Chemical Bonding: Ionic, Covalent, and Metallic Explained

Atomic Structure and Properties

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Outer Shells of Atoms

• 2 electrons
• 8 electrons
• 8 electrons

Key Definitions

• Isotopes: Atoms of a single element that have a different number of neutrons.
• Valency: The capacity of an atom to give, accept, or share electrons to achieve the octet state.

Ionic Bonding

Formation of Ions

Ions are formed when neutral atoms or molecules gain or lose electrons to achieve a stable, full outer shell. An ion is an atom that has lost or gained an electron.

• If an atom has lost an electron, it becomes a positive ion.
• If an atom has gained an electron, it becomes a negative ion.

Ionic Bonds

An ionic bond is the electrostatic attraction between a positively charged metal ion (cation) and a negatively charged non-metal ion (anion). Opposite charges attract.

Properties of Ionic Compounds

• High melting and boiling points
• Brittle
• Soluble in water
• Conduct electricity

Red = metal and blue = non-metal; Na+ = cation, Cl- = anion.

Covalent Bonding

How Covalent Bonds Form

Covalent bonding usually occurs between two non-metals. The outer shells overlap and they share electrons. The bond is a strong electrostatic attraction between the positive nucleus and the shared pair of negative electrons.

Properties of Covalent Substances

• Often have low melting and boiling points because the forces between molecules are weak.
• Do not contain ions or free electrons, so they do not conduct electricity.
• Intermolecular forces are stronger in molecules with higher molecular mass.

Metallic Bonding

Understanding Metallic Bonds

Metallic bonding consists of positively charged metal ions in a sea of delocalized (free) electrons. The metallic bond is the force of attraction between these free electrons and metal ions. The greater the charge of the metal ion, the greater the number of delocalized electrons and the stronger the bonds.

Properties of Metallic Compounds

• High melting and boiling points
• High density
• Malleable
• Good electrical and thermal conductors

Alloys

Alloys are mixtures of two or more elements where at least one is a metal. In an alloy, the atoms have different sizes, which distorts the layered structure. This means greater force is needed to make the layers slide over one another, which makes an alloy harder and stronger than a pure metal.

Cation and Anion

• Cation (Positive Ion): An atom or group of atoms that has a net positive charge. This occurs because the species has lost one or more electrons, resulting in more protons than electrons.
• Anion (Negative Ion): An atom or group of atoms that has a net negative charge. This occurs because the species has gained one or more electrons, resulting in more electrons than protons.