Formation of compounds

What happens when a piece of burning sodium is placed in a gas jar of chlorine?
+ sodium chlorine sodium chloride

Before Bonding
Na
Cl sodium = 11 electrons :
2, 8, 1 chlorine = 17 electrons :
2, 8, 7
Sodium gives 1 electron to chlorine

Na
Cl sodium ion
Charge
11 protons
10 electrons
+ 1
Na + = 2 , 8 chloride ion
Charge
17 protons
18 electrons
- 1
Cl = 2, 8, 8

After Bonding
Na Cl
This type of bonding is known as ionic bonding because the metal atoms transfer electron(s) to non-metal atoms and ions are formed.
Sodium atom loses an electron to form sodium ion Na +
Chlorine atom gains an electron to form chloride ion
Cl -
Chemical formula of sodium chloride is NaCl

When metal meet non-metals, the sparks will fly
“Give me the electrons!” non-metal do cry
“you got a deal!” the metal responds
The ions attract to form their bonds.

Lithium + fluorine
 lithium fluoride
Before Bonding
Li
F lithium = 3 electrons :
2, 1 fluorine = 9 electrons :
2, 7
Lithium gives 1 electron to fluorine

Li
F lithium ion
Charge
3 protons
2 electrons
+ 1
Li + = 2 fluoride ion
Charge
9 protons
10 electrons
- 1
F = 2, 8

After Bonding
Li
F
Lithium atom loses an electron to form lithium ion Li +
Fluorine atom gains an electron to form fluoride ion F
-
Chemical formula of lithium fluoride is LiF

What happens when a piece of magnesium is burnt in air?
magnesium + oxygen  magnesium oxide

Before Bonding
Mg
O magnesium = 12 electrons :
2, 8, 2 oxygen = 8 electrons :
2, 6
Magnesium gives 2 electrons to oxygen

2 +
2 -
Mg
O magnesium ion
12 protons
Charge
10 electrons
+ 2
Mg 2+ = 2 , 8 oxide ion
Charge
8 protons
10 electrons
- 2
O 2= 2, 8

After Bonding
2 +
Mg
2 -
O
Magnesium atoms lose 2 electrons to form magnesium ions Mg 2+
Oxygen atoms gain 2 electrons to form oxide ions O 2-
Chemical formula of magnesium oxide is MgO

Mg
Mg = 12 electrons:
2, 8, 2
Cl = 17 electrons : 2, 8, 7
Cl
Cl

Mg
Mg 2+
= 2 , 8
Cl -
= 2 , 8, 8
2 +
Cl
Cl

After Bonding
Mg
2 +
2 Cl
Magnesium lost 2 electrons to form magnesium ions Mg 2+
Each chlorine atom gained an electron to form chloride ions Cl –
Magnesium chloride is MgCl
2

Sodium oxide
Na
Na: 11 electrons :
2, 8, 1
Na
O
O : 8 electrons :
2, 6

Na
Na + = 2 , 8
O 2= 2, 8
Na
O
2-

After Bonding
2
Na
O
Each sodium atom lost an electron to form sodium ions Na +
An oxygen atom gained 2 electrons to form an oxide ion O 2-
Sodium oxide is Na
2
O
2-

K
Potassium sulphide
S
S : 16 electrons :
2, 8, 6
K: 19 electrons :
2, 8, 8, 1
K

S
2-
K
K + : 2, 8, 8
K
S 2: 2, 8, 8

After Bonding
2 K
S
Each potassium atom lost an electron to form potassium ions K +
A sulphur atom gained 2 electrons to form sulphide ion S 2-
Potassium sulphide is K
2
S
2-

Al = 13 electrons:
2, 8, 3
Al
F
F
F
F = 9 electrons : 2, 7

Al 3+ : 2, 8
Al
3 +
F
F
F
F : 2, 8

After Bonding
Al
3 +
3
F
Aluminium atom lost 3 electrons to form aluminium ions Al 3+
Each fluorine atom gained an electrons to form fluoride ion F
–
Aluminium Fluoride is AlF
3

Summary
Li
Na Mg
K Ca
Al
O F
S Cl
Metals transfer electrons to non-metal forming ions

Predict the formulas for the following ionic compounds:
Potassium bromide KBr
Lithium oxide Li
2
O
Magnesium sulphide MgS
Sodium iodide Na I
Aluminium chloride
AlCl
3
Calcium fluoride CaF
2