25/10/2015Bonding 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

25/10/2015Bonding Here 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 H Now we’re both really stable. We’ve formed a covalent bond.

25/10/2015 Covalent bonding Consider 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 H 2. H - H Note that often a covalent bond is represented by a straight line

25/10/2015 Dot and cross diagrams Water, H 2 O: Oxygen, O 2 : Step 1: Draw the atoms with their outer shell: Step 2: Put the atoms together and check they all have a full outer shell: O H O=O H H H O OOOO O H

Your turn 25/10/2015 Draw dot and cross diagrams for N 2, CH 4, NH 3 and CO 2

25/10/2015 Dot and cross diagrams Nitrogen, N 2 : Carbon dioxide, CO 2 : Ammonia NH 3 : Methane CH 4 : N=N H H - C – H H H-N-H H O=C=O Displayed formula NN O O C C H H H H N H H H

EXAMPLES : Draw dot-and-cross diagrams to represent the covalent bonding in each of the following molecules :1Hydrogen H2H2H2H22Nitrogen N2N2N2N2 3Water H2OH2OH2OH2O 4 Carbon dioxide CO 2 5 Hydrogen peroxide H2O2H2O2H2O2H2O2 6Tetrachloromethane CCl 4 7Ethane C2H6C2H6C2H6C2H6 8Ethene C2H4C2H4C2H4C2H4

Expanding the octet 25/10/2015 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 electrons The elements that do this that you need to be aware of are Gp V – P, As Gp VI – S, Se, Te Gp VII – Cl, Br, I, At

Reducing the octet 25/10/2015 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.

25/10/2015 H H H N C OO

Dative bond

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Metallic bonding 25/10/2015