2.1 Chemical bonds & types of bonding

Ionic bonding is the electrostatic attraction between positive and negative ions. It is a relatively strong attraction.

● They are held together in a giant lattice. ● It’s a regular structure that extends in all directions in a substance. ● Electrostatic attraction between positive and negative ions holds the structure together.

● High melting and boiling point (strong electrostatic forces between oppositely charged ions) ● Do not conduct electricity when solid (ions in fixed positions). ● Conduct when molten or dissolved in water - ions are free to move.

E.g. Positive: Na+, Mg2+, Al3+, Ca2+, Rb+ Negative: Cl−, Br−, SO42−, NO3−, OH− (chloride, bromide, sulfate, nitrate, hydroxide). Ionic compounds are electrically neutral, i.e. positive and negative charges balance each other.

Reaction of a metal with a non-metal. Electron transfer occurs - metal gives away its outer shell electrons to non-metal. Mg is in Group II, so has 2 available outer shell electrons. O is in Group VI, so can accept 2 electrons to get a full outer shell configuration. Mg becomes Mg2+ and O becomes O2− (oxide).

A covalent bond is a shared pair of electrons between two atoms.

● Do not conduct electricity (no ions) ● Small molecules ● Weak intermolecular forces, therefore: ● Low melting and boiling points

They increase. That causes melting/boiling points to increase as well (more energy needed to overcome these forces).

Polymers are very large molecules (>100s, 1000s of atoms) with atoms linked by covalent bonds. Thermosoftening polymers - special type of polymers; they melt/soften when heated. There are no bonds between polymer chains. Strong intermolecular forces ensure that the structure is solid at room temperature. These forces are overcome with heating - polymer melts.

● Solids, atoms covalently bonded together in a giant lattice. ● High melting/boiling points – strong covalent bonds. ● Mostly don’t conduct electricity (no delocalised e−) ● Diamond, graphite, silicon dioxide.

Forces of attraction between delocalised electrons and nuclei of metal ions.

● High melting/boiling points (strong forces of attraction) ● Good conductors of heat and electricity (delocalised electrons) ● Malleable, soft (layers of atoms can slide over each other whilst maintaining the attraction forces)

Alloys: ● Mixtures of metal with other elements, usually metals ● Different sizes of atoms distorts the layers, so they can’t slide over each other, therefore alloys are harder than pure metals

There are no forces between spheres and atoms, molecules and ions are solid spheres – this is not true

The strength of the forces between the particles of the substance. The nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles the higher the melting point and boiling point of the substance

Pure substances will boil/melt at a fixed temperature. Impure substances will boil/melt over a range of temperatures

● Solid ● Liquid ● Gas