Chemical Bonding

Definition of Chemical Bonding

Atoms are held together by the electrical attraction between positive and negative charges. When
atoms are held together they form all the compounds and materials that make up our world and the
universe.

How Atoms Combine
When an atom has a partly filled outer shell it is unstable and can react with other atoms. The atom
can lose, gain and even share its electron(s) with another atom.

Ionic Bonding
Ionic bonding is bonding between atoms when oppositely charged ions attract one another. An ion is
an atom which has lost or gained electrons and has become electrically charged positive or negative.

How Ions Form

Positive Ions

Lithium ion, +1 charge 

The lithium atom loses one electron. This means there are 3 protons and now 2 electrons. To explain how the charge on the lithium ion is worked out:

+3 (protons)
-2 (electrons)
+1 (overall charge)

Fluoride ion, -1 charge

The fluoride atom gains one electron. This means there are 9 protons and now 10 electrons. To explain how the charge on the fluoride ion is worked out:
+9 (protons)
-10 (electrons)
-1 (overall charge)

Forming an Ionic Bond

Fluoride ion F-

The lithium ion  combines with fluorine ion because they are oppositely charged and attract one another to form lithium fluoride.  Both atoms have full outer most energy levels.  A stable molecule.

Covalent Bonding

Covalent bonding is when electrons are shared between atoms. The sharing of these electrons binds the atoms together, as it fills the orbitals of both atoms and makes them stable.

Both atoms share the two electrons and fill the first orbital, This makes the new molecules stable.  The electrons can orbit both atoms.

Metallic Bonding
Metal atoms combine together in a lattice network. This means the metal atoms line up alongside one another. The outermost electrons are free to move through the lattice. When they all move in one direction they form an electric current.  

The following example of a copper (Cu) wire illustrates and describes how this occurs.

Electrons (black dots) flow from left to right

Electrons moving Copper wire are 
an electric current.

Another way to describe metallic bonding is metal atoms in a ‘sea of electrons’. Metals generally have high melting and boiling points due to a strong attraction in the metallic lattice.

Covalent Compounds
The compounds form when electrons are shared. The simplest example is Hydrogen gas, H2. Because
covalent compounds share electrons and form separate molecules they tend to have physical
properties which are:
• Low melting point
• Low boiling point.
Examples of covalent compounds are: CO2, NO2, NH3, H20

Ions with more than one atom
These are called polyatomic ions. They form a molecule held together by covalent bonding, but
because there is a surplus or deficit of electrons they are charged overall.

Examples are:

SO₄^2-  Sulfate
CO₃^2- Carbonate
NO₃^– Nitrate
OH^– Hydroxide
NH₄⁺ Ammonium
HCO₃^– Bicarbonate

The polyatomic ions can combine with an ion(s) of opposite charge to form a compound.

Examples are:

MgSO_{4    Magnesium Sulfate}

Ca(OH)_{2    Calcium Hydroxide}
The small number outside the brackets means there’s 2 molecules of hydroxide.