Page 15 - Big Ideas Year 10 sciPAD 2025
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SCIPAD - BIG IDEAS - BOOK 2
NATURE OF THE ATOM
So sodium goes from an electron configuration of 2,8,1 with no charge, to an ion with an electron
configuration of 2,8 and a charge of +1.
1. Define the term ‘ion’. 
2. Why do atoms gain or lose electrons? 

3. Magnesium has an atomic number of 12. So it has 12 electrons arranged as 2,8,2.
(a) How many electrons are there in magnesium’s outer shell? 
(b) How many electrons does it need to gain to have a full outer shell? 
(c) How many electrons does it need to lose to have a full outer shell? 
(d) Is it going to be easier for a magnesium atom to gain or lose electrons? 
(e) What will be the final charge of the magnesium ion? 
4. Chlorine has an atomic number of 17. So it has 17 electrons arranged as 2,8,7.
(a) How many electrons are there in chlorine’s outer shell? 
(b) How many electrons does it need to gain to have a full outer shell? 
(c) How many electrons does it need to lose to have a full outer shell? 
(d) Is it going to be easier for a chlorine atom to gain or lose electrons? 
(e) What will be the final charge of the chloride ion? 
5. Neon has an atomic number of 10. So it has 10 electrons arranged as 2,8. Suggest why
neon is very unreactive. 

The Role of the Electron
During a chemical reaction, an atom wants to get a full outer shell of electrons. It can do this by
losing or gaining electrons, forming an ion.
A sodium atom has 1 electron in its outer shell. It can gain 7 electrons to get
a full outer shell of 8, or it can lose 1 electron and have a full second shell. It is
easier for the atom to lose one electron than gain 7.
During a reaction the sodium atom loses its outer shell electron and forms an
ion. An ion is an atom with an electrical charge.
After the reaction an ion with an
electrical charge has formed because:
11 Protons 		 = +11
12 Neutrons = 0
10 Electrons = -10
Total charge
=
+1
Prior to a chemical reaction the atom
has no electrical charge because:
11 Protons 		 = +11
12 Neutrons = 0
11 Electrons = -11
Total charge
=
0
An Example Using Sodium
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