1.5 Flashcards
Crystal co-ordination number of Caesium chloride
8:8
Crystal co-ordination number of Sodium chloride
6:6
Why is CsCl co-ordination number bigger than NaCl
Cs+ is a larger ion so it can accommodate more Cl anions
How are ionic crystal structures arranged
Ions are arranged so that the electrostatic attraction between oppositely charged ions is greater than electrostatic repulsion between ions of the same charge
Describe the shape of sodium chloride
Cubic lattice
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Caesium chloride shape
Lattice made up of 2 interpenetrating simple cubic structures
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Which ion to show as smaller in diagrams of ionic crystal structures
The cation
Physical properties of ionic crystal structures
- high melting temperature
- soluble in water
- hard but brittle
- conducts electricity when liquid but not solid
High melting temperature of NaCl
Giant lattices held by strong electrostatic forces between oppositely charged ions which require a lot of energy to overcome
Solubility in water of NaCl
As water molecules are polar when in solution the O&- attracted to the cations and the H&+ to the anions
The water molecules pull the ions away form the lattice and the solid dissolves
Hard but brittle property of NaCl
When force is applied the layers of ions slide over each other which causes the ions of the same charge to be next to each other which causes the ions to repel each other and the crystal shatters
Describe electrical conductivity of NaCl
Solid - poor as the ions are fixed in position by ionic bonds
Liquid - good are the ions are no longer in a lattice and so can move freely and carry a flow of charge = electrical current
Describe the structure and bonding in diamond
• tetrahedral structure due to each C atom covalently bonded to 4 others
Diamond properties
- high melting temperature
- doesn’t conduct electricity
- very hard
- insoluble in water
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Why does diamond have a very high melting temperature
Strong covalent bonds between atoms
Why doesn’t diamond conduct electricity
No free electrons to carry an electrical current
Why is diamond so hard
Strong C-C bonds and due to its geometrical rigidity
Why is diamond insoluble in water
No ions present to be attracted by polar water molecules
Describe structure and bonding in graphite
- layers of hexagonal rings held by van der waals forces
- within the layers each C is covalently bonded to 3 others
- 4th electron from each C atom is delocalised within the layer
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Properties of graphite
- high melting temperature
- good electricity conductor
- insoluble in water
- soft, slippery feel
- low density
Why does graphite have a high melting temperature
There are strong covalent bonds in hexagonal layers
Why is graphite a good electricity conductor
Delocalised electron is free to move along the layers so an electrical current can flow
Only conducts parallel to it