Atomic Structure

Atomic Structure

Basic Information

  • All matter is made up of atoms, which are the smallest particles of a chemical element that can exist.

  • An atom consists of a central nucleus surrounded by electrons.

  • The nucleus contains two types of particles: protons and neutrons.

  • The number of protons in an atom determines its atomic number. This defines the type of element the atom represents.

Subatomic Particles

  • Protons have a positive charge. The number of protons in an atom is unique to each element.

  • Neutrons have no charge (they are neutral). They contribute to the mass of the atom.

  • Electrons have a negative charge and are found in shells orbiting the nucleus. Their number can vary within an atom of a given element.

  • Protons and neutrons have roughly the same mass, much larger than that of an electron. For practical purposes, the mass of an electron is often assumed to be negligible.

Atomic Models

  • The Bohr model of an atom represents it as a central nucleus containing protons and neutrons, with electrons in energy levels around it.

  • The more modern quantum mechanical model represents electron locations as ‘clouds’ or ‘orbitals’ where the electron is likely to be.


  • Isotopes are atoms of the same element (with the same number of protons) but with different numbers of neutrons. This gives them different atomic masses.

  • Isotopes can be unstable, leading to radioactive decay.

Keywords to Remember

  • Atomic.mass: The number of protons and neutrons in an atom.

  • Ion: An atom or group of atoms carrying a positive or negative charge due to loss or gain of electrons.

  • Ionisation: The process of forming ions by gaining or losing electrons.

Remember these key points and keep working on your understanding of atomic structure. It forms the foundation for many other topics in chemistry. Discuss any problems with your teacher or classmates.