1. CHEMICAL BONDING

2. INTRODUCTION Cl Atoms do not tend to exist on their own
Most often, they are found joined together, by CHEMICAL BONDS
This is true of elements and compounds: H O Cl
The only exceptions are the Noble Gas elements

3. TYPES OF BONDING There are 3 types of chemical bond:
Covalent – found in elements and compounds
Ionic – found only in compounds
Metallic – found only in elements

4. BONDING IN ELEMENTS He Only the Noble Gases exist as single atoms,
e.g. Helium

5. A molecule is a group of atoms covalently bonded together
BONDING IN ELEMENTS 2
All other elements in the Periodic Table have bonds between their atoms
In all non-metals, these are COVALENT bonds
All these non-metal elements are therefore made up of MOLECULES
A molecule is a group of atoms covalently bonded together

6. MOLECULES O P P P P Cl Cl H O

7. BONDING IN COMPOUNDS Covalent bonding also occurs in compounds
The elements involved must both be NON-METALS
Examples:
Hydrogen oxide, carbon dioxide, nitrogen hydride
So non-metal compounds are made up of molecules

8. COVALENT BONDS + - + - - +
The positive nucleus of one atom attracts the negative electrons of another atom
At the same time, the two positive nuclei repel each other
The electrons are therefore held between the two atoms in a balance between these attracting and repelling forces
The electrons are SHARED between the two atoms

9. ENERGY LEVELS
Electrons are arranged around the nucleus in ENERGY LEVELS
The first energy level can hold TWO electrons
Once the atom has more than two electrons, the first energy level is full
Electrons are then found in the second energy level, which can hold EIGHT electrons
Hydrogen
Lithium
Oxygen
Helium
Boron
Neon

10. ENERGY LEVELS 2
Once the second energy level is full, the third one starts to fill.
The third energy level can hold EIGHT electrons
NOTICE:
Each time a new PERIOD is started, a new ENERGY LEVEL starts to fill
As you move across a period from left to right, a new electron is added to the same energy level
The number of electrons an atom needs to fill its OUTER energy level is the same number as its VALENCY
Sodium
Magnesium
Chlorine
Argon

11. COVALENT BONDS 2 Atoms form bonds in order to become more stable
This stability is associated with having 8 electrons in their outer energy level (like the noble gases)
In covalent bonding, atoms SHARE OUTER ELECTRONS so that all atoms involved have FULL OUTER ENERGY LEVELS

12. COVALENT BONDS 3 Here, each fluorine atom SHARES ONE electron
Both atoms now have EIGHT OUTER ELECTRONS
Both their outer energy levels are FULL
Note that the number of electrons an atom shares is equal to its VALENCY

13. IONIC BONDING Formed in compounds made up of a METAL and a NON-METAL
Examples:
Lithium chloride, Magnesium sulphide
Does not involve sharing electrons like covalent bonding
Instead, there is TRANSFER of electrons

14. IONIC BONDING 2 Sodium Fluorine
The atom LOSES ONE electron to leave a FULL ENERGY LEVEL. This is easier than gaining seven electrons.
The atom GAINS ONE electron to leave a FULL ENERGY LEVEL.

15. IONIC BONDING 3
The number of electrons that an atom LOSES OR GAINS is equal to the VALENCY
Metals always LOSE electrons
Non-metals always GAIN electrons
Both atoms then have FULL OUTER ENERGY LEVELS, and are stable

16. IONS
As an atom, lithium has 3 POSITIVE protons and 3 NEGATIVE electrons
When forming an ionic bond, the lithium atom LOSES one electron
The atom now has 3 POSITIVE protons and 2 NEGATIVE electrons
The overall charge is now 1 POSITIVE (1+)
An atom which has a charge like this, either positive or negative, is called an ION.
Ionic compounds are therefore NOT made up of atoms or molecules, but are made up of IONS.

17. IONS 2
The fluorine atom has 7 POSITIVE protons and 7 NEGATIVE electrons
When forming an ionic bond, the lithium atom GAINS one electron
The fluorine atom now has 7 POSITIVE protons and 8 NEGATIVE electrons
The overall charge is now NEGATIVE 1 (1-)
Fluorine
Note that when bonds form, it is the number of electrons which changes but the number of protons ALWAYS stays the same.

18. SUMMARY COVALENT BONDING IONIC BONDING
In both types of bonding, atoms are joining together in order to achieve a stable electron arrangement
This means that the OUTER ENERGY LEVEL must be FULL (like the Noble Gases)
COVALENT BONDING
IONIC BONDING
When found
Elements (except Noble Gases)
Compounds of non-metals only
Compounds of metals with non-metals
Compound made up of…
Molecules
Ions
Electrons are…
Shared
Transferred
Relationship to valency number
Number of electrons shared
Number of electrons transferred