Everything in the universe is made up of atoms. These incredibly small particles have unique combinations of three even smaller sub-atomic particles called protons, neutrons and electrons In atoms the number of protons and electrons are the same. However, the number of neutrons in atoms can vary. Different versions of atoms are called isotopes. They are different because they can have different numbers of neutrons crammed into the nucleus. Isotopes always have the same numbers of electrons and protons and therefore react in the same way. Over 100 different types of atoms (elements) are placed in the Periodic Table. The elements are arranged in ascending order by their proton number. The proton number is also called the atomic number. The mass number for a particular element is found when you add together the two sub-atomic particles, which have mass, i.e. the protons and neutrons.

The periodic Table is broken up into four different blocks given the letters s, d, p and f blocks. These four areas have been shown in different colours.

s-block = groups 1 and 2

p-block = groups 3 through to 0 (8)

d-block = Transition metals between groups 2 & 3

f-block are only studied in detail beyond A-level.

It is important to remember that the chemistry for a particular group or element results from the arrangement of the outer electrons. By gaining, losing or sharing outer electrons elements react in an attempt to achieve the more stable full outer electron structure typical of the noble gases.

At AS level chemistry electrons are placed in shells (1, 2, 3, 4 etc( and sub-shells (s, p, d, f). The electrons are put into a particular order for an element following the Aufbau Principle. Electron shells are spaces where there is a greater than 99 % probability that electrons will be found. The following table is useful when checking the answer to an elements electronic structure.

Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8

s1 s2 s2p1 s2p2 s2p3 s2p4 s2p5 s2p6

Transition metals will be dealt with separately as they are much more interesting. Once an AS student can quickly work out electron arrangements it is then time to study the chemical reactions. This is the bit of chemistry that everyone seems to enjoy. Don’t forget that the chemistry depends on the outer (valence) electrons.

Now it is time to meet the chemists toolkit the MOLE. Without lots of practice you will soon be left behind when it comes to examination questions. The mole has many definitions and is also referred to as Avogadro’s constant. Several mole equations and types of calculation recur throughout a chemistry course. Once these are mastered the chemistry course gets a lot easier. But you’ll need to keep practicing… You need to be able to rearrange equations with one unknown variable. The triangle method is quite useful for this simple maths. Maths is an important part of chemistry and you’ll soon learn to calculate both empirical and molecular formulae. This old fashion type of calculation will help you to understand modern techniques like mass spectroscopy. This is a way of telling you what a compound is, how big it is and what elements, and isotopes are present.

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