Types of chemical bonds: distinguish ionic, covalent and metallic bonding in terms of electron transfer or sharing, and relate bond type to the elements involved.

What this topic is asking

The Core Curriculum asks you to distinguish the three types of chemical bond: ionic, covalent and metallic. You must describe each in terms of what the valence electrons do (transfer or share), explain that atoms bond to reach a more stable arrangement, and predict the bond type from the elements involved. This underpins the rest of the bonding module and the properties of substances.

Why atoms bond

This drive toward a full outer level explains the charges ions take and the number of bonds an atom forms. Sodium has one valence electron to lose; chlorine needs one to fill its outer level; together they reach stability by transferring that electron.

Ionic bonding

Sodium chloride is the standard example: sodium ($2\text{-}8\text{-}1$) loses one electron to become $\text{Na}^{+}$, and chlorine ($2\text{-}8\text{-}7$) gains it to become $\text{Cl}^{-}$. The resulting ions arrange into a regular lattice held together by attraction in all directions. Because metals have low ionization energies and nonmetals high electronegativities, the large difference favors electron transfer. Table S electronegativity values let you confirm a large difference, which signals an ionic bond.

Covalent bonding

Covalent bonding occurs between nonmetals because both atoms attract electrons strongly, so neither fully gives them up. In $\text{Cl}_2$ the two identical atoms share a pair equally (a nonpolar covalent bond); in $\text{HCl}$ the more electronegative chlorine pulls the shared pair toward itself (a polar covalent bond). Covalent bonding produces discrete molecules rather than an extended lattice, which gives molecular substances their distinctive low melting points.

Metallic bonding

This model, sometimes called the electron-sea model, is the Regents explanation for the characteristic properties of metals. It applies to a pure metal or an alloy, not to compounds.

Try this

Q1. State the type of bonding in magnesium oxide, $\text{MgO}$. [1 point]

• Cue. Ionic, because it forms between a metal (magnesium) and a nonmetal (oxygen) by electron transfer.

Q2. Explain why energy is released when a bond forms. [1 point]

• Cue. Bonded atoms are at a lower potential energy than separate atoms, and the difference is released as the bond forms.