Study notes for Unit 2 Topic 1 - Ionic Bonding for Chemistry Edexcel A Level 2015. Focusing on what ionic bonding is, how this type of bonding is formed and why, the various factors affecting ionic bonding and the trends in ionic radii, and physical properties of ionic compounds.
Recap:
● When electrons are transferred, ions are formed.
● They can be positive cations or negative anions.
● Simplest ions are single atoms which have achieved a full outer shell.
● Elements will lose or gain electrons to get the full outer shell, and will
therefore form an ion with the same charge (e.g. Mg will lose 2
electrons and become Mg2+).
Ionic Bonding:
● This is the strong electrostatic attraction between oppositely charged
ions.
● The stronger the electrostatic attraction, the stronger the ionic bond.
● When oppositely charged ions form an ionic bond, you get an ionic
compound.
● The positive and negative charges balance exactly, so the total overall
charge of an ionic compound is zero.
Factors affecting ionic bonding:
1. Ionic Radius - smaller ions can pack more closely together than larger
ions, and since electrostatic attraction gets weaker with distance, small
and closely-packed ions have stronger ionic bonding than larger ions,
and will also have higher melting/boiling points.
2. Ionic Charge - the greater the charge on an ion, the stronger the ionic
bond and therefore the higher the melting/boiling point.
Trends in ionic radii:
1. Ionic radius - increases down a group, as extra electron shells are
added.
2. Isoelectronic ions - these are ions of different atoms with the same
number of electrons (e.g. O2- and Na+). The ionic radius of a set of
isoelectronic ions decreases as the atomic number increases. This is
because the electrons are more strongly attracted to the nucleus with
more protons, so they are pulled in a little.
Dot-and-cross diagrams:
● Show the arrangement of electrons in an atom or ion, and they can also
show where the electrons in a bond originally came from.
● Usually only the outer electrons are shown.
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