welcome to another episode of Terry's notes today we are going to be looking at the periodic table and periodicity the modern periodic table is a chart containing the elements arranged in order of increasing atomic number so this is how the periodic table is currently arranged in terms of increasing atomic number a vertical column called a group contains elements with similar properties so the vertical columns are called groups and they usually have similar chemical properties a horizontal row is called a period the atomic number of the elements in a period increased from left to right along the row before the periodic table was created several attempts were made to classify the elements into a useful way dorina arrang groups of tre elements with similar properties into Triads example lithium sodium and potassium had similar properties Mel arrang the elements in order of atomic number and what he did he left gaps for elements that weren't discovered as yet he could predict the properties of those undiscovered elements this this is just a uh sample of what Mel's periodic table look like and if you would notice he left gaps for elements that had not been discovered as yet but he can predict the physical properties or the chemical properties of these missing elements this gives this diagram gives um the current periodic table and we have groups which are these the groups are the vertical columns so this is group one this is group two and we continue going to the right so we have up to group seven on the side and the last group is called group zero or some sometimes group eight and the horizontal rows are what we call periods so these are groups and these are called p periods the elements in the periodic table are arranged in terms of atomic number as indicated earlier the horizontal rows of elements are called periods and vertical Columns of elements are called groups now let us look at some Trends in some of these groups we're going to be looking at group two group two elements have atoms with two electrons in the outermost occupied shell okay and these are the elements in group two bellium magnesium calcium strontium berium and these are the electronic configurations of each of these elements and if you will notice you will see that the last shell of each of them contains two electrons so the last shell will tell you which group The Element belongs to the group two elements are called the alkaline earth metals as the group is descended the atomic radi increases what this means is that as you go down the group the size of the atom increases the veent shell electrons or the outermost shell cell move further away from the nucleus and are therefore held less tightly so remember in an atom you have the nucleus and then we're going to have electrons so we have electrons here the nucleus is positively charged and electrons are negatively charged As you move down the group the size of the atom gets bigger and bigger right and therefore remember the nucleus is what is attracting electrons so if the electrons are moving further and further away from the nucleus it means that that they're being held less tightly the ease of ionization increases down the group ionization is a process of losing an outershell electron so therefore as you go down the group the outer shell electrons are lost more readily and that explains why the reactivity increases down the group so reactivity with oxygen water and hydrochloric acid increases down the [Music] group let us look at the reaction with water so the example we'll use is magnesium so clean magnesium reacts with cold water to produce magnesium hydroxide and hydrogen gas so mg + 2 H2O produces mg o taken twice plus H2 now you get a different reaction when magnesium reacts with steam what you get this time is magnesium oxide and hydrogen gas these are common questions that you could get so magnesium and cold water will give you magnesium hydroxide and magnesium and steam will give you magnesium oxide so mg plus H2 o produces mg plus H2 calcium reacts fairly vigorously with water to produce a white precipitate of calcium hydroxide and hydrogen gas so ca+ 2 H2O produces CA o taken twice plus H2 you need to be able to write these equations the next thing is the reaction with oxygen magnesium calcium and berium they tarnish in air what this means is that they readily form an oxide layer around them so in order to get magnesium to burn you will have to scrape the oxide layer off of the magnesium before it can be burnt in oxygen and the reaction is 2 mg plus O2 produces 2 MGO we get magnesium oxide in this case and this reaction occurs with a blinding White Flame calcium does not start burning easily again because of the oxide layer but when it does it bursts into flame to form carbon calcium oxide so 2 CA plus O2 produces 2 CAO reaction with hydrocloric acid now remember I said that the group two elements are alkaline earth metals so a metal plus an acid will give us a salt and hydrogen gas so magnesium will react with hydrochloric acid to produce magnesium chloride and hydrogen gas so mg+ 2 HCL produces mgcl2 plus H2 calcium we get a similar reaction calcium plus hydrochloric acid will give us calcium chloride and hydrogen gas so CA plus 2 HCL produces ca2 plus H2 gas now this table summarizes the reaction between magnesium and calcium magnesium is higher up in the group and calcium is lower down in the group so the reaction with water in the case of magnesium the reaction is very slow with cold water but is vigorous with steam to form magnesium oxide and hydrogen in the case of calcium the reaction is vigorous with cold water at first but slows down as the sparingly soluble hydroxide is formed and hydrogen gas is also produce the reaction would dilute hydrochloric acid so the acid in this case we are talking about is HCL in the case of magnesium you have a rapid reaction you get magnesium chloride being produced as well as hydrogen gas for calcium it's a very rapid reaction with dilute hydrochloric acid calcium chloride is produced and hydrogen gas is produced in the case of the reaction with oxygen in air the layer of oxide forms preventing further oxidation a brilliant flame is flame is produced as magnesium oxide is produced in the case of calcium the lay of oxide that forms around the calcium prevents further oxidation so what we saying as we go down group two reactivity increases and the reason for this is that the atomic radi increases down the group the attraction of the nucleus on the outer shell electrons decreases down the group and therefore the outer shell electrons are lost more readily and this is the reason why reactivity increases down the group let us now look at Trends in group seven in group s seven we have Florine chlorine bromine and iodine and we have the electronic configuration of each of them we'll notice that in the last shell the outermost shell we have seven electrons all right now in group seven the Florine chlorine bromine and iodine are called the halogens we also need to look at the physical properties of these elements Florine is a gas chlorine