1.5 Solid structures Flashcards
Describe the crystal structure of sodium chloride
sodium chloride has a giant ionic crystal lattice made up of Na⁺ and Cl⁻ ions and is held together by strong electrostatic attraction.
This is a face centred cubic lattice as the ions are arranged in a cube with an ion at each corner and at the centre of each face.
Describe the crystal structure of caesium chloride
Caesium chloride has a giant ionic crystal lattice made up of Cs⁺ and Cl⁻ ions and is held together by strong electrostatic attraction.
It has a body centred cubic structure and the central ion is wholly inside the unit cell.
Define coordination number
The number of nearest oppositely charged neighbours within the structure
What is the coordination number of sodium chloride and why?
6,6
because each cation is surrounded by 6 anions and each anion is surrounded by 6 cations
What is the coordination number of caesium chloride and why?
8,8
because each cation is surrounded by 8 anions and each anion is surrounded by 8 cations
Name two giant covalent structures formed by carbon ions
Diamond and graphite
Describe the structure of graphite
Giant covalent structure
each atom is bonded to three other carbon atoms
carbon atoms form layers of hexagonal rings
Weak intermolecular forces between layers however strong covalent bonds between the carbon atoms
One delocalised electron per carbon atom
Why is graphite soft?
Because there are weak intermolecular forces hold the layers therefore allows the layers to slide over each other. One use of graphite is lubricant,
Why can graphite conduct electricity?
Because each carbon atom is bonded to three other carbon atom, therefore leaving one delocalised electron which carry charge. One use of graphite is arc lamp electrodes.
Describe the structure of diamond
Giant covalent structure in which each carbon atom is bonded to 4 other carbon atoms and is arranged in a tetrahedral structure.
Strong covalent bonds between carbon atoms
No delocalised electrons or charges.
Describe the properties of diamond
Very hard
High melting points
Doesn’t conduct electricity
Why is diamond very hard?
Because each carbon atom is bonded with 4 other carbon atoms, forming strong covalent bonds between them in a tetrahedral structure.
Why does diamond has a high melting point?
Because there are strong covalent bonds in all directions therefore needs a large amount of energy to break them.
Why can’t diamond conduct electricity?
Because each carbon atom is bonded with 4 other carbon atoms therefore no delocalised electrons are avaliable to carry charges.
