Section 1 c) Specification

1.9 understand that atoms consist of a central nucleus, composed of protons
and neutrons, surrounded by electrons, orbiting in shells

An atom is composed of a nucleus, made up of positively charged protons and neutrons, which have no charge. Each of these sub-atomic particles has a relative atomic weight of 1.

The nucleus is surrounded by shells of negatively-charged electrons, which have a relative atomic weight of 1. The shells of an atom are described at GCSE level as the first shell containing 2 electrons, and further shells having a capacity of 8 electrons.

1.10 recall the relative mass and relative charge of a proton, neutron and electron

Proton: Relative mass 1, Relative charge +
Neutron: Relative mass 1, Relative charge 0
Electron: Relative mass 0, Relative charge -

1.11 understand the terms atomic number, mass number, isotopes and relative
atomic mass (Ar)

Atomic Number: The number of protons in an atom
Mass Number: The number of protons + the number of neutrons in an atom
Isotopes: Atoms with the same number of protons and electrons, but a different number of neutrons.
Relative Atomic Mass: The mass of an atom relative to Carbon 12.

1.12 calculate the relative atomic mass of an element from the relative
abundances of its isotopes

(Mass 1 x Abundance 1) + (Mass 2 x Abundance 2) + .....
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                                           100       

1.13 understand that the Periodic Table is an arrangement of elements in order of
atomic number

The Periodic Table was developed by Mendelev as a way of organising the chemical elements by reactivity and characteristics. The patterns relate to the number of protons and electrons in each atom, and as a result the properties of undiscovered elements can be predicted fairly precisely. It is organised in chronological order of atomic number.
Each period relates to the number of shells of electrons, and each group relates to the number of outer shell electrons.

1.14 deduce the electronic configurations of the first 20 elements from their
positions in the Periodic Table

The first two elements are hydrogen and helium, which have 1 outer shell, with electronic configurations 1 and 2 respectively.
The second period contains 8 elements, with (left to right) electronic configurations
2,1 , 2,2 , 2,3 , 2,4 , 2,5 , 2,6 , 2,7 , 2,8
The third period resembles the second:
2,8,1 , 2,8,2 , 2,8,3 , 2,8,4 , 2,8,5 , 2,8,6 , 2,8,7 , 2,8,8
and so on.

1.15 deduce the number of outer electrons in a main group element from its
position in the Periodic Table.

The 8 groups of the periodic table tell us how many outer shell electrons the elements of the group have.
Group 1 : 1 valence electron
Group 2 : 2 valence electrons
etc.
etc.
Group 0 : full outer shell, so 2 or 8 valence electrons.