iGCSE Chemistry (Combined) OxfordAQA

Atomic Structure: Solids

Atomic Structure of Solids

Structural Basics

• Atoms in solids are packed closely together and have regular, repeating patterns.
• The atoms in most solids organise themselves in fixed patterns or lattice structures; this results in a defined shape or crystal structure.
• Solids are characterized by strong intermolecular forces that strongly attract and keep the atoms together.
• Due to these strong forces and the close proximity of the atoms, solids have a definite shape and are not easily compressible.

Atomic Bonds in Solids

• The atoms in solids are held together by strong bonds; these bonds are often covalent, ionic, or metallic.
• Covalent bonds involve atoms sharing their electrons.
• In ionic bonds, one atom transfers one or more electrons to another atom. This transfer creates positively and negatively charged ions that attract each other.
• Metallic bonds involve a sea of mobile or delocalised electrons, which allows metals to conduct electricity.

Types of Solids

• Covalently bonded solids, also called covalent network solids, have atoms bonded together by covalent bonds in a crystalline network. Examples include diamond and quartz.
• Ionic solids are formed of positive and negative ions arranged in regular patterns. These solids, such as sodium chloride (NaCl), are generally hard and brittle with high melting and boiling points.
• Metallic solids consist of a lattice of metal cations surrounded by a cloud of delocalised electrons, which gives them properties such as electrical conductivity and ductility.
• Molecular solids consist of atoms or molecules held together by weaker van der Waals forces or hydrogen bonds. Examples include oxygen (O2) and carbon dioxide (CO2) at low temperatures.rpar;

Heat and Energy in Solids

• In solids, the atoms vibrate about a mean position but do not have enough energy to overcome the intermolecular forces holding them in position.
• When heat is added to a solid, it increases the vibration of the atoms. If enough heat is added, the solid turns into a liquid (melting).