all these valencies to form chemical formulae.

First, the compound's name is ammonium carbonate. So ammonium, we write NH4 1+. It's ammonium, not ammonia, by the way.

And carbonate. carbonate CO3 2-. You will remember these values if you learn this table very well. See here, carbonate anions are always on the right hand side here and ammonium is out here, NH4 1+. The signs won't be mentioned in the final answer.

So this plus 1 goes to carbonate and the 2-goes to ammonium. So finally we have NH4 2 CO3 and the 1 need not be written, it's understood. But this 2 belongs to the entire ammonium ion.

That is for nitrogen as well as for hydrogen. So put brackets out here. So this is the final answer.

No signs required. Notice how this subscript was not affected at all. That remains as it is always.

That doesn't shift or change. So in this molecule of ammonium carbonate, how many nitrogen atoms are present? Two.

And how many hydrogen atoms are present? Four into two, eight. How many carbon atoms? One.

And how many oxygen atoms? Three. Now, try to solve calcium dichromate.

Notice how this these numbers can be cancelled so whenever you can reduce the numbers you should So now what is f is 1 and 1 so no need to write it so the final answer is this Next, what about platinic sulfite? If you notice, we have platinic, that is platinum 4, and we have platinous, that is platinum 2+. It's a variable valency, so you should remember them.

And in the question, they will specify whether it is platinum 2 or platinum 4. That's a modern way of writing. And earlier, we used to use us and ick. Ick is always for a higher valency compared to us, which is for a lower valency.

And sulfite is different from sulfate, which is different from sulfide. So be careful about these things and don't get confused. Even here, first we'll try to reduce the numbers if it's possible. Yes it is, two ones are and two twos are. So now this two comes down and the one comes down here.

One we need not write, so I'll just write a Pt and sulfite SO3. And the 2 is for the entire ion, so I'll have to use brackets. But what about magnesium nitride? Well, just criss-cross.

3 comes here, 2 comes here. So that's Mg3. N2.

No need for brackets because we have just a single elements out here. Here we have two elements combined together, sulfite. And the two number is for both of these elements.

So we should not discriminate. We should put the brackets stating that the two number is for both of them. So that's how we'll solve a few sums in the exercise later. So often when two or more elements combine, they form something called a compound. Let's define it.

It is a pure substance, just like an element. It is composed of two or more elements. And they are combined chemically in a fixed proportion, that is a fixed ratio. If they were not combined chemically, if they were physically combined, and if the ratio was not fixed, we wouldn't call it a compound, we would call it a mixture.

For example, water is a compound. It has two elements, hydrogen and oxygen. They combine in a fixed proportion by weight, that is 2 ratio 1. And also the properties of water.

of water are completely different from the properties of its constituent elements. Hydrogen is combustible. Oxygen supports combustion that is burning. Water is neither. A totally different substance is formed because of a chemical reaction.

That's why it's a compound. It can be decomposed into simpler elements by some chemical method. But if you want to break down hydrogen further, that's not possible.

And this orbital diagram even shows us how they are sharing electrons to achieve their stable electronic configuration. But that's not a part of this chapter. We'll study that in another chapter. So, what are the characteristics of compounds? Well, the components, that is the elements, are in a definite proportion.

It is always homogeneous, it is a pure substance made up of only one kind of particle, that is molecule. They have a definite set of properties which are quite unique. And they don't retain the original properties. Also, they cannot be separated physically.

They can be separated, the elements can be separated only chemically. Another example would be iron sulfide. What is this Roman number 2?

Well that shows that this is Fe2+, ferrous. So it shows us the valency. You see iron has a variable valency. Fe3+, would be written as iron 3 sulfide, ferric sulfide. Notice how iron and sulfide chemically combine and they have totally different property now.

Because iron sulfide cannot be attracted by magnet. And iron sulfide is not even soluble in carbon disulfide. Although sulfur could.

Next, there is a list of compounds with their formulae. We need to learn these names. especially the acids.

HCl seems like hydrogen chloride but when dissolved in water we call it hydrochloric acid. Nitric acid, sulfuric acid, carbonic acid which is a very unstable acid. It doesn't exist in this state.

It decomposes to give carbon dioxide gas actually. But we need to remember this formulae and of course by looking at the formulae you can find out which elements are present in these compounds. In the names of the salts, you can often see the words dihydrate, pentahydrate.

That's because blue vitriol is actually copper sulfate. But you see the dot 5H2O? Well, that's because there are five molecules of water of crystallization attached to it, due to which it's an...

crystal form, blue colour, and hence we call it blue vitriol pentahydrate because every molecule of copper sulphate is surrounded by five molecules of water. And this dot represents a weak chemical bond. If you heat this, this water will evaporate and all you'll get is white powder of copper sulphate.

