Valence Electrons & Ionic Compounds (College Board AP® Chemistry)

Study Guide

Test yourself
Martín

Written by: Martín

Reviewed by: Stewart Hird

Valence electrons

  • Valence electrons are the electrons present in the outermost shell of an atom

  • Valence electrons dictate an atom's reactivity and ability to form bonds

  • The number of valence electrons can be obtained from the electron configuration of an atom

The Beryllium Atom

beryllium-electron-configuration-and-valence-electrons

Beryllium electron configuration and valence electrons

  • The interactions between the valence electrons and nuclei of elements determine if two elements are likely to form a chemical bond

  • There are two types of chemical bonds depending on the elements that take part in the bonding process: ionic bond and covalent bond

    • An ionic bond occurs between a metal and a nonmetal

    • A covalent bond occurs between two nonmetals

Ion Charges & Valence Electrons

Valence Electrons and the Periodic Table

  • Elements in the same group (columns) of the periodic table have the same number of electrons in their valence shell

  • The valence electrons determine the chemical behavior

  • As you move across a period from left to right, without counting the transition metals, the number of valence electrons increases by one

Formation of Ions

  • Ions are atoms that have lost or gained electrons

  • Atoms form ions to achieve the electron configuration of their closest noble gas

  • Noble gasses have a stable electron configuration because of their full outer shell

  • Atoms lose electrons to form cations

    • Since a cation has more protons than electrons, it has a positive charge

    • Cations are formed by elements metals which have few valence electrons

Sodium Atom Becoming a Sodium Ion

sodium-atom-and-ion

Formation of positively charged sodium ion - sodium loses 1 electron to become a sodium ion

  • Atoms gain electrons to form anions

    • Since an anion has less protons than electrons, it has a negative charge

    • Anions are formed by non-metals which are elements that lack a few electrons

  • The electrostatic attraction between a positive ion (cation) and a negative ion (anion) is defined as an ionic bond

Chlorine Atom Becoming a Chloride Ion

chlorine-atom-chloride-ion

Formation of negatively charged chloride ion - it gains 1 electron to become a chloride ion

Common ions and the Periodic Table

  • The periodic table can help you to identify the typical charges of cations or ions

  • Elements in Group 1 tend to lose their lonely electron from their valence shell, therefore, the common charge for all the elements is 1+

    • E.g. Sodium (Na) tend to form Na+ cation

  • Elements in Group 2 tend to lose two electrons from their valence shell, therefore, the common charge for all the elements is 2+

    • E.g. Magnesium (Mg) tend to form Mg2+ cation

  • Elements in the Group 3 (skipping the transition metals) tend to lose three electrons from their valence shell, therefore, the common charge for all the elements is 3+

    • E.g. Aluminum (Al) tend to form Al3+ cation

  • Elements in the Group 5 (skipping the transition metals) tend to gain three valence electrons, therefore, the common charge for all the elements is 3-

    • E.g. Nitrogen (N) tend to form N3- anion

  • Elements in the Group 6 (skipping the transition metals) tend to gain two valence electrons, therefore, the common charge for all the elements is 2-

    • E.g. Oxygen (O) tend to form O2- anion

  • Elements in the Group 7 (skipping the transition metals) tend to gain one valence electron, therefore, the common charge for all the elements is 1-

    • E.g. Fluorine (F) tend to form F- anion

  • Atoms in Group 4 tend not form ions, therefore it is not possible to form ionic compounds with those elements

Examiner Tips and Tricks

From Group 1 to Group 3, the positive charge is equal to: charge = number of group. From Group 5 to Group 7, the negative charge is equal to: charge = number of group - 8. This trick works only if the groups of the transition metals are not numbered

Last updated:

You've read 0 of your 5 free study guides this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Martín

Author: Martín

Expertise: Chemistry Content Creator

Martín, a dedicated chemistry teacher and tutor, excels in guiding students through IB, AP, and IGCSE Chemistry. As an IB Chemistry student, he came from hands-on preparation, focusing on practical exam techniques and rigorous practice. While at Universidad San Francisco de Quito, his academic journey sparked a passion for computational and physical chemistry. Martín specializes in chemistry, and he knows that SaveMyExams is the right place if he wants to have a positive impact all around the world.

Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.