The Atom

The Basic Structure of an Atom

An atom is made up of protons, neutrons and electrons.
Protons and neutrons form the nucleus, located at the centre of an atom.
Electrons are found in the electron shells, which surround the nucleus.
Protons possess a +1 charge, electrons have a -1 charge, and neutrons do not have any charge, therefore, they are neutral.
The atomic number of an atom, also termed as the proton number, represents the number of protons present in the atom’s nucleus.
The mass number represents the total of protons and neutrons present in an atom’s nucleus.

Isotopes are atoms of an element with different numbers of neutrons, hence differing mass numbers but identical atomic numbers.
The relative atomic mass (Ar) of an element takes into account the existence of isotopes and their relative abundances, and it’s effectively a “weighted average” mass.

The electronic configuration helps us identify the number of electrons in each energy level or shell.
Energy levels accommodate electrons in a structured way: the first energy level contains up to 2 electrons, the second can hold up to 8, and subsequent levels can hold more.
Electrons occupy the lowest available energy level first, known as the Aufbau Principle.

Atoms can lose or gain electrons to attain a full outer energy level, becoming charged particles known as ions.
If an atom gains electrons, it becomes a negatively charged ion, or an anion. Conversely, if it loses electrons, it becomes a positively charged ion, or a cation.

(Consider practising diagrams of atomic structure, electronic configurations and also writing down definitions of key terms in your own words.)