And then we can't call it blue vitriol. So again, you'll study these properties of water crystallisation in detail in another chapter. This shows us the crisscross method which I have already taught you. Now there are some rules in naming certain chemical compounds.

For example, if there is a salt, a compound between a metal and a non-metal. Metal is always written first and the non-metal will have iodine. For example, potassium plus iodine, potassium iodide.

Next rule, if there are two non-metals combining, then you may need to use prefixes like mono, di, tri. For example, N2O is di-nitrogen oxide because there are two atoms of nitrogen combining with one atom of oxygen. The nitrogen oxide is di-nitrogen oxide.

monoxide specifying that there is only one oxygen here by the way this is also called nitric oxide nitric oxide dinitrogen trioxide nitrogen dioxide which is reddish brown in color and dinitrogen pentoxide and so on another rule what if there are two elements and there is oxygen as well well if there is one with more oxygen then we use the suffix eight in the end and one compound which has less oxygen use ite. For example, potassium chlorate will have more of oxygen comparatively and potassium chlorite will have less of oxygen. Otherwise, the elements are same in both. As far as KClO is concerned, well, that has very less oxygen. So, we will use hypochlorite.

And for excessive oxygen atoms in the compound, we use perchlorate. Then there are various examples which are all cancelled. We don't have to learn them.

We can derive them with the help of the knowledge of the table. Next, chemical equations, definition. A chemical equation is a shorthand form for a chemical change. That is, we can show a chemical change as symbols and formulae like this. we get so much information from this equation you see, on the left hand side we have the reactants and on the right hand side we have the products and to represent them, we use symbols and formulae we don't write the names, if you write the names ammonium hydroxide plus hydrochloric acid gives ammonium chloride plus water That is called a word equation, not a chemical equation.

So reactants and products definitions are also mentioned. Now there are some examples of chemical equations which we need to remember. What if you are asked to write any equation with one reactant and two or three products?

It's a decomposition type of reaction. Well, any example would do as long as it is correct. You can learn this one, the decomposition of lead nitrate.

This is something special. This equation will be repeated in many chapters. And a crackling sound is heard in this reaction, when this reaction takes place. What about an example of an equation with two reactants and one product? A kind of a combination reaction.

So ammonia and water combine to form ammonium hydroxide. I show this reversibility sign because it's a reversible reaction. You see the ammonium hydroxide can also split back into the original reactants. Next, an example of two reactants and two products. It's a displacement reaction here.

and two reactants and three or four products? Well, I would suggest you to use a simpler example to learn. Copper plus sulfuric acid gives copper sulfate plus water plus sulfur dioxide. Now remember that whenever you write an equation in exam, it has to be balanced. So you can see the coefficient 2 out here and the coefficient 2 out here in the beginning of the molecular formula.

That is to balance the equation so that we make sure the number of atoms of each element on the left-hand side is equal to the number of atoms of each element on the right-hand side. This is done to comply with the law of conservation of matter. We will study how to balance equations shortly. Now there is a lot of information we get from a chemical reaction.

like the reactants, products, whether it is irreversible or reversible. We can even mention in brackets below the compound to state their nature, like is it dilute or concentrated? Dilute means with a lot of water and concentrated means with less water.

We can even state S, which means solid. or G which means gas and even L which means liquid or we can use AQ for aqueous. But there are some limitations in these equations. They don't tell us about the speed of reaction, whether it is a...

fast reaction or a slow one. They don't tell us about any changes in color. For example, I told you that nitrogen dioxide is reddish brown gas, but that was not mentioned in the equation.

We can't even know if the reaction will complete. That is, will all the reactants be utilized and completed to form the products? And we can't even show the evolution of light or sound energy. We can show the evolution of heat energy.

We can just do the plus delta sign, plus triangle, which means heat is being produced. It's an exothermic reaction. But if energy is in the form of light, it's not going to be used.

light and sound, we can't really show it. So these are the limitations. Now, what is a balanced equation?

The definition is, as you rightly guessed, the number of atoms of each element is same on the reactants and the products side. If it was not balanced, just imagine if the number of oxygen atoms on these reactants side is different from the number of atoms of oxygen here, then you will start wondering, from where did these extra atoms come? Or where are the missing oxygen atoms?

Well, that would be against the law of conservation of matter. And then... In a chemical reaction, matter can neither be created nor destroyed.

Atoms cannot be created or destroyed in chemical reaction. By the way, in nuclear reaction, it does happen. But here we are talking about chemical reaction. So in order to comply with the law of conservation of matter, we will balance it.

Here they have shown how to do that. But we'll study it when we do the sums in the exercise. There is a partial equation method which is not in syllabus at all. Next, let's understand the definition of relative atomic mass and relative molecular mass.

