WJEC science

An Atom is the smallest particle in an element.

The atomic number tells us the number of electrons in an atom

The mass number is the number of protons and neutrons in an atom.

Electrons are found in shells. They have a negative charge. The maximum number of electrons in each shell is as follows:

1st shell- maximum of 2 electrons

2nd shell-maximum of 8 electrons

3rd shell- Maximum of 8 electrons

The periodic table was made by Dmitri Mendeleev in1869.

Mendeleev arranged the elements in order of increasing atomic weighs and found that the elements showed similar properties.

He left gaps for undiscovered elements such as gallium.

Rates of reaction can mean either

• The amount of a product made per minute
• The amount of a reactant used up per minute

To speed up a reaction we can

• Increase the temperature
• Increase the surface area
• Increase the concentration of acid
• Increase amount of reactant
• Stir it

Or we can use a catalyst.

Definition- A catalyst speeds up a reaction without getting used up or changing itself.

Crude oil is refined by fractional distillation, in which the oil is seperated into groups of compounds with similar B.P.

The smaller the molecules, the lower their boiling point and the faster and furter they rise up the column.

Fossil fuels- Dead animals and plants

Hydrocarbons are made of HYDROGEN and CARBON only.

The fractions must EVAPORATE and CONDENSE.