Chemistry

What is an element

A substance that consists of only one type of atom and cannot be broken down into anything simpler by chemical means

How many types of elements exist

There are 118 elements discovered

What is an atom

It is the smallest piece of an element that exist

What is a compound

Atoms of different elements combined together

What are the features of chemical reactions

• They are broken up or formed

• Measurable change

• At least one new substance is created

• No new atom is created or destroyed

How many atom models have been made

4

List the atom models discovered

The Dalton’s model, the Thomson’s plum pudding model, the Rutherford’s nuclear model and the modern model

Give a brief history of the Dalton’s model

• In 1803, John Dalton first suggested that all matter is made of atoms and that atoms cannot be split.

• Scientists improved Dalton’s original model of an atom with the discovery of sub-atomic particles.

Give a brief history of the Thomson’s model

• In 1897, an English physicist called J. J. Thomson discovered electrons.

• He modelled the atom as a 'plum pudding' - a ball of positive charge (dough), with negatively charged electrons (currants) mixed in with the 'dough'.

Give a brief history of the Rutherford’s nuclear model

• In 1909, Ernest Rutherford discovered that alpha particles could bounce back off atoms.

• He concluded that an atom's mass is concentrated in the atom's centre. This was called the "nucleus" and it contained positively charged particles called protons.

Give a brief history of the modern model

• Niels Bohr discovered that electrons orbit (fly around) the nucleus at fixed distances.

• In 1932, James Chadwick discovered that some particles in the nucleus have no charge at all. He called them neutrons.

What are the 3 sub-atomic particles

Protons, neutrons and electrons

Features of a proton

• They have a relative charge of +1

• They are found in the nucleus

• An element’s atomic number is the number if protons it has

• They have a relative atomic mass of 1

Features of an electron

• They have a relative charge of -1

• They are found fixed in orbits around the nucleus

• In any atom, the total number of negative electrons = the number of positive protons (atoms have no overall electric charge)

• They have a relative atomic mass of 1/2,000, which is approximate to 0

Features of a neutron

• They have a relative charge of 0, they are neutral

• Like protons, they are found in the nucleus

• They have a relative atomic mass of 1

• They have the same mass as protons but have no charge