is a gas bromine is a dark red liquid and iodine is a dark gray solid so what you would notice is that as you go down the group the physical state changes from gas to liquid to solid now the group seven elements exist as diatomic molecules what this means is that the exists as in the case of chlorine it exists as cl2 in the case of bromine it exists as br2 and in the case of iodine it exists as I2 so you will you would not see a chlorine atom existing by itself it usually exists in combination with another chlorine atom in case of bromine this will also exists as a diatomic molecule and iodine will be the same as well now because they exist as diatomic molecules it means that between these molecules we will have some form of attraction between them now this force of attraction between the datomic molecules are very weak and they are called Vander walls forces now as you move down the group the strength of these forces increases and what this does is it forces the molecules to move closer together and it is because of this you move from a gas to a liquid then to a solid all right so this is why the physical state changes from gas to liquid to solid and it also explains why the melting point and boiling point increases down the group so let me just recap the group seven elements they exist as diatomic molecules because they exist as molecules we have weak inter molecular forces between them and these forces are called Vander walls forces as we move down the group the strength of the forces increases and brings the molecules closer together and that is why we have a change in physical state as you go down the group and that is why the melting point and boiling point increases down the group so what I'm saying is that you have a chlorine molecule you have next chlorine molecule you have a next chlorine mole molecule in choring gas now between the molecules you will have weak forces and these Dash lines represents the weak forces which are known as vandals forces and what I'm saying is that as you go down the group the strength of these forces increases now group seven elements are oxidizing agents right the oxidizing strength decreases as go on the group now in when something behaves as an oxidizing agent it is itself reduced when it behaves as an oxidizing agent right now oxidation is the loss of electrons so let's let's do let's say chlorine chlorine is able to form the chloride ion but an electron is lost in the process all right so if chlorine is AC acting as an oxidizing agent it is itself reduced so chlorine has an oxidation number of zero the chloride ion has an oxidation number of minus1 and we know that a decrease in oxidation number is called reduction all right so when chlorine acts as an oxidizing agent it is reduced so it goes from oxidation state 0o to minus1 now an element higher in the group displaces an element lower down in the group now this is a typical question that CXC likes to bring so for example if we take chlorine gas and bubble it through a solution of sodium bromide bromine will be displaced the observation is that a reddish brown liquid will form you also need to be familiar with this equation so cl2 plus 2 nabr produces 2 NAC plus br2 so just remember what the elements are you have chlorine chlorine bromine and iodine and what we are saying is that the one higher up in the group is able to displace the one lower down in the group so chlorine is here and chlorine is is able to sorry displace iodine chlorine can also displace bromine but bromine cannot displace chlorine it's always the one higher up in the group displacing The One lower down in the group now we need to look at period three and remember period the period uh the list of elements that go horizontally so in Period 3 we have sodium magnesium aluminium silicon phosphorus sulfur chlorine and Argon now if we look at electronic configuration we notice that the outer shell electron is different for each one but what you will notice is that you have one 2 three electron shells so just by looking at electronic configuration we can tell which period an element belongs to and earlier we said that the last number will tell you which group it belongs to now sodium magnesium and aluminium are metals and they have metallic characteristics silicon is semi metallic or sometimes referred to as a metaloid it shows both metallic and non-metallic characteristics phosphorus sulfur and chlorine are non-metals and show non-metallic characteristics so the general Trend As you move a across a period is from metallic to non-metallic character now you need to remember the first 20 elements of the periodic table and this is a trick that I usually tell my students you should learn them by groups because it is easier to remember the electronic configuration so in group one all you need to remember is lithium sodium potassium and we know we start off with 21 then it should be 281 and 2881 in group two we have bellium magnesium and calcium so we go 2 two 282 and 2882 in group three we have Boron and aluminium so we start off with 23 then 283 in group four we have carbon silicon which is 24 284 in group five we have nitrogen and phosphorus that is 2 five and 285 in group six we have oxygen and sulfur which is 26 and 286 and in group seven we have Florine chlorine which will be 27 and then 287 and in group8 or group some referred to as group zero we have helium neon and argon we just have two and then we have 28 and 288 now in group eight these are the noble gases and you need to know that they are very stable and the reason for this is that the outer shell electron is filled it has eight electrons in the outer shell now this partial periodic table here shows this is period three notice in electronic configuration we have three numbers this is period two notice we have two digits for each electronic configuration and like I said before the last number will tell you what group it belongs to so this belongs to group one this belongs to group two this belongs to group three now if you are given the El ronic configuration of an element you can determine the atomic number the group number and the period for example suppose you are given an electronic configuration of 281 just by looking at this number or this electronic configuration I can determine what group it belongs to the last number will tell me what what group it belongs to it's one so therefore I know this element belongs to group one we have three numbers one 2 three so therefore I know it belongs to period 3 I can also determine the atomic number the atomic number is simply 2 + 8 + 1 which is 11 so to get the atomic number from the electronic configuration we just need to add the digits that make up the electronic configuration and this element as we know is sodium now as I mentioned before the noble gases occupy group eight and are very stable and you will notice that they have eight electrons in their outer shell when elements react they attempt to achieve a stable structure by gaining or losing electrons or by sharing electrons right and in so doing they achieve a stable structure [Music]