Atomic Structure - (Section 1c)

Atomic Structure 

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

The centre of an atom is known as the 'nucleus.' It consists of protons and neutrons, and has a positive charge because of the protons. Nearly the whole mass of the atom is concentrated in the nucleus, however it is tiny in size compared to the rest of the atom. The nucleus is surrounded by orbiting shells, or energy levels,  in which electrons lie. They are negatively charged, have virtually no mass and despite the fact they cover a lot of space, they are tiny.

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

Proton = Relative mass of 1, relative charge of +1.

Neutron, Relative mass of 1, relative charge of 0.

Electron, Relative mass of 0, relative charge of -1. 

1.11 understand the terms atomic number, mass number, isotopes and relative atomic mass

Atomic number = the number of protons (and therefore electrons as these two vales are the same) within an atom. 

Mass number = the total number of protons and neutrons within an atom.

Isotopes = Different atomic forms of the same element, which have the same number of protons but a different number of neutrons. 

Relative atomic mass = the average mass of all the isotopes of an element. This is calculated from the masses and relative abundances of all the isotopes of a certain element. It is often given by the symbol Ar. 

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

In order to find the relative atomic mass of an element from the relative abundances of its isotopes, 
1) Multiply the mass of each isotope by its relative abundance 
2) Add these together.
3) Divide by the sum of the relative abundances. 

For example., work out the relative atomic mass of chlorine. 

Relative mass of isotopes = 35, 47.
Respective to above, relative abundances = 3,1.

1) Multiply the mass of each isotope by its relative abundance - (35x3), (37x1)
2) Add these together - 105 + 37 = 142
3) Divide by sum of relative abundances =  142/(3+1) = 142/4 
                                                                  = 35.5

So, the relative atomic mass of chlorine = 35.5

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

The elements of the Periodic Table are shown in order of increasing atomic number. Going horizontally and to the right, each element has an atomic number than the previous element. This can be seen in the periodic table, with the numbers above the symbols displaying each elements atomic number. 

1.14 deduce the electronic configurations of the first 20 elements from their positions in the periodic table. 

The number of electrons in an element is shown by the atomic number of the element. So, if an element has an atomic number of 16 (sulphur), then it has 16 electrons. To work out the electronic configuration, you count up to 16, keeping in mind the number of electrons allowed per each shell in an element. As there are 2 electrons allowed in the first shell, and eight in the following two shells, sulphur will have an electronic configuration of 2.8.6

You can check this is correct using the elements' position in the periodic table. The vertical columns in the periodic table are known as groups. The number group an element is in tells you how many electrons that element has in its outer shell. Sulphur is in group 6 of the periodic table, and will therefore have six electrons in it's outer shell. The horizontal columns in the periodic table are known as periods. The number period an element is in tells you how many energy levels the element has. Sulphur is in period three of the periodic table, and will therefore have three energy levels, so the electronic configuration above is correct. 

1.15  deduce the number of outer electrons in a main group element from its position in the Periodic Table. 
The number of the group (vertical column) an element is in corresponds to the number of electrons there are in it's outer shell.For example, Boron is in group 3 of the Periodic Table and therefore has 3 electrons in its outer shells.