Atomic structure: -
The nucleus of an atom contains protons and neutrons. Around the nucleus are electrons arranged in shells.
All atoms of the same element have the same number of protons and neutrons. An atom has no overall electrical charge.
The masses of protons and neutrons and electrons are incredibly small. Atomic mass units are used to express their mass relative to one another – relative masses.
Relative masses and charges of sub atomic particles; elements arranged in the periodic table in order of atomic number; symbol, mass number and atomic number of each element.
During a chemical reaction, the elements remain the same. Only electrons are involved, they are usually transferred or shared between atoms. A small amount of energy is either taken in or given out.
In nucluear reactions, nuclei of atoms either split or join together. In both cases, huge amounts of energy are released:
In nuclear fission, the nucleus of one atom of a large element splits to give two nuclei of smaller elements.
In nuclear fusion, the nuclei of two small atoms join together to form a new element.
Electronic structure: -
Electrons are arranged in shells. The innermost shell hold up to two electrons, the second up to eight. Each shell represents a different energy level. The innermost shell has the lowest energy level. Electrons occupy the lowest available energy levels.
Atoms with a full outer shell are considered to be stable and unreactive. When an atom reacts, it gains, loses