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.

  1. Sodium
  2. Boron

 

 

Exercise

Draw the dots or cross diagrams showing how the following metals form ions.

  1. Calcium
  2. Aluminium
  3. Magnesium
  4. Potassium
  5. Beryllium
  6. Lithium

 

 

Formation of ions in no-metals

Examples

Draw the dots or cross diagrams showing how the following non-metals form ions.

  1. Oxygen

Exercise

Draw the dots or cross diagrams showing how the following non-metals form ions.

  1. Chlorine
  2. Sulphur
  3. Fluorine
  4. Phosphorus
  5. Nitrogen

There are three types of bonding

# IONIC BONDING

# COVALENT BONDING

#METALLIC BONDING

  1. 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

  1. Sodium chloride
  2. Magnesium fluoride

Exercise

Draw the dots and cross diagrams to show how the following ionic compounds are formed

  1. Calcium chloride
  2. Sodium nitride
  3. Lithium oxide
  4. Magnesium phosphide
  5. Potassium sulphidek
  6. 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

  1. Hydrogen chloride (HCl)
  2. Methane (CH4)
  3. Oxygen molecule (O2)

     

     

EXERCISE

Draw the dots and cross diagrams to show how the following covalent compounds are formed

  1. Hydrogen molecule (H2)
  2. Nitrogen (N2)
  3. Ammonia (NH3)
  4. Carbon dioxide (CO2)
  5. Water (H2O)
  6. Trichloro methane (CHCl3)
  7. Chlorine molecule (Cl2)
  8. Ethene (C2H4)
  9. 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

  1. They are usually hard crystalline solids at room temperature and pressure.

    Reason:

    They have strong electrostatic force of attraction between the ions that hold them together

Usually liquids or gases at room temperature and pressure. Example; oxygen, water etc.

Reason:

The molecules are held by weak intermolecular forces

  1. They have high melting and boiling points

    Reason:

    Their ions are held by strong forces of attraction, as a result a lot of energy is needed to separate or break the ions.

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

  1. They conduct electricity when molten or in solution.

    Reason:

    In solid state, the ions are strongly attracted to each other hence they cannot carry current around, but when molten or in solution there is free movement of ions which can carry current around

They do not conduct electricity

 

Reason:

They do not have ions to carry current around

  1. They are soluble in water ie they dissolve in water but insoluble in organic solvents like ethanol, paraffin etc.

They are insoluble in water but soluble in organic solvents such as paraffin, benzene, acetone etc

  1. They form regular three dimensional structures called a LATTICE eg sodium chloride lattice

They form simple molecular structures eg O2, H2O

OR

Giant molecular structures eg diamond and graphite

 

  1. They are non-volatile (cannot easily turn into vapor)


 

 

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

  1. 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.
  1. 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


 

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