CHEMICAL BONDING
This is the joining/combination of two or more elements to form a new compound or molecule.
During bonding:
# Metals lose electrons and form positive ions (become positively charged).
#Non-metals gain electrons and form negative ions (become negatively charged).
An ION is an electrically charged particle or atom.
Positively charged ions (metal ions) are called CATIONS.
Negatively charged ions (nonmetal ions) are called ANIONS.
Formation of ions in metals
Examples
Draw the dots or cross diagrams to show how the following metals form ions.
- Sodium
- Boron
Exercise
Draw the dots or cross diagrams showing how the following metals form ions.
- Calcium
- Aluminium
- Magnesium
- Potassium
- Beryllium
- Lithium
Formation of ions in no-metals
Examples
Draw the dots or cross diagrams showing how the following non-metals form ions.
- Oxygen
Exercise
Draw the dots or cross diagrams showing how the following non-metals form ions.
- Chlorine
- Sulphur
- Fluorine
- Phosphorus
- Nitrogen
There are three types of bonding
# IONIC BONDING
# COVALENT BONDING
#METALLIC BONDING
- IONIC BONDING
Ionic bonding is the electrostatic force of attraction between oppositely charged ions.
It is the transfer of electrons from a metal to a non-metal.
NB: ionic bonding occurs between metals and non-metals.
Examples
Draw the dots and cross diagrams to show how the following ionic compounds are formed
- Sodium chloride
- Magnesium fluoride
Exercise
Draw the dots and cross diagrams to show how the following ionic compounds are formed
- Calcium chloride
- Sodium nitride
- Lithium oxide
- Magnesium phosphide
- Potassium sulphidek
- Aluminium oxide
COVALENT BONDING
This is the sharing of electrons between non-metallic elements.
NB: Covalent bonds are formed by non-metallic elements only
One pair of shared electrons (x
.) forms a single bond, which is represented by a dash (-).
Two pairs of shared electrons ( ) forms a double bond ( )
Three pairs of share electrons ( ) forms a triple bond ( ).
Examples
Draw the dots and cross diagrams to show how the following covalent compounds are formed
- Hydrogen chloride (HCl)
- Methane (CH4)
- Oxygen molecule (O2)
EXERCISE
Draw the dots and cross diagrams to show how the following covalent compounds are formed
- Hydrogen molecule (H2)
- Nitrogen (N2)
- Ammonia (NH3)
- Carbon dioxide (CO2)
- Water (H2O)
- Trichloro methane (CHCl3)
- Chlorine molecule (Cl2)
- Ethene (C2H4)
- Ethanol (C2H5OH)
METALLIC BONDING
A metallic bond is an electrostatic force of attraction between positive metal ions and in a sea of delocalized electrons. The electrons in the outer shell of the atom of the metal move freely throughout the structure (they are delocalized) forming a mobile sea of electrons.
The metal atoms consist of positive metal ions and free moving electrons the metal ions.
(Diagram)
- Metals are good electrical conductors’
This is due to the existence of freely moving electrons which can carry electric current around.
- Metals are malleable ie can be hammered into different shapes without breaking.
This is because the atoms of the same metal are the same in size, therefore they can easily slide over each other forming different shapes.
Properties of ionic and covalent compounds
Ionic compounds |
Covalent compounds |
| Usually liquids or gases at room temperature and pressure. Example; oxygen, water etc. Reason: The molecules are held by weak intermolecular forces |
| Have low and boiling points Reason: The atoms are held by weak forces which are easily broken down, so a small amount of energy is required to melt them |
| They do not conduct electricity
Reason: They do not have ions to carry current around |
| They are insoluble in water but soluble in organic solvents such as paraffin, benzene, acetone etc |
| They form simple molecular structures eg O2, H2O OR Giant molecular structures eg diamond and graphite |
|
They are volatile ie can easily turn into vapor |
LATTICE STRUCTURE OF SODIUM CHLORIDE
A lattice is a three dimensional arrangement of ions in a crystalline solid.
In the lattice structure of sodium chloride each sodium ion (Na+) is surrounded by six chloride ions (Cl–) and each chloride ion is surrounded by six sodium ions.
(diagram, quarter a page)
Giant molecular structures
- Diamond
Diamond consist of the element carbon. Each carbon atom is bonded to four other carbon atoms by single covalent bonds.
Diamond is the hardest natural substance because of the strong bonds and its rigid structure.
- Diamond does not conduct electricity because all the valence electrons of carbon atoms are used in bonding, therefore there are no free moving electrons to carry electric charge.
- Diamond also have a high melting point because it has strong covalent bonds, which need a lot (high amount) of energy to separate them.
- Graphite
In graphite each atom is bonded to three other carbon atoms in the same plane.
- Graphite has a high melting point because it strong covalent bonds.
- Graphite conducts electricity because it has some free moving electrons that carry electric current.
NB: Graphite is the only nonmetal that conducts electricity.
Inter-molecular and intra-molecular forces
An inter-molecular force of attraction is a weak force of attraction found between the molecules.
Inter- between
An intra-molecular force of attraction is a strong force of attraction found within the molecules
Intra- within