12 Chemistry Atomic Structure and Bonding CR 07 Types of solids Solids are classified according to their properties Properties of solids depend on: Particle type Bonding within and between the particles 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 Ionic Solids Ionic crystals are made of ions which sit in a 3D network of positive and negative ions. 12 Chemistry Atomic Structure and Bonding CR 07

Properties of Ionic solids Are very hard but can be cleaved 12 Chemistry Atomic Structure and Bonding CR 07

Ionic solids properties cont’d Do not conduct electricity (no free ions or electrons) except when molten or aqueous (as ions are free to move) High melting point and boiling point because of very strong inter-particular attractions (electrostatic attractions) 12 Chemistry Atomic Structure and Bonding CR 07

Ionic solids properties cont’d Soluble in polar substances Polar solvents overcome the electrostatic forces between ions 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 Molecular solids Molecular solids are made of molecules. There are strong bonds within the molecules (strong intra-molecular forces) but weak attractions between the molecules (weak inter – molecular forces) 12 Chemistry Atomic Structure and Bonding CR 07

Properties of molecular solids Have low melting and boiling points because of weak inter-molecular forces **The molecules themselves are not broken up – just moved apart from each other when molten 12 Chemistry Atomic Structure and Bonding CR 07

Molecular solids properties cont’d Do not conduct electricity - even when molten (no free ions or electrons) Insoluble in water and other polar substances Few are solid at room temperature – eg. Dry ice 12 Chemistry Atomic Structure and Bonding CR 07

Polar and non- polar particles Molecular solids can be made from polar or non polar molecules. The inter- molecular forces between non-polar molecules are only weak van der Waals forces. Van der Waals attractions are the weak electrostatic attractions between atoms of different EN 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 Polar molecules Polar molecules have dipoles and so have slightly stronger attractions between them meaning that the melting point of a polar molecular solid is a little higher because more energy is needed to overcome the slightly stronger forces. *be able to explain 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 Metallic solids Metals are made of positive nuclei held together by a sea of de- localised electrons (e- do not belong to any one nucleus) Forces between the particles are strong metallic bonds 12 Chemistry Atomic Structure and Bonding CR 07

Properties of metallic solids Malleable and ductile due to non-directional metallic bonds Good conductors of heat and electricity due to density and mobile electrons High melting and boiling points due to strong metallic bonds Not soluble 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 The strength of metallic bonds varies and so consequently the melting and boiling points of different metals varies. 12 Chemistry Atomic Structure and Bonding CR 07

Giant covalent network solids are made of atoms arranged in covalent networks with strong covalent bonds (very strong inter- particular bonds) between them 12 Chemistry Atomic Structure and Bonding CR 07

Types of network solids Linear chains 2-D layers 3-D covalent network 12 Chemistry Atomic Structure and Bonding CR 07

Types of network solids Linear chains are infinitely long linear chains held together by van der Waals Properties: Low MP but longer chains have higher MP than shorter ones Do no conduct electricity Soft and flexible Eg. Polythene, rubber, plastics 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 2. 2-D Layers held together by weak van der Waals forces. Graphite is made of layers of covalently bonded C atoms. The layers are held together by weak van der Waals forces and have delocalised electrons between them. *this is very unusual and graphite is the only non- metal to conduct electricity 12 Chemistry Atomic Structure and Bonding CR 07

Properties of Graphite Conducts electricity because of delocalised electrons High melting point – C atoms are held by strong covalent bonds Soft and greasy texture (used as a lubricant) as the layers slide past each-other easily – weak van der Waals forces. 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 Graphite structure 12 Chemistry Atomic Structure and Bonding CR 07

12 Chemistry Atomic Structure and Bonding CR 07 3. 3-D covalent network solids are made of atoms held together by strong covalent bonds. Diamond and silica (silicon dioxide) are two examples of covalent network solids. Diamond is the strongest substance known to man. 12 Chemistry Atomic Structure and Bonding CR 07

Properties of covalent network solids Covalent network solids have High MP (strong covalent bonds hold atoms in place) Do not conduct electricity (all electrons held in covalent bonds) Very hard/strong Insoluble in any solvent 12 Chemistry Atomic Structure and Bonding CR 07