SACE Stage 1 Chemistry – Bonding and Structure Notes

Electronegativity is the measure of an atom’s attraction for its outer shell (valence) electrons.

Most atoms have a neutral charge, as the positive charge of the protons cancel out the

negative charge in the electrons.

However, when atoms (or groups of atoms) gain or lose electrons, they have an

overall positive or negative charge, making them an ion.

If an atom loses electrons, there are now more protons, and thus it becomes a positive

ion.

If an atom gains electrons, there are now more electrons, and thus it becomes a

negative ion.

Metals tend to lose electrons in bonding (they have low electronegativity).

Non-metals tend to gain electrons in bonding (they have high electronegativity).

Electrons tend to exist in pairs. This seems unlikely since it seems that they will repel

each other. However, they can do so because they spin in opposite directions.

Atoms which have either 8 electrons in their outer shell or a full outer shell are more

stable than other arrangements.

This is why the Noble Gases (in the 8th group) do not react easily; because they have

either 8 electrons in their outer shell, or because their outer shell is full (eg. Helium

has 2 electrons = full outer shell)

High volatility refers to substances which do not conduct electricity in any state.

They have both low melting points and low boiling points.

Substances which have low volatility have both high melting points and high boiling

points.

There are three types of low volatility;

Electrical conductivity in the solid state which means that they will conduct

electricity both when they are solid or molten,

Electrical conductivity in the molten state which means that they will not conduct

electricity as solids, but will when molten,

No conductivity in molten state which means that they do not conduct both as a

solid or molten.

Although high volatility and the last type of low volatility (no conductivity in molten

state) both do not conduct electricity, there is a difference.

Substances with high volatility have low melting and boiling points, whereas ‘no

conductivity in molten state’ has high melting and boiling points.

So to summarize, substances with high volatility have low melting/boiling points

And substances with low volatility have high melting/boiling points

There are three types of bonding between atoms: Ionic, which happens between a non-

metal and metallic element, Covalent, which happens between two or more non-

metals, and Metallic, which only happens between metals.

Ionic Bonding involves non-metals bonding with metals. Metals form positive ions

(they lose electrons) and non-metals form negative ions (they gain electrons).

Because positive and negative ions attract each other, they then bond together in what

is called an ionic bond.

Ionic bonds do not show any charge when they are written out in their chemical

formulae, as the positive charges cancel out the negative charges.

If we had NaCl (Sodium chloride), the lattice would feature 6 Cl- around one Na+ . Four

Cl’s would be around each side of the Na, and two others would be on the front and

back respectively.

Because this lattice features ionic bonds (which are equal with a neutral charge), there

are also 6 Na’s around each Cl.

So to summarise, Ionic bonding is the electrostatic force of attraction between the

positive and negative ions in the ionic lattice.

Ionic substances have both high melting points and high boiling points.

When in their ionic lattice, they are rigidly held in place and thus cannot change shape.

The only movement is a slight vibration where the ions return to their original place

afterwards.

As a result, they do not conduct electricity as solids because the ions are held in place

and cannot conduct.

However, when melted, they will conduct electricity because the strong forces

within the ionic lattice have been broken, and the ions can move around in any

direction.

Ionic substances have high melting points and high boiling points.

An ionic bond is defined as the electrostatic forces of attraction between the positive

and negative ions.