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BondingBonding

Hi. My name’s Johnny Chlorine. I’m in Group 7, so I have 7 electrons in my outer

shell

I’d quite like to have a full outer shell. To do this I need to GAIN an electron. Who can

help me?

Cl

Cl

21/04/23

BondingBondingHere comes one of my friends,

Harry Hydrogen

Hey Johnny. I’ve only got one electron but it’s really close to my nucleus so I don’t want to

lose it. Fancy sharing?

Cl

H

Cl

H

Now we’re both really stable. We’ve formed a covalent

bond.

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Covalent bondingCovalent bondingConsider an atom of hydrogen:

Notice that hydrogen has just __ electron in its outer shell. A full (inner) shell would have __ electrons, so two hydrogen atoms get together and “_____” their electrons:

Now they both have a ____ outer shell and are more _____. The formula for this molecule is H2.

H - H

Note that often a covalent bond is represented by a straight line

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Dot and cross diagramsDot and cross diagramsWater, H2O:

Oxygen, O2:

Step 1: Draw the atoms with their outer shell:

Step 2: Put the atoms together and check they all have a full outer shell:

OH H

O=O

H

HH

O

O O O O

O H

Your turnYour turn21/04/23

Draw dot and cross diagrams for N2, CH4, NH3 and CO2

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Dot and cross diagramsDot and cross diagramsNitrogen, N2:

Carbon dioxide, CO2:Ammonia NH3:

Methane CH4:

N=N

H

H - C – H

H

H-N-H

HO=C=O

Displayed formula

N N

O OC

C

H

H

H

H

NH H

H

EXAMPLES :

Draw dot-and-cross diagrams to represent the covalent bonding in each of the following molecules :

11 HydrogenHydrogen HH22

22 NitrogenNitrogen NN22

33 WaterWater HH22OO

44 Carbon dioxideCarbon dioxide COCO22

55 Hydrogen peroxideHydrogen peroxide HH22OO22

66 TetrachloromethaneTetrachloromethane CClCCl4477 EthaneEthane CC22HH66

88 EtheneEthene CC22HH44

Expanding the octetExpanding the octet21/04/23

Some elements can ‘expand their octet’. This means that they can, through covalent bonding, except more than 8 electrons into their outer shell. The explanation is that they use their empty d subshells to accommodate the new electronshis means that they can, through covalent bonding, except more than 8 electronsThe elements that do this that you need to be aware of areGp V – P, AsGp VI – S, Se, TeGp VII – Cl, Br, I, At

Reducing the octetReducing the octet21/04/23

In the same way some element (usually B, Be and Al) can have ‘reduced’ octets. That is they can, through covalent bonding, have less than 8 electrons in their outer. They gain the required stability through other means.

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H H

H

N

C OO

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Dative bond

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Metallic bondingMetallic bonding21/04/23

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