Also called as atomic weight and molecular weight respectively. In physics... mass and weight have different meanings. You see, weight depends on gravity and mass doesn't. But in chemistry, we can use these terms interchangeably.

First of all, consider these atoms. This is a hydrogen atom. Its atomic number is 1 because it has only one proton.

And its mass number is also 1 because it has only one nucleon. That is, the number of protons plus neutrons is 1. In fact, it doesn't have any neutrons. The number of electrons doesn't affect the atomic number or the mass number. Although, the number of electrons will always be equal to the number of neutrons. number of protons in an atom.

Let's take another atom, let's say beryllium. Its atomic number is 4. So it has 4 protons and interestingly it has 4 neutrons as well. It's not necessary that the number of neutrons have to be equal to the number of protons but here they are.

So what is the atomic number? 4. It's the fourth element in the periodic table. And what is the atomic weight or atomic mass?

Well, it's 4 plus 4, 8. And for carbon, Its atomic number is 6 and atomic mass or atomic weight is 12 because it has 6 protons and 6 neutrons. So looking at these diagrams, it's very easy to identify the atomic number and the atomic weight. Atomic weight or atomic mass is simply the sum of the number of protons and number of neutrons in the nucleus.

Together they are called nucleons. But when we talk about the relative atomic mass, that is atomic weight, it's not so simple to calculate it. What we do is, first we consider the mass of a standard atom, and we have chosen, or rather scientists have chosen, the carbon atom as a standard. So what is the relative atomic mass or atomic weight of a carbon atom?

It's 12, isn't it? It's 12. mu that is atomic mass unit but nowadays we call it dalton next we take 1 12th of it so what is 1 12th of the mass of a carbon atom yes it is one And now tell me, how many times is beryllium atom heavier compared to the number 1? That is, how many times is 8 compared to 1? Well, it is 8 times. Or simply speaking, the beryllium atom's mass is 8 times 1 twelfth the mass of a carbon-12 atom.

By the way, we are not even counting the mass of the electrons because their mass is so small. Approximately 1,800 electrons mass is equal to the mass of one proton. So we just focus on protons and neutrons, which have almost the same mass.

So when you ask me the atomic weight of beryllium, I can just look at this and I can tell you it's 8. That is 4 plus 4. But in reality, the scientific definition of atomic weight or atomic mass, relative atomic mass is the number of times one atom of an element is heavier than 1 12th the mass of a carbon-12 atom. We have to mention carbon-12 because Because in nature we have carbon-13 and carbon-14 also, that's right. Isotopes are possible.

There are some carbon atoms which can have 7 neutrons or 8 neutrons. That won't change the atomic number. Of course, it will remain 6. That is the fundamental identity of a carbon atom. That won't change.

But the mass number need not be fixed. It can sometimes be 13 or 14. So now let me ask you a question. Let me give you an oxygen atom.

Atomic number is 8. And if I say that the oxygen atom is 16 times heavier, than 1 twelfth the mass of a carbon-12 atom. Then what is its relative atomic mass? Well, no wonder it is exactly 16. And an easy way to remember this is in an oxygen atom it has 8 protons and 8 neutrons. But again, you know, this is just an approximate number. The actual atomic weight of oxygen is 15.99.

So the values we learn at school level are all integers, no decimal values. And we learn an easy way to learn the atomic mass, the number of... of protons plus neutrons.

But if we use this definition, and scientists use a definition to calculate the values, we get a more accurate answer, 15.99. But fortunately, we just have learned the definition. We don't have any calculations regarding this.

Now, similarly, we can calculate the relative molecular mass. mass of any molecule using the same definition. Now an easier way to calculate the relative molecular mass of water is, well it has two atoms of hydrogen plus one atom of oxygen. Hydrogen's atomic weight or atomic mass is one and oxygen's is sixteen. So this comes up to be totally eighteen atomic mass units.

That's the relative molecular mass of water. But as far as the scientific definition is concerned, we would say that one molecule molecule of water is 18 times heavier than 1 12th the mass of a carbon 12 atom that is the standard scientific definition apart from the definition we need not know anything more about the scientific definition as far as numericals are concerned we won't even use this formula we will use our normal method only which is far easier and then we have a lot of cancellations now i have a challenging question for you if you look at the periodic table or even if you google it you will know notice that chlorine's atomic number is 17 and its mass number is 35.5, which is very strange. Mass number is approximately the total number of protons and neutrons. How can we have a decimal value for it?

Well, if you can find the answer, leave it in the comments. Hi students, this is AJ sir. If you like this video, press the like button. If you would like to enroll for my online test series or online lectures, email me or message me on Instagram. Check the description for more information.

Transcript for:Introduction to Chemistry Fundamentals

Transcript for:
Introduction to Chemistry Fundamentals