NON-METAL + NON-METAL

When two non-metals react, they gain noble gas electron arrangements by sharing electrons.

Most covalent bonds consist of small molecules. e.g. SO₂, NH₃

The forces inside these molecules (Intermolecular) are weak, but the forces between the bonds are strong.

The interparticle forces are easy to overcome by boiling or melting. The forces are so weak in simple molecular substances, they are used in gases at room temperature, low b.p. liquids and low m.p. solids.

Simple molecular substances do not conduct electricity when solid, liquid or in aqueous solution because they do not contain any mobile charged particles.

Sometimes when simple molecules dissolve in water, they either split apart to form ions or react with the water to form ions.

Simple molecular substances are often insoluble in water. They are often soluble in Non Polar e.g. Benzene.

Simple molecular elements and compounds tend to be dull and brittle. Most molecules are small, but some are covalently bonded substances which have giant structures called

Macro Molecules e.g. Diamond and graphite are allotropes of Carbon.

Ionic compounds also have giant structures. This time the lattice consists of a regular arrangement of oppositely charged ions in alternate positions. This extends infinitely in all directions and produced a "crystalline" appearance of ionic solids, i.e.. smooth shiny faces and sharp edges, e.g. Sodium Chloride.

We see that each Sodium ion has 6 Cl ions as nearest neighbors and vice versa. The crystals are held together by strong electrostatic forces (+ and -)

Ionic solids have high melting points. To melt any solid it is necessary to overcome forces between particles by heat energy so that the particles can move more randomly. Interparticle forces are strong in ionic compounds and so a lot of heat energy is required.

Ionic compounds will conduct electricity when dissolved in water because ions are free to move around.

We remember that an electric current is a flow of electrons OR of ions in an electrolyte. An electrolyte is a liquid which conducts electricity by the movement of ions.

An ionic compound will not conduct electricity when solid because the ions are not free to move to the electrodes.

Since the forces between ions are strong, ionic solids are hard and strong. However, if a deforming force is applied, ions of both charges are brought together.

+ - + - + - +
- + - + - + -

Ions repel and break the crystal

Ionic compounds are usually soluble in water. The ions break apart and take up more space between particles. We say the water is a Polar solvent as it has a strong attraction for ions.

METAL + METAL

Metals are malleable (They can be hammered into shape) and ductile (They can be pulled into wires). This is because the layers of cations slide across one another, given sufficient force, but are still held together by the attraction force between them and the delocalised electrons.

Metals are also good conductors of heat. The delocalised electrons are not restricted to vibration, they can move through the lattice. If one end of a piece of metal is heated, the nearby electrons are given energy, and because of their low mass, they get to a high speed. Energy is transmitted through the lattice, by the fast moving electrons and their collisions.

Metals are also good conductors of electricity, and that an electric current in a metal, is the flow of electrons. When a voltage is applied, electrons are pushed into one end by a power source. This becomes part of the lattice, and the electrons move in the form of a shunting process. Electrons which were part of the delocalised pool, leave the metal at the other end.

Metals can conduct electricity because they contain "Free Electrons" or "Mobile Electrons".

Metals are also shiny when freshly cut or polished.

Zinc metal powder and Iodine crystal were mixed thoroughly in a small beaker. In a fume cupboard, drops of water were added making a vigorous exothermic reaction. The heat of the reaction was sufficient to vaporize some of the Iodine as purple fumes were seen. Next 100 cm³ of water was added to make a solution which was then filtered. We poured the filtrate into a voltmeter and passed a direct current through it. Bubbles were seen, along with a pale grey spongy solid at the negative electrode and a dark grey solid at the positive electrode which dissolved to make the solution brown.

The electrolyte was Zinc Iodide.

When metals react they lose electrons to form positive ions (cations). Zinc forms 2⁺ cations when it reacts. Iodine is in group 7 so it is 1 electron short of a "Noble Gas Electron Arrangement"".

In this experiment, Iodine gains this electron by sharing an electron to form a covalent bond

(I₂ or I-I).

Zn²⁺ I^-₂ or ZnI₂

Like most ionic compounds, Zinc Iodide dissolves in water. The Aqueous solution conducts electricity by the movement of ions. We remember that electrolytes decompose when they carry an electric current. Changes occur at the electrodes because of electron transfers.

AT CATHODE (-)

Zinc ions are attracted and discharged.

Zn²⁺ + 2e^- = Zn (grey Solid)

AT ANODE (+)

Iodide ions are attracted and discharged

2I^- - 2e^- = I₂ (Brown Solution)

Metal + Water = Metal Hydroxide + Hydrogen

Metal + Steam = Metal Oxide + Hydrogen

Lithium - Moves around on the surface with a fizzing noise.

Sodium - Very exothermic, the Sodium is made into a ball.

Potassium - Very exothermic, the hydrogen burns producing a lilac flame

These metals, along with Rubidium and Caesium are kept under paraffin oils to prevent reaction with air and water vapour. They are shiny when freshly cut, but soon become dull due to a reaction with oxygen.

(Group 1 Metal) + Oxygen = (Group 1 Metal)₂0

4(Group 1 Metal) + O₂ = 2(Group 1 Metal)₂0

Group 2 metals are not as reactive as Group 1 metals, but they also become more reactive down the group.

(Group 2 Metal) + Oxygen = 2(Group 2 Metal)O