Simple & Giant Covalent Structures

Why are most simple molecular compounds liquids / gases?

Although the molecules have strong intramolecular covalent bonds, they are held together by weak intermolecular Van der Waals forces which require little energy to break.

What are the 2 examples of solid simple covalent structures?

• Iodine

• Ice

Describe the structure of iodine.

Iodine atoms are bonded in pairs by covalent bonds, so the formula is I₂.

Why is iodine a solid at room temperature?

• Iodine is in Group 7 among the halogens. There are Van der Waals forces among the halogen molecules, which are weak.

• Iodine has a large Mr (molecular mass), meaning that the strength of the Van der Waals forces is greater.

• More energy is required to break the strong intermolecular foces therefore, iodine is solid at room temperature.

What is sublimation?

The transition of a substance from the solid phase directly to the gaseous phase, without changing into the liquid phase.

Describe the structure of ice.

In ice, the hydrogen bonds hold the water molecules together in a hexagonal structure.

The hydrogen bonds in ice are fixed / permanent, creating an open structure. Therefore, ice will occupy a greater volume than the water it was formed from.

State some properties of simple covalent structures.

• Low melting and boiling points

• Poor conductors- no charged particles

• Usually liquids or gases

Give examples of giant covalent structures.

• Diamond

• Graphite

Diamond and graphite are allotropes of what element?

Carbon.

What is an allotrope?

Different structural forms of the same element in the same physical state.

Describe the structure of diamond.

In diamond, each carbon atom is covalently bonded to 4 other carbon atoms.

They are bonded tetrahedrally.

Describe the structure of graphite.

In diamond, each carbon atom is covalently bonded to 3 other carbon atoms in flat sheets.

The electrons not used in bonding are released as delocalised electrons which move between layers, meaning it can conduct electricity.

State the properties of giant covalent structures.

• Hardness- the strength of the covalent bonds make them rigid.

• Insoluble in water

• Conduct electricity- only graphite as it has delocalised electrons.

Giant covalent structures are also known as…

Macromolecular substances.