Chemistry - EDEXCEL IGCSE - Chemistry of the elements (part 1)

CHEMISTRY OF THE ELEMENTS (PART 1)

The Periodic Table

Metals - 

1. High melting and boiling points
2. Good conductors of electricity and heat
3. Have oxides that tend to be basic

Non-metals -

1. Generally have lower melting and boiling points
2. Don’t usually conduct electricity
3. Form acids with oxides. Sometimes they can also be neutral

Elements in the same group have similar chemical properties because their atoms have the same number of electrons in their outermost energy shell/level. Therefore, the atoms give or take the same number of electrons during a reaction if they are in the same group. This means that atoms in the same group have similar chemical properties.

Noble gases (group 0) are inert gases that generally do not react very well. This is because their outermost shell is full, they, therefore, do not need to take or give electrons as they are are already at their most stable configuration. 

Group 1 Elements:

All group 1 elements react with water to form hydrogen and a metal hydroxide solution. The reaction is also exothermic meaning it gives off heat.

Lithium - when placed in water the metal reacts with the water. Because the hydrogen released is not released symmetrically, the metal moves around and over the water. A white trail is formed of LiOH.

Sodium - the same reaction as lithium except that it melts as the heat produced is enough to melt sodium.

Potassium - enough heat is produced to burn the hydrogen released with a lilac flame.

Rubidium, Caesium - these metals are so reactive that the reaction created is explosive.

As you can see the further down you go in terms of the period of the group 1 elements (i.e. how big the element is), the higher the reactivity. This is because as the atoms of the elements become bigger, the electron in the outer shell moves further away, this means that it is easier for it to escape from the attractions of the protons in the nucleus. This, therefore, means reaction occurs faster.

Group 7 - the Halogens:

Properties:

1. Boiling and melting point increases as the period goes up
2. Salt - producing
3. Diatonic
4. Poor conductors
5. Colour becomes darker as the period goes up

Hydrogen chloride gas is an anhydrous compound in the gas state while hydrochloric acid is an aqueous solution of hydrogen chloride

Hydrochloric acid is also acidic because of the H⁺ ions in the water.

Hydrogen chloride is an ionic compound meaning it only dissolves in polar solvents such as water and not in organic substances such as methylbenzene. Dissociation of HCl because of the water creates an acidic solution as there will be H⁺ ions in the water.

As the period increases for the halogens, the reactivity decreases. Because of this, the larger the group 7 atom, the less volatile it is. This is why iodine is solid while fluorine is a gas. Also, as the period decreases, the colour lightens. 

Adding a solution of chlorine to a potassium chomped with a less reactive element (i.e. lower period) will cause the solution to become coloured as the least reactive element with be displaced.

e.g. 2KBr + Cl₂ —> 2KCl + Br⁺

These reactions are called redox reactions.

Oxygen and Oxides:

Nitrogen - 78.1%

Oxygen - 21%

Argon - 0.9%

CO₂ - 0.04%

Proving the volume of O₂ in the air:

With Copper:

1. Oxygen reacts with copper
2. Attach a syringe with 100cm³ of air to a tube packed with copper
3. Use a bunsen burner to heat the copper, allowing it to react with oxygen faster
4. Move the burner as you do to make sure only fish copper is burnt
5. Keep on doing this until the copper stops turning black
6. See how much of the air has been used and take it as a percentage

With the rusting of iron:

1. Place the iron wool in an inverted test tube filled with air and then place it in water
2. Mark the original level of water in the test tube with a rubber band
3. Wait a week for the iron to react with the oxygen and water (rust)
4. Mark the higher water level with another rubber band
5. Fill the tube up to the rubber band and pour the water into a measuring cylinder. Do this for the second rubber band level too
6. First volume / second volume = amount of oxygen as a %

Oxygen from hydrogen peroxide:

This is a catalytic decomposition reaction with manganese (IV) oxide as the catalyst. The oxygen is collected through the displacement of water.

Oxygen burning in…

1. Magnesium - burns with a bright white flame, with white powdery ash (MgO), which when dissolved forms a basic solution.
2. Carbon - burns with a yellow flame produces colourless CO₂ gas, which the dissolved forms an acidic solution.
3. Sulphur - burns with a bright blue flame, produces colourless sulphur dioxide, which when dissolved forms an acidic solution.