Bonding
Ionic
Covalent
(Metallic)
How do atoms bond(join) together to
form the millions of different
compounds that make up the world?
It all comes down to the electrons!
There are many ways electrons can interact with
one another:
• Electrons can be transferred between atoms
Ionic Bonding
• Electrons can be shared between atoms
Covalent Bonding
• Electrons can move freely between atoms
Metallic Bonding
Ionic Bonding
Ionic Bonding
• Metals react with non-metals
• Ions form when metalatoms donate electrons
to a non-metal atom
• Metals form +vecharged ions as they have
lostelectrons
• Non-metals form -vecharged ions as they have
gained electrons
• The positive and negative ions share a strong
electrostatic force of attraction – IONIC BOND
• Ions bond to form IONIC SUBSTANCES
Consider reactions between the following
metals and non-metals:
sodium + chlorine  sodium chloride
magnesium + oxygen  magnesium oxide
calcium + chlorine  calcium chloride
1 Sodium atom donates 1electron
1 Chlorine atom accepts 1 electron
This means…
For every 1 Sodium atom –
1 Chlorine atom is needed
Na1+
Cl1-
1 Magnesium atom donates 2electrons
1 Oxygen atom accepts 2 electrons
This means…
For every 1 Magnesium atom –
1 Oxygen atom is needed
Mg2+
O2-
1 Calcium atom donates 2electrons
1 Chlorine atom accepts 1 electron
This means…
For every 1 Calcium atom –
2 Chlorine atoms are needed
Cl1-
Ca2+
Cl1-
Have you noticed how electrons
are arranged within the shells?
Individually??
In pairs??
In groups??
Ionic Lattice
• Not just a pairof ions
• Many atoms (ions) bond to form an
IONIC LATTICE
• The number of positive and negative ions vary,
depending on how many electrons are
transferred between the metal and non-metal.
1 positive ion : 1 negative ion
Sodium loses 1 electron
Chlorine gains 1 electron
1 positive ion : 2 negative ions
Calcium loses 2 electrons
Chlorine gains 1 electron
Properties of Ionic Substances
The very strong ionic bonds within the lattice
means…
• HIGH melting point (usually over 250oC)
• HARD– when apply force the force is spread
throughout lattice
• BRITTLE– large force can cause ions to move,
therefore repel one another  lattice breaks
Properties of Ionic Substances
The very strong ionic bonds within the lattice
means…
• DO NOT conduct ELECTRICITY when solid –
ions are not free to move
• WILL conduct ELECTRICITY when in aqueous
solution– ions are now free to move
Examples of Ionic Substances
Sodium Chloride
Magnesium Oxide
Calcium Chloride
Can you think of some others?...
Covalent Bonding
Covalent Bonding
• Most compounds (substances) in the world
are formed through covalent bonding
• Non-metals react with non-metals
• Atoms shareapairofelectrons– this is called a
COVALENT BOND
• Two types of covalent bonds:
Covalent Molecular ANDCovalent Network
Covalent Molecular
• Electron clouds of atoms
overlapand interact to
share electrons
• Strong ‘electrostatic’
attraction between the
positive nucleus and
negative electrons –
keeps atoms together
• Form molecules
Cl
Cl
Chlorine has 7 electrons
in its valence shell.
It needs 1 electron for
this shell to be full.
How will 2
chlorine atoms
react and bond?
Cl Cl
Each atom of Chlorine achieves
a full valence shell by sharing
the 2 electrons in the middle.
How many bonds?
• Atoms may form multiple covalent bonds - share not just
one pair of electrons, but two or more pairs
• Atoms of different elements will form either one, two,
three or four covalent bonds with other atoms
• Number of covalent bonds is equal to eight minus the
group number:
Group
4
5
6
7
Example
Carbon
Nitrogen
Oxygen
Fluorine
# of Bonds
8–4=4 8–5=3
8–6=?
8–7=?
• Hydrogen forms one covalent bond, and the noble
gases in Group VIII do not form covalent bonds at all.
•Oxygen has 6 electrons in its valence shell, therefore needs
2 electrons for this shell to be full.
•2 Oxygen atoms share 2 electrons (2 bonds)–
this fills both of their valence shells.
•Nitrogen has 5 electrons in its valence shell, therefore
needs 3 electronsfor this shell to be full.
•2 Nitrogen atoms share 3 electrons (3 bonds)–
this fills both of their valence shells.
Arrangement
• Do not form a lattice
• Remain as individual molecules
• Interact weakly with other molecules
• Covalent molecules can be small and simple
• Covalent molecules can be largeand complex
Properties of Covalent Molecular
Substances
• GASES and LIQUIDS at room temperature – OR
easily melted solids
• LOWmelting points – forces between atoms are
strong, BUT forces between molecules are weak
• DO NOT conduct electricity – no charged
particles (ions)
Covalent Network
• Do not exist as individual molecules
• Form giant networks of covalently bonded
atoms
• Carbon (C) and Silicon (Si)
• Diamonds – carbon atoms form 3D network
• Silica (found in sand) – silicon and oxygen
atoms form a 3D network
Properties of Covalent Network
Substances
• HARD and BRITTLE
• HIGH melting points – strong covalent bonds
between molecules in network
** Diamonds melt at just over 4000oC!
• DO NOTconduct ELECTRICITY – no charged
particles (ions)
• INSOLUBLE in water – the bonds will not
break if you add substance to water
• Non-reactors
Examples of Covalent Substances
Carbon Dioxide
Methane
Diamonds
Can you think of some others?...