1.5- Solid Structures Flashcards
(a)
Crystal structure of sodium chloride
Sodium chloride is a giant ionic crystal lattice made up of Na+ and Cl- ions held together with strong electrostatic attraction. The sodium ions are a lot smaller than the chloride ions.
(a)
NaCl coordination
number
6:6
(a)
Crystal structure of caesium chloride
Caesium chloride is a giant ionic crystal lattice made up of Cs+ and Cl- ions held together with strong electrostatic attraction. The structure is different to NaCl since the ions are of a similar size so ions of the same type don’t come into contact with one another.
(a)
CsCl coordination
number
8:8
(b)
Structure of diamond
In diamond, each carbon atom is joined to four others by strong covalent bonds. The atoms arrange themselves in a tetrahedral shape. This makes it very hard.
(b)
Properties of diamond- Melting temperature
It has a very high melting temperature because a lot of energy is needed to break the numerous strong covalent bonds.
(b)
Properties of diamond- Electricity
It does not conduct electricity as there are no free electrons or ions present.
(b)
Structure of graphite
Graphite consists of hexagonal layers. Each carbon is joined to three others by strong covalent bonds. The extra electrons are delocalised within the layer. The layers are held together by weak van der Waals forces.
(b)
Properties of graphite- Melting temperature
It has a very high melting temperature as it has strong covalent bonds in the hexagon layers.
(b)
Properties of graphite-
Texture
It is soft and slippery as the weak forces between the layers are easily broken, so the layers can slide over each other.
(b)
Properties of graphite- Electricity
It is a good conductor of electricity because the delocalised electrons are free to move along the layers so an electric current can flow.
(c)
Structure of iodine
In iodine, atoms are covalently
bonded in pairs to form diatomic I2
molecules. These molecules are held
together by weak van der Waals
forces and are arranged in a regular
pattern.
(c)
Structure of ice
In ice, molecules of water are
arranged in rings of six held together
by hydrogen bonds. In this ordered
structure, the water molecules are
further apart than they are in the
liquid state. Since there are large
areas of open space inside the rings,
ice is less dense than liquid water at
0˚C.
(d)
‘electron sea’ model for bonding in metals
Metals consist of a lattice of metal cations surrounded by a ‘sea’ of delocalised electrons. The strong metallic bond is due to the electrostatic forces of attraction between the nucleus of the cations and the delocalised electrons.
(e)
Ionic bonding
Ionic solids (crystals) are giant lattices of positive and negative ions. Structures are made of the same base unit repeated over and over again. The structure of the crystal depends on the relative number of ions and their sizes.
(e)
Physical properties of ionic bonding- Melting and boiling points
High melting and boiling temperatures
It takes a large amount of energy to overcome the strong electrostatic
forces between the oppositely charged ions.
(e)
Physical properties of ionic bonding- Solubility
Often soluble in water
The oxygen end of the water molecules is attracted to the positive ions, and the hydrogen ends of the water molecules are attracted to the negative ions.
(e)
Physical properties of ionic bonding- Strength
Hard but brittle
When force is applied, layers of ions slide over each other causing ions of the same charge to be next to each other; the ions repel each other and the crystal shatters.
(e)
Physical properties of ionic bonding- Electrical conductivity
Poor electrical conductivity when solid, but good when molten or dissolved
In the solid state, the ions are fixed in position by the strong ionic bonds; however, when molten or dissolved, the ions are free to move and will move to the electrode of opposite charge, so will carry the current.
(e)
Giant covalent structure
Giant covalent solids consist of networks of covalently bonded atoms
arranged into giant lattices.
(e)
Simple molecular
Consist of covalently bonded molecules held together by weak
intermolecular forces.
(e)
Physical properties of simple molecular- Melting and boiling points
Low melting and boiling temperatures
Although the covalent bonds within
the molecules are strong, the intermolecular forces holding the molecules together are weak and do not need much energy to break.
(e)
Physical properties of simple molecular- Electrical conductivity
Poor conductors of electricity
They do not contain delocalised electrons or ions.
(e)
Metal structure
Metal atoms bond together to form a giant metallic
structure.
(e)
Physical properties of metals
Good thermal conductors because the delocalised electrons can pass kinetic energy to each other.
Malleable and ductile
When a force is applied to a metal, the layers of cations can slide over each other; however, the delocalised electrons move with the cations and prevent forces of repulsion forming between the layers.
(e)
Physical properties of metals- Melting and boiling points
High melting temperatures
A large energy is needed to overcome the strong forces of attraction between the nuclei of the metal cations and the delocalised electrons; the melting temperature is affected by the number of delocalised electrons per cation and the size of the cation.
(e)
Physical properties of metals- Strength
Hard
The metallic bond is very strong.
(e)
Physical properties of metals- Electrical conductivity
Good conductors of electricity both in the solid and molten state
The delocalised electrons can carry a current because, when a potential difference is applied across the ends of a metal, they will be attracted to and move towards the positive terminal of the cell.
