-state the relative charges and approximate relative masses of protons, neutrons and electrons

-Define proton number / atomic number as the number of protons in the nucleus of an atom

- Define mass number / nucleon number as the total number of protons and neutrons in the nucleus of an atom 

-Determine the electronic configuration of elements and their atoms with proton number 1 to 20

Example: sulfur atom.     Proton number is 16.

Mass number is 32. Since mass number = protons + neutrons, number of neutrons = mass number – proton number.

In this case is 32-16 = 16.  For an atom, number of protons is equal to number of electrons, so the number of electrons for sulfur atom is 16.

 

How to draw electronic structure of atom:

Note: first electron shell holds maximum 2 electrons.

Second electron shell hold maximum 8 electrons.

Third electron shell hold maximum 8 electrons (Not true for A levels, IB syllabus).

You can follow the numbers in sequence below to draw your electrons as a reference

 

Electronic configuration shows distribution of electrons of an atom in electron shells without drawing. First number stands for number of electrons in first shell, and second number, third and fourth number shows for number of electrons in second, third and fourth shell respectively. The numbers are separated by ‘dot’.

Electronic configuration of sulfur atom will be 2.8.6

The last number of the electronic configuration will show the valence/outermost electrons of the atom. Sulfur has 6 valence electrons. Sulfur atom also has 3 electron shells. 

Elements in the periodic table are arranged in increasing proton number.

State that:
- Group VIII noble gases have a full outer electron shell.

- the number of outer shell electrons is equal to the group number in Groups I to VII. [Do check the Periodic Table diagram in your syllabus to write either 1 to 18 or Roman numerals (I–VIII) ]
-the number of occupied electron shells is equal to the period number

Noble gases (Group VIII or 18) have fully filled electron shells and stable electronic configuration so they do not need to gain or lose electrons. Noble gases are inert and unreactive.

Atoms of Elements in same group (vertical column) have same number of valence electrons and similar chemical properties. 

Eg: Lithium and sodium are in group 1 as they their atoms have 1 valence electron.  They have similiar chemical properties as both elements can react with water. 

Atoms of elements in the same period (horizontal row) have same number of electron shells.

Eg: Sodium and magnesum are in Period 3 as their atoms have 3 electron shells.