Ion formation

Ion formation


In this lesson, we will learn:
• To understand the reason chemical atoms form ions and the particle that causes ionization.
• To calculate the charge of ions from electron and proton numbers
• To apply knowledge of ion charges to find number of electrons in ions
• To predict an element's stable ions based on the Periodic table


• Atoms are comprised of protons, neutrons and electrons. In a neutral atom, the number of electrons is equal to the number of protons.

• Many elements and substances engage in chemical reactions to obtain a full outer shell of electrons, which involves metal atoms losing electrons to empty their outer shell ('dropping down a shell' in the process) and non-metal atoms gaining electrons to complete a full outer shell.

• These changes in number of electrons changes the overall charge of an atom, if the number of protons and electrons isn't equal in an atom then it becomes a charged atom.


• Chemical reactions only involve outer-shell electrons. They virtually never change the nucleus of an atom.

• To find the charge of an atom or ion, subtract the number of electrons from the number of protons in the particle.

• The electron shell configuration (and therefore its position in the Periodic Table) of an element is strongly related to the stable ions it is able to form – atoms gain or lose a number of electrons to fill their outer shell, which dictates their charge!

Ion formation normally occurs when electrons are transferred from one atom, usually a metal, and donated to another atom, usually a non-metal – this is how ionic compounds are formed.

  • Introduction
    Introduction to ions
    Recall particles and charge.

    Why atoms form ions.

    How atoms form ions.

    Predicting common ions.

  • 1.
    Use information in the Periodic Table to find the number of sub-atomic particles in elements.
    How many electrons are in an atom of the following species?
    i) P
    ii) Ru
    iii) Rb

  • 2.
    Identify atoms and their charge when given the number of sub-atomic particles.
    Identify the element and the charge on the particle described below.
    i) A particle with 50 protons and 52 electrons.
    ii) A particle with 13 protons and 10 electrons.

    i) A particle with 16 protons and 18 electrons.
    ii) A particle with 3 protons and 2 electrons.

  • 3.
    Find out the number of sub-atomic particles when given ions and their charge.
    Find the number of protons and electrons in the following species:
    i) Cr3+^{3+}
    ii) F^-

    i) Sb3+^{3+}
    ii) Zn+^+