Robert Boyle, a chemist from Lismore County, Waterford is known as the father of chemistry. It was him who defined an element in 1661. Robert Boyle, a chemist from Lismore County, Waterford is known as the father of chemistry. It was him who defined an element in 1661. An element is a substance that cannot be spliced into simpler substances by chemical means.
200 years later, English chemist Humphry Davy discovered many elements by passing electricity through compounds. This was the first time in chemistry where chemists began to try and discover more and more of these elements. By the 1820s a number of elements had been discovered.
It was becoming more and more difficult to memorise all of these elements. It was four scientists who tried to define some pattern with elements which ultimately led to the creation of the modern periodic table. German chemist Johann de Bruyne noticed that properties of some elements were similar. For example, chlorine, bromine and iodine have similar reactive properties.
He noticed that the atomic weight of bromine was the average of chlorine and iodine. Back then the atomic weight was used instead of the atomic mass. However overall the scientific community disregarded his theory.
He is now credited because he was the first to see some sort of relationship between the properties and the atomic weight. You do not need to learn off the triad groupings. a group of three elements that have similar chemical properties in which the middle element is the average atomic weight of the other two.
This is the definition of a triad. 40 years later, English chemist John Newlands noticed that the properties of the elements seemed to repeat every eighth element. He called this Newlands octaves.
You do not need to turn off this table. Newlands Octaves are the arrangement of elements in which the first and eighth element have similar properties. However, Newlands did have some problems. He incorrectly assumed that all the elements at the time had been discovered and he tried to force these elements together.
This meant that the properties within groups did not align correctly. Also, at the time no noble gases had been discovered yet. However, despite these problems, his idea laid the foundations for Dimitri Mendeleev. Dmitry Mentaleev was a Russian chemist and it was him who ultimately created the periodic table. He wrote all the known elements on individual cards and arranged these cards in different orders.
He realised if he arranged the cards in accordance to increasing atomic weight, he got a pattern. He then put the elements into groups with similar properties. But most importantly, he left gaps for any undiscovered elements. Elements are arranged in order of increasing atomic weight.
The properties of these elements reoccur periodically. By leaving gaps, Mendeleev was essentially predicting the number of elements to be found. He was also predicting their properties due to them being in groups.
Many chemists were sceptical of Mendeleev and his proposed table, but they soon found out that his predictions were in fact correct. Mendeleev did have one problem besides the absence of some elements. He noticed for the properties to align correctly, he had to reverse one or two elements.
For instance, Tellurium with an atomic weight of 52 was placed after iodine with an atomic weight of 53 for their properties to align. Finally, it was English chemist Henry Moseley who 50 years later discovered why Mendeleev had to reverse some elements. Moseley, using x-rays, discovered how to find the quantity of protons in an atom.
He applied this to the atom. of the periodic table and he discovered that the periodic table should be arranged by the number of protons i.e. the atomic number and not the atomic weight. This meant that elements that meant the leave had previously reversed were in fact in the correct positions according to their atomic number.
Modern periodic law states elements are arranged in order of increasing atomic number and their properties of these elements reoccur periodically. Exams love asking for the differences between the modern periodic table and Mendeleev's periodic table. The atomic number is always a smaller number. It is defined as the number of protons in the nucleus of an atom.
The number of electrons is the same as the number of protons, providing that the atom is neutral and not an ion. An ion is an atom or group of atoms with a charge. For your leaving certificates you must be able to determine the number of subatomic particles in an ion. We will look at a positive ion, aluminium 3+.
A positive ion means it has lost electrons. Electrons are negative. Think about it.
If you took something negative away from your life, such as exams, you'd be a lot more positive. The same applies to electrons. Aluminium has lost three electrons because it is 3+. The atomic number, which is always...
is a smaller number is 13. Therefore for aluminium you have 13 protons and for neutral it would also have 13 electrons. However aluminium has lost 3 electrons so therefore it must only have 10 electrons left. The charge only relates to the number of electrons.
The number of protons and the number of neutrons never change. To calculate the number of neutrons, simply take the atomic number from the mass number, exactly as you would for a neutral atom. 13 from 27 is 14, so therefore there are 14 neutrons.
In this second example, you are given an unspecific ion, and asked to get the atomic number and the mass number. The atomic number is the number of protons in the nucleus of an atom. If the atom was neutral, It would have the same number of protons as it does electrons. This ion has lost two electrons, meaning it originally had 27 electrons.
Therefore it must have had 27 protons. The mass number is the number of neutrons and the number of protons added together. 27 plus 32 equals 59. Isotopes are defined as atoms of the same element, i.e. they have the same atomic number, but have different mass numbers due to a different number of neutrons.
Aspectrometer is an instrument used to discover isotopes. The instrument is used quite regularly in chemistry to discover the masses of an atom. You are asked to calculate the relative atomic mass of gallium.
You have two isotopes. Sometimes there are more than two isotopes. You do the exact same thing either way.
You multiply the percentage by the mass number. Then you add up the value of both isotopes which gives you the total mass of 100 atoms. We divide this by 100 to find the mass number of a single atom of gallium. The relative atomic mass is defined as the average mass numbers of the isotopes of the element, taking their abundances into account. It is based on 1 12th of the mass of the carbon 12 atom.
Because the relative atomic mass is an average of mass numbers, this means they are generally not whole numbers. For your LIMA certificate you need to be able to draw the mass spectrometer diagram and obviously label it. While it looks simple to draw you should practice the diagram.
In addition to this you need to be able to state the five processes occurring in the mass spectrometer. Step 1. Vaporisation. All samples need to be in a gaseous state, so solids and liquids may have to be heated here.
Step 2. Ionisation. The atoms must be charged, aka they must be an ion. An electron gun essentially bombards the atoms, causing positive ions to be produced, as electrons are knocked out of the sample.
Step 3 Acceleration The charged particles are fired through the chamber at high speed. Step 4 Separation in a magnetic field The electromagnet causes particles to be deflected. The lighter the particles the easier to deflect. In this case the blue line is the lightest particles whereas the red line is the lightest particles.
red line are the heaviest particles. Step 5 Detection. The detector notes where the ions hit the chamber.
From this it can detect the masses of these ions which then can be interpreted by chemists. Note the chamber is a vacuum so that no air molecules can interfere with the ions. The principle of mass spectrometry states that charged particles moving in a magnetic field are deflected to different extents according to their masses, and that they are separated due to these masses.
You should know at least three uses of the mass spectrometer. The electron configuration of atoms We previously came across this topic in the arrangement of electrons in an atom chapter. We will now look at these in more detail. The electron configuration shows the arrangement of electrons in an atom of an element.
There are four sub-levels, however for your leaving source you only need to know three. That is the sp and d sub-levels. The s sub-level can hold one orbital, therefore it has a max of two electrons.
The p sub-level contains contains 3 orbitals, therefore a max of 6 electrons, whereas the D sublevel contains 5 orbitals, meaning there's a max of 10 electrons. You do need to know this table. The upcoming examples will help you memorise it. The format of electron configurations is always the same which you can see here. How much you use of the electron configuration depends on the number of electrons in the atom you're using.
Just a quick point, you can see that the 4s sublevel is placed before the 3d sublevel. This is because the 4s sublevel contains less energy than the 3d sublevel. I find initially the electron configuration looks difficult but once you start practicing things become a lot easier. Let's look at fluorine.
It has nine protons. It's neutral therefore Fluorine has 9 electrons also. The superscript indicates the number of electrons. If we are using 9 electrons we will get as far as 2p5.
Phosphorus is also neutral therefore has 15 electrons. We get as far as 3p3 sublevel. Finally we are looking at magnesium ion.
Magnesium has 12 protons. If it were neutral it would have 12 electrons also. But it has lost 2 electrons as it is positive. Therefore the magnesium ion has 10 electrons.
we would get as far as the 2p6 sublevel. As always in chemistry there are a few exceptions to the rule. These exceptions will appear in trends in the periodic table chapter, so pay particular attention.
We will look at two examples. It was found for chromium that an electron from the 4s sublevel moves to the 2p6 sublevel. 3d sublevel to make 3d5.
They rearrange slightly because a half full or a completely full p or d sublevels are actually more stable. All atoms want to be as stable as possible. 3d5 is a half-filled sublevel.
For copper, an electron moves from the 4s sublevel to the 3d sublevel to completely fill that sublevel, making it more stable. Electrons always occupy the lowest available energy level in its ground state. Hund's rule states that electrons occupy their orbitals singularly before filling them in pairs.
This mainly applies to the p sub-level. Let's have a look at oxygen. Pauli exclusion principle states that no more than two electrons may occupy an orbital and they must have opposite spins.
We must be careful when answering these. If the question asks for orbitals, then you must write out the electron configuration the long way. That's with all the x, y and z orbitals included for the p sublevels.
Part asks for the number of sublevels. We count up the number of letters in total, just the letters. Remember, the 2 and 3p sublevels are only counted once each.
Part asks for the number of orbitals. Therefore, we count up everything. If we wanted to extend this question, The number of energy levels would equal to 3.