BondingIonic

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 atomsIonic Bonding

• Electrons can be shared between atomsCovalent Bonding

• Electrons can move freely between atomsMetallic Bonding

Ionic BondingIonic Bonding

Ionic BondingIonic 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 1electron1 Chlorine atom accepts 1 electron

This means…For every 1 Sodium atom – 1 Chlorine atom is needed

Na1+ Cl1-

1 Magnesium atom donates 2electrons1 Oxygen atom accepts 2 electrons

This means…For every 1 Magnesium atom – 1 Oxygen atom is needed

Mg2+ O2-

1 Calcium atom donates 2electrons1 Chlorine atom accepts 1 electron

This means…For every 1 Calcium atom – 2 Chlorine atoms are needed

Ca2+

Cl1-

Cl1-

Have you noticed how electrons are arranged within the shells?

Individually??In pairs??

In groups??

Ionic LatticeIonic 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 ionSodium loses 1 electronChlorine gains 1 electron

1 positive ion : 2 negative ionsCalcium loses 2 electronsChlorine gains 1 electron

Properties of Ionic SubstancesProperties 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 SubstancesProperties 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 SubstancesExamples of Ionic Substances

Sodium ChlorideMagnesium OxideCalcium Chloride

Can you think of some others?...

Covalent BondingCovalent Bonding

Covalent BondingCovalent 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 MolecularCovalent 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

Chlorine has 7 electrons in its valence shell.

It needs 1 electron for this shell to be full.

How will 2chlorine atomsreact and bond?

ClCl

Cl ClEach atom of Chlorine achieves a full valence shell by sharing the 2 electrons in the middle.

How many bonds?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:

• Hydrogen forms one covalent bond, and the noble gases in Group VIII do not form covalent bonds at all.

Group 4 5 6 7

Example Carbon Nitrogen Oxygen Fluorine# of Bonds 8 – 4 = 4 8 – 5 = 3 8 – 6 = ? 8 – 7 = ?

•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.

ArrangementArrangement

• 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

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 NetworkCovalent 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

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 SubstancesExamples of Covalent Substances

Carbon DioxideMethaneDiamonds

Can you think of some others?...