AQA GCSE Chemistry C2 1.3 Chemical Bonding

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C2 1.3 Chemical Bonding

Elements form compounds by sharing, gaining, or donating electrons from their shells.

When atoms share electrons, this is covalent bonding.

When atoms transfer (donate or gain) electrons, this is ionic bonding.

In ionic bonding, electrons are lost or gained to make an atom stable- with a 'noble gas' structure. e.g. Sodium (2,8,1) loses an electron to form stable neon (2,8)

However this neon is left with one more positive proton in its nucleus than negative electrons on the outer shells, meaning that the sodium is now a positively charged sodium ion: Na+ [2,8]+

The opposite occurs if an atom gains an electron- with one more negative electron than positive protons, an atom such as chlorine (2,8,7) becomes negatively charged: Cl- [2,8,8]-

Elements from Group 1 and Group 7 will react together to form full shells.

'Dot and Cross Diagrams' can be used to represent ionic bonding- remember this is when electrons are lost or gained, not shared.

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C2 1.4 Ionic Bonding

Due to opposing charges, ions in ionic bonding are held together by enourmously strong electrostatic forces of attraction that act equally in all directions.

We call this arrangement of ions a "giant structure" or a "lattice".

The ions in these structures pack together very neatly, creating very regular giant structures.

Multiple electrons are sometimes lost or gained to form the noble gas structure.

Below, a dot and cross diagram is being used to display the rection between Magnesium [2,8,2] and oxygen [2,6] to form Magnesium oxide [2,8]^2+ and [2,8]^2-. The magnesium ion has donated to electrons to the oxygen ion, so that they both have full outer shells.Groups 2 and 6 also react to form ionic bonds and full outer shells. (http://www.bbc.co.uk/staticarchive/935a9668fd093be64efabb18ca7fcf192d83c08e.gif)

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C2 1.5 Covalent Bonding

Ionic bonds form between a metal and non-metal, whereas covalent bonds are formed between  two non-metals.

Covalent bonds occur when neither atom can donate or gain an electron- so they share!

Sometimes multiple atoms of the same element bond with just one atom of another element, such as to hydrogen atoms bonding with one oxygen to for H2O, or water.

Covalent bonds can also be represented with dot and cross diagrams:

(http://www.bbc.co.uk/staticarchive/bdd7c0044c8cb249325cabd9eb190b204dcad6c6.gif) This is hydrogen and oxygen sharing electrons to form water.

Most covalently bonding substances are made of small molecules, however, some contain huge numbers of atoms bonded together to create "giant covalent structures". An example of this is diamond: each carbon has four covalent bonds with its neighbours, forming a "lattice".

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C2 1.6 Bonding in Metals

Metals are also "giant structures", consisting of a lattice of metal atoms in regular layers.

The outer electrons (delocalised electrons)  in a metal structure can move freely between atoms and so form a "sea of electrons" around the positively charged metal ions.

There are strong electrostatic attraction between these negative electrons and the positive metal ions bonds the metal together.

Metals are made of small crystals called "grains", which join at "grain boundaries".

Metals such as steel are "galvanised" by zinc to protect from rusting- in this case metal crystals are visible on the surface of the steel.

(http://www.chemhume.co.uk/ASCHEM/Unit%201/Ch3IMF/Images%203/sea_of_electrons.jpg) This is the structure of metals, with ions and electrons.

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