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Bonding

Ionic, Covalent, Metallic & Properties

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Learning Objectives

Explain ionic bonding and formation

Understand covalent bonding mechanisms

Describe giant covalent structures

Explain metallic bonding

Link structure to properties

Predict properties from bonding type

Introduction to Bonding

Chemical bonding holds atoms together in compounds through electrostatic forces.

Ionic Bonding

Definition: Electrostatic attraction between oppositely charged ions formed by electron transfer.

Metal atom loses electrons → Cation (+)
Nonmetal atom gains electrons → Anion (−)
Opposite charges attract → Ionic bond forms

Ionic Compound Properties

Melting point: HIGH (strong electrostatic forces)
Boiling point: HIGH
Conductivity: Conducts when molten or dissolved (free ions)
Solubility: Often soluble in polar solvents (water)
Hardness: Generally brittle crystals
State: Solids at room temperature

Covalent Bonding

Definition: Shared pair of electrons between two atoms.

Both atoms pull toward shared electron pair
Electrons spend time around both nuclei
May be polar (unequal sharing) or nonpolar (equal sharing)

Molecular Covalent Compounds

Discrete molecules: Fixed number of atoms bonded together

Examples: H₂O, CO₂, Cl₂, NH₃, CH₄

Weak intermolecular forces between molecules

Low melting/boiling points

Giant Covalent Structures

Continuous network: Covalent bonds extend throughout entire structure (no discrete molecules).

Diamond: Each C bonded to 4 other C atoms
Graphite: C atoms in layers (weak bonding between layers)
Silicon dioxide: Continuous SiO₂ network

Diamond vs Graphite

Diamond: All covalent bonds → Very hard, high m.p., doesn't conduct
Graphite: Layers held by weak forces → Soft, high m.p., conducts (mobile electrons)

Giant Covalent Properties

Melting point: VERY HIGH (strong covalent bonds throughout)
Conductivity: Usually none (except graphite)
Solubility: Insoluble in common solvents
Hardness: Very hard (except graphite)
State: Solids at room temperature

Metallic Bonding

Definition: Metal atoms lose valence electrons to form cations, with electrons delocalized in "electron sea".

Metal cations surrounded by mobile electrons
Electrons can move freely throughout structure
Metallic bond is the electrostatic attraction

Metallic Properties

Melting point: Medium to HIGH
Conductivity: EXCELLENT (delocalized electrons move freely)
Malleability: Can be bent/shaped (layers slide)
Ductility: Can be drawn into wires
Luster: Shiny (electrons absorb and reflect light)

Bonding Summary

Ionic: Electron transfer, high m.p., soluble in water

Covalent: Electron sharing, low m.p. (molecular), very high m.p. (giant)

Metallic: Delocalized electrons, conduct, malleable