Bonding and Molecules
Atoms rarely travel alone. They join together into molecules and compounds, and the way they join, the chemical bond, decides almost every property of the material that results. Understanding bonding explains why salt is brittle, why water sticks together, and why metals conduct electricity.
This lesson covers why atoms bond and the main types of bonds you will be tested on.
A chemical bond is the force that holds atoms together. Atoms bond to fill their outer electron shells and become more stable. In an ionic bond, electrons are transferred from one atom to another; in a covalent bond, electrons are shared; in a metallic bond, electrons move freely among many metal atoms. A molecule is two or more atoms bonded together.
Why do atoms form bonds?
Atoms bond to reach a stable arrangement of electrons, usually a full outer shell. Elements with nearly full or nearly empty outer shells are the most reactive, because they have the most to gain by trading or sharing electrons. Noble gases, whose shells are already full, almost never bond at all. That drive toward a full outer shell is the reason behind every bond.
What is an ionic bond?
An ionic bond forms when one atom transfers electrons to another. The atom that loses electrons becomes a positive ion, the atom that gains them becomes a negative ion, and the opposite charges attract. Table salt, sodium chloride, is the classic example: sodium hands an electron to chlorine, and the two ions lock together. Ionic compounds tend to be brittle solids with high melting points, and they conduct electricity when dissolved in water.
What is a covalent bond?
A covalent bond forms when atoms share electrons instead of transferring them. This usually happens between nonmetals. Water is a covalent molecule: each hydrogen shares electrons with oxygen. Covalently bonded substances form distinct molecules and often have lower melting points than ionic compounds. Many everyday materials, from oxygen gas to sugar, are held together by covalent bonds.
| Bond type | What happens to electrons | Example |
|---|---|---|
| Ionic | Transferred (one atom to another) | Sodium chloride (salt) |
| Covalent | Shared between atoms | Water |
| Metallic | Shared freely among many atoms | Copper metal |
What is a metallic bond?
In a metallic bond, the outer electrons are not tied to any single atom. They form a shared “sea” of electrons that flows around the metal atoms. This loose, shared arrangement explains why metals conduct electricity and heat so well and why they can be bent and hammered into shape without shattering.
Watch: A Short Video Lesson
StudyPass walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for bonding questions
- Ask what the atoms are trying to do: fill their outer electron shells.
- Metal plus nonmetal usually means an ionic bond (electrons transferred).
- Nonmetal plus nonmetal usually means a covalent bond (electrons shared).
- Many metal atoms together means metallic bonding (a sea of electrons).
- Match the properties: brittle and high-melting suggests ionic; distinct molecules suggests covalent; conductive and bendable suggests metallic.
Practice questions
- Why do atoms form chemical bonds?
- In an ionic bond, what happens to the electrons?
- Water is held together by which type of bond?
- Which bond type explains why metals conduct electricity?
- What is a molecule?
- True or false: noble gases bond readily with most elements.
Answers:
- To fill their outer electron shells and become more stable.
- They are transferred from one atom to another, creating positive and negative ions.
- Covalent bonds (shared electrons).
- Metallic bonding, with its free-moving sea of electrons.
- Two or more atoms bonded together.
- False. Noble gases have full outer shells and rarely bond.
Where this fits
Bonding depends on electrons gained and lost, so it grows out of atomic number, isotopes, and ions and an element’s place on the periodic table. Bonded atoms make up the compounds and mixtures you study next. All topics live on the ASVAB General Science Learning Hub.
Recommended Prep Books
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