Chemical Bonding

Grade 11 · Science · Study Guide

Discover how and why atoms bond together, from electron transfer in ionic bonds to sharing in covalent bonds and the electron sea of metallic lattices.

Chemical bonding is the force that holds atoms together in compounds. Atoms bond because doing so lowers their energy — most atoms are most stable when their outermost shell is full, a concept called the octet rule. There are three primary bond types: ionic, covalent, and metallic.

Ionic bonds form between atoms with very different electronegativities — typically a metal and a nonmetal. The more electronegative atom strips electrons from the other, creating oppositely charged ions that attract electrostatically. Sodium chloride (NaCl) is the classic example: Na loses one electron to become Na⁺, Cl gains it to become Cl⁻. Ionic compounds form crystal lattices, have high melting points, and conduct electricity when dissolved or melted.

Covalent bonds form between nonmetals that share pairs of electrons. Single bonds share one pair; double bonds share two pairs; triple bonds share three. In polar covalent bonds, the more electronegative atom pulls electron density toward itself, creating partial charges (δ+ and δ−). Water is polar covalent because oxygen's high electronegativity pulls electron density away from hydrogen.

VSEPR theory (Valence Shell Electron Pair Repulsion) predicts molecular geometry. Electron pairs arrange themselves to maximize separation, giving molecules characteristic shapes: linear (CO₂), bent (H₂O), trigonal planar (BF₃), tetrahedral (CH₄), trigonal pyramidal (NH₃). Shape determines polarity and reactivity.

Metallic bonds involve delocalized electrons — an electron sea surrounding positive metal cations. This explains metals' electrical and thermal conductivity, malleability, and luster.

Key terms

Ionic Bond

Electrostatic attraction between oppositely charged ions formed by electron transfer from a metal to a nonmetal.

Covalent Bond

A bond formed by sharing one or more pairs of electrons between two nonmetal atoms.

Electronegativity

Measure of an atom's tendency to attract shared electrons; increases across a period, decreases down a group.

Polar Covalent Bond

Covalent bond where electrons are shared unequally due to electronegativity difference.

VSEPR Theory

Predicts molecular geometry based on minimizing repulsion between electron pairs around a central atom.

Lewis Structure

Diagram showing valence electrons as dots (lone pairs) or lines (bonds) around atoms.

Metallic Bond

Attraction between delocalized electrons (electron sea) and positive metal cations in a metal lattice.

Octet Rule

Atoms tend to form bonds to achieve 8 valence electrons, mimicking noble gas configuration.

Practice questions

1. Which type of bond involves the transfer of electrons from one atom to another?

   1. Covalent bond
   2. Metallic bond
   3. Ionic bond
   4. Hydrogen bond
   Show answer

   Ionic bonds form when a metal transfers electrons to a nonmetal, creating oppositely charged ions.

2. What molecular geometry does water (H₂O) have according to VSEPR theory?

   1. Linear
   2. Trigonal planar
   3. Bent
   4. Tetrahedral
   Show answer

   Oxygen has 2 bonding pairs and 2 lone pairs. Lone pairs compress the bond angle to ~104.5°, giving a bent shape.

3. In metallic bonding, valence electrons are ______, forming a sea of electrons around positive metal cations.

   Show answer

   Delocalized electrons are not associated with any particular atom and move freely, giving metals their conductivity.

4. A bond between two atoms with an electronegativity difference of 1.5 is best described as:

   1. Nonpolar covalent
   2. Polar covalent
   3. Ionic
   4. Metallic
   Show answer

   Differences of 0.4–1.7 indicate polar covalent bonding; 1.5 falls squarely in this range.

5. How many valence electrons does nitrogen (N) have in a Lewis structure?

   1. 3
   2. 5
   3. 6
   4. 8
   Show answer

   Nitrogen is in Group 15 and has 5 valence electrons. In NH₃, it forms 3 bonds and retains 1 lone pair.

Fun facts

• Diamond and graphite are both pure carbon, yet one is the hardest natural substance and the other is slippery enough to be used as a lubricant — the difference is entirely in bonding structure.
• Fluorine is the most electronegative element (3.98 on the Pauling scale), which is why HF is so reactive it can etch glass.
• The metallic electron sea explains why metals can be hammered into sheets (malleability) — cation layers slide through the fluid electron sea without bonds breaking.

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