Question

State the type of bonding -ionic, covalent, or metallicyou would expect in each: (a) \(\operatorname{Cr}(s)\) (b) \(\mathrm{H}_{2} \mathrm{~S}(g)\) (c) \(\mathrm{CaO}(s)\)

Short answer

(a) metallic, (b) covalent, (c) ionic

Step-by-step solution

Identify the first substance

Look at the chemical formula \(\text{Cr}(s)\). Chromium is a metal, so the bonding type expected is metallic bonding.

Identify the second substance

Consider the chemical formula \(\text{H}_2 \text{S}(g)\). Hydrogen and sulfur are both non-metals. Non-metals typically form covalent bonds with each other.

Identify the third substance

Examine the chemical formula \(\text{CaO}(s)\). Calcium is a metal and oxygen is a non-metal. Metals and non-metals usually form ionic bonds.

Key concepts

metallic bonding

In metallic bonding, atoms of metal elements come together, and their outer electrons are shared freely among a lattice of metal cations. This free movement of electrons, known as a 'sea of electrons,' allows metals to conduct electricity and heat efficiently. For example, in \(\text{Cr}(s)\), or solid chromium, this type of bonding is present. Metallic bonding gives metals their characteristic properties:

• High electrical and thermal conductivity
• Malleability and ductility, allowing them to be shaped and drawn into wires
• Shiny appearance due to the delocalized electrons reflecting light

So, when you see a metal element like chromium, you can expect metallic bonding.

covalent bonding

Covalent bonding occurs when two non-metal atoms share electron pairs, allowing each atom to achieve a stable electron configuration. This kind of bond is typically strong and directional. For example, in \(\text{H}_2 \text{S}(g)\), or hydrogen sulfide gas, hydrogen and sulfur, both non-metals, form covalent bonds by sharing electrons. Here are some properties of covalent compounds:

• Low melting and boiling points compared to ionic compounds
• Poor electrical conductivity in both solid and liquid states
• Can form simple molecules like \(\text{H}_2 \text{S}\) or giant covalent structures like diamonds

When you encounter compounds formed by non-metals, covalent bonding is usually responsible for their formation and properties.

ionic bonding

Ionic bonding happens when a metal atom transfers one or more electrons to a non-metal atom, resulting in the formation of positively charged cations (metal ions) and negatively charged anions (non-metal ions). This transfer helps both atoms achieve a more stable electronic arrangement. For example, in \(\text{CaO}(s)\), or solid calcium oxide, calcium (which is a metal) gives up electrons to oxygen (a non-metal), forming \(\text{Ca}^{2+}\) and \(\text{O}^{2-}\). Key characteristics of ionic compounds include:

• High melting and boiling points due to strong electrostatic forces between ions
• Good electrical conductivity in molten or aqueous states, but not as solids
• Often form crystalline structures, making them hard and brittle

When you see a metal and a non-metal forming a compound, ionic bonding is likely the force holding them together.