ATOMS AND ELEMENTS
Everything is made of atoms
Everything is made of tiny lumps of matter called atoms; atoms are made up of even smaller particles. Structure of atoms

Protons, electrons and neutrons
Electrons are whizzing around the central nucleus.
Each electron, and each proton in the nucleus, carries an electrical charge.
Electrons carry a negative charge.
Protons carry a positive charge.
Neutrons have no charge as they are neutral.
The electrons have a lot of energy and move rapidly, they have an electrical attraction to protons in the nucleus.
So, the orbit of an electron is the balance between its fast movement and the electrical attraction pulling it towards the nucleus.
Protons in the nucleus repel each other electrically.
The protons in the neutrons in the nucleus are held together by an even more powerful force called the strong nuclear force. This force easily overpowers electrical repulsion. How small is an atom?
Extremely small, less than one millionth of a millimetre in diameter. Atoms and elements
A chemical element is a substance made entirely of identical atoms.
The atoms of each element are all the same as each other.
The atoms of one element are different to the atoms of another element. This is because they have different numbers of protons, electrons and neutrons. How are the atoms of different elements different?
The atoms of each element have a certain number of protons, electrons and neutrons.
Number of protons = Number of electrons = Atomic number. Balance of electrical charges
Remember it is the protons and the electrons which carry an electrical charge. Since the numbers of electrons and protons are always equal, they cancel out and so atoms have no overall electrical charge. The periodic table of elements Why is the table such an odd shape?
The periodic table has this shape so that elements that are similar to each other are under each other, or in groups and blocks. It is called periodic because it has patterns that re-occur in a regular pattern. The mass of atoms
To find relative mass, we simply compare how many particles each atom has within its structure. Mass of protons, neutrons and electrons
The mass of an atom depends on how many particles it has within its structure.
It turns out that protons and neutrons are about the same mass. This amount of mass is called the atomic mass unit or amu.
The relative mass of an atom can be found by simply adding together the number of protons and neutrons in the nucleus. Atomic mass number
Atomic mass number = Number of protons + Number of neutrons (this must be a whole number) Mass numbers and R.A.M.
The mass number for an individual atom is always a whole number.
The relative atomic mass (RAM) listed on the periodic table is usually not. The RAM shown in the periodic table is the average of these slightly different mass numbers. History of our understanding of atoms
- Democtritus
He decided that matter was probably made of ultimate units of matter. He called tem atomus, which means something that cannot be divided. – he discovered this using a magic knife to cut a substance into smaller and smaller substances.
- John Dalton
He reasoned that each element must have unique atoms which react and combine with each other in simple ratios. – he realised this via chemical reaction experimentation.
- Joseph Thomson
Studying the mysterious “cathode rays”, Thomson identified a small particle with a negative electrical charge. -> He discovered the electron.
He proved that exactly the same particles (electrons) were present in every kind of atom tested. This suggested that all atoms contain these small negative charges.
If every atom contains negative particles, there must be a positively charges material in every atom to balance the electrical charge.
Thomson proposed the “plum-pudding” model in 1904. He suggested that each atom was a solid ball of positively-charged material with