Basic Atom Structure

  • An atom is the smallest constituent unit of ordinary matter.
  • Each atom is composed of protons, neutrons, and electrons.
  • Protons and neutrons make up an atom’s nucleus.
  • Electrons orbit around the nucleus in a cloud-like formation.
  • The atomic number of an atom is the number of protons in its nucleus.
  • The mass number of an atom is the total number of protons and neutrons in its nucleus.

Atomic Charge

  • Protons carry a positive charge, electrons carry a negative charge, and neutrons are neutral.
  • In a neutral atom, the number of protons and electrons are equal, balancing out the charge.
  • Ions are atoms where the number of protons and electrons are not equal, resulting in a net charge.

Elements and Isotopes

  • Elements are defined by the number of protons they contain, eg. all atoms of Oxygen have 8 protons.
  • Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons, resulting in different atomic masses.
  • Examples of isotopes are Carbon-12, which has 6 neutrons and Carbon-14, which has 8 neutrons. Both are isotopes of carbon.

Structure of an Electron

  • Electrons occupy energy levels also known as shells.
  • The first shell can hold up to 2 electrons, and the subsequent shells can hold up to 8 electrons.
  • Electrons will always fill up the lower energy levels first before moving to the higher energy levels.

Bohr Model of an Atom

  • The Bohr model is a simple way of visualising an atom’s structure.
  • In this model, the nucleus is at the centre, and the electrons circle around it in fixed orbits, or energy levels.
  • Each energy level can hold a specific number of electrons: 2 in the first level, 8 in the second, and 8 in the third.
  • If an atom has more than 18 electrons, additional ones will populate the fourth energy level, which can hold up to 18 electrons.