Chemical Bonding
Grade 9 · Science · Study Guide
Explore how atoms join together to form compounds through ionic, covalent, and metallic bonds.
Atoms bond with each other to achieve greater stability, usually by attaining a full set of 8 valence electrons — a concept called the octet rule (hydrogen and helium are exceptions, needing only 2). The type of bond that forms depends on the electronegativity difference between the atoms involved — electronegativity is a measure of how strongly an atom pulls shared electrons toward itself.
Ionic bonds form when one atom transfers one or more electrons to another. This typically happens between a metal and a nonmetal. The atom that loses electrons becomes a positively charged cation; the one that gains electrons becomes a negatively charged anion. The strong electrostatic attraction between these opposite charges is the ionic bond. Table salt (NaCl) is a classic example: sodium donates its single valence electron to chlorine, forming Na⁺ and Cl⁻.
Covalent bonds form when two atoms share electrons rather than transfer them. This usually occurs between nonmetals. A single covalent bond shares one pair of electrons, a double bond shares two pairs, and a triple bond shares three pairs. Water (H₂O) and carbon dioxide (CO₂) are common covalent compounds. Metallic bonds are a third type, found in pure metals where electrons flow freely among a lattice of positive metal ions — this 'sea of electrons' explains why metals conduct electricity and heat so well.
| Bond Type | Electron Behavior | Elements Involved | Example |
|---|---|---|---|
| Ionic | Electron transfer | Metal + Nonmetal | NaCl (table salt) |
| Covalent | Electron sharing | Nonmetal + Nonmetal | H₂O (water) |
| Metallic | Electron sea | Metal + Metal | Fe (iron) |
Key terms
- Ionic Bond
- A chemical bond formed by the transfer of electrons from a metal to a nonmetal, creating oppositely charged ions attracted to each other.
- Covalent Bond
- A bond formed when two atoms share one or more pairs of electrons; common between nonmetals.
- Metallic Bond
- Bonding in metals where valence electrons move freely through a lattice of positive ions.
- Electronegativity
- The ability of an atom to attract shared electrons toward itself in a bond.
- Octet Rule
- Atoms tend to gain, lose, or share electrons to achieve 8 valence electrons (a full outer shell).
- Ion
- An atom or molecule with a net electric charge due to gaining or losing electrons.
- Polar Covalent Bond
- A covalent bond where electrons are shared unequally, creating partial positive and negative ends.
Flashcards
- Ionic Bond
- Formed by electron transfer between metal and nonmetal; creates oppositely charged ions.
- Covalent Bond
- Formed by electron sharing between nonmetals; single, double, or triple.
- Octet Rule
- Atoms bond to achieve 8 valence electrons for stability.
- Cation
- Positively charged ion — atom that lost electrons.
- Anion
- Negatively charged ion — atom that gained electrons.
- Electronegativity
- Measure of how strongly an atom attracts bonding electrons.
Practice questions
What type of bond involves the transfer of electrons between atoms?
- Covalent bond
- Metallic bond
- Ionic bond
- Hydrogen bond
Show answer
Answer: Ionic bond
Ionic bonds result from complete electron transfer — the donor becomes a cation (+) and the receiver becomes an anion (-), held together by electrostatic attraction.
Covalent bonds typically form between a metal and a nonmetal.
Show answer
Answer: False
Covalent bonds form between two nonmetals that share electrons. Metal-nonmetal combinations produce ionic bonds.
The tendency of atoms to achieve 8 valence electrons is called the ___ rule.
Show answer
Answer: octet
The octet rule states that atoms are most stable with 8 valence electrons, which drives most chemical bonding behavior.
In an ionic bond, the atom that loses electrons becomes a:
- Anion
- Cation
- Molecule
- Compound
Show answer
Answer: Cation
An atom that loses electrons has more protons than electrons, giving it a net positive charge — it becomes a cation.
Which property of metals is best explained by metallic bonding?
- Brittleness
- Low melting point
- Electrical conductivity
- Transparency
Show answer
Answer: Electrical conductivity
The 'sea of electrons' in metallic bonding allows electrons to flow freely, making metals excellent conductors of electricity and heat.
Fun facts
- Diamond and graphite are both made of pure carbon but have completely different properties because of how their covalent bonds are arranged — diamond is 3D while graphite is 2D layers.
- The water molecule's bent shape, caused by polar covalent bonds, is why ice floats and why life on Earth is possible.
- Electronegativity was first systematized by Linus Pauling, who won two Nobel Prizes — one in Chemistry and one in Peace.
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