Atoms consist of electrons surrounding a nucleus that contains protons and neutrons. Neutrons are neutral, but protons and electrons are electrically charged: protons have a relative charge of +1 and electrons have a relative charge of -1.
Atoms and elements
All substances are made of tiny particles called atoms. An element is a substance that is made of one sort of atom.
An atom has a small central nucleus made up of smaller sub-atomic particles called protons and neutrons. The nucleus is surrounded by even smaller sub-atomic particles called electrons.
Protons and electrons have an electrical charge. Both have the same size of electrical charge, but the proton is positive and the electron negative. Neutrons are neutral.
A summary of the electrical charges in sub-atomic particles
The number of electrons in an atom is equal to the number of protons in its nucleus. This means atoms have no overall electrical charge.
Full chemical symbols
The full chemical symbol for an element shows its mass number at the top, and its atomic number at the bottom.
This symbol tells you that the chlorine atom has 17 protons. It will also have 17 electrons, because the number of protons and electrons in an atom is the same.
The symbol also tells you that the total number of protons and neutrons in the chlorine atom is 35. Note that you can work out the number of neutrons from the mass number and atomic number. In this example, it is 35 – 17 = 18 neutrons.
Writing an electronic structure
***JUST REMEMBER 2, 8, 8, 2*******
Reactions and compounds
New substances are formed by chemical reactions. When elements react together to form compounds their atoms join to other atoms using chemical bonds. For example, iron and sulphur react together to form a compound called iron sulphide.
Compounds usually have different properties from the elements they contain.
Compounds formed from non-metals consist of molecules. The...