1. The Periodic Table, Valence Electrons and Bonding
How Elements Form Compounds

2. I CAN describe chemical bonding and determine an ionic chemical formula.

3. Chemical Bonding
Chemical Bonding is the joining of two or more atoms to form a compound.
Bonding occurs when atoms transfer electrons between them, or, in some cases, move close together and share electrons between them.

4. Valence Electrons
During bonding, the only electrons involved are those at the outer edge of the atom’s electron cloud.
These are called VALENCE ELECTRONS.
Atoms can have between 1 and 8 Valence Electrons [Ve-].

5. When atoms come into close contact with each other, VALENCE ELECTRONS can be TRANSFERRED from one atom to another.
Typically, atoms on the LEFT SIDE of the periodic table [the METALS] LOSE electrons.
Atoms on the RIGHT SIDE of the periodic table [the NON-METALS] gain electrons.

6. The number of electrons GAINED or LOST depends on the GROUP NUMBER the atom is in:
LOSE ELECTRONS GAIN ELECTRONS
Group 1 loses 1e- Group 15 gains 3 e-
Group 2 loses 2 e- Group 16 gains 2 e-
Groups 13 loses 3 e- Groups 17 gains 1 e-

7. Atoms become IONS
When an atom gains or loses electrons and there is a change in its overall charge, the atom is transformed into another form called an
ION

8. POSITIVE IONS are called CATIONS and are formed from METALS.
NEGATIVE IONS are called ANIONS and are formed from NON-METALS.

9. Charges of IONS Family 1 ions = +1 Family 2 ions = +2
[Family 14 bonds in a different way – more later]
Family 15 ions = -3
Family 16 ions = -2
Family 17 ions = -1
[Family 18 doesn’t form chemical bonds.]
Losing electrons is called OXIDATION and make + charged ions.
Gaining electrons is called REDUCTION and make - charged ions.

10. IONIC BONDING
IONIC BONDING occurs between two IONS with OPPOSITE CHARGES.
Remember OPPOSITES ATTRACT!

11. Characteristics of IONIC Compounds
Generally consist of a METAL CATION and a NON-METAL ANION.
High melting points
Almost always solid at room temperature
Brittle
Generally not very flammable
Dissolve in water [electrolytes]

12. Forming an IONIC Compound
What would be the formula for a compound resulting from ionic bonding between Potassium and Bromine?
STEPS
1. Find the elements in the Periodic Table and write down their symbols.
2. Use the element’s location on the Periodic Table to predict the charge of its ION.
3. Criss-cross the charges (NO SIGNS) and multiply.
4. Write the FORMULA.

13. Write the symbols and charges in a BRACKET above the symbols in this manner:
[ +1 ] [ -1 ] = 0
K Br

14. BALANCE the charge by criss-crossing the numbers [don’t worry about charge] and multiplying each bracket.
1 [ +1 ] [ -1 ] = 0
K Br

15. 1[ +1 ] + 1[ -1 ] = 0 K Br K1 Br1 To write the FORMULA,
Write the symbol of the POSITIVE ION first, the NEGATIVE ION second.
Place the number you MULTIPLIED the bracket by AFTER and slightly BELOW the symbol.
This number is called a SUBSCRIPT.
1[ +1 ] + 1[ -1 ] = 0
K Br
K Br1

16. So the formula for a compound of Potassium and Bromine is:
If the number is ONE, it is understood and you DO NOT have to write it.
Think of X in math….1X = X
So the formula for a compound of Potassium and Bromine is:
KBr

17. PROBLEM
What is the formula for an ionic compound of Magnesium and Chlorine?

18. Mg Cl Mg1Cl2 = MgCl2 1 [+2 ] + 2 [-1 ] = 0
Determine the symbol and charge of both elements and cross the numbers:
1 [+2 ] + 2 [-1 ] = 0
Mg Cl
Mg1Cl2 = MgCl2
Remember ONE is not usually written as a subscript!

19. Problem
What is the formula of an ionic compound of Aluminum and Oxygen?
[ +3] + [ -2 ]
Al O

20. [ +3] [ -2 ]
Al O

21.
2 [ +3] [ -2 ] = 0
Al O

22. So the formula becomes:
Al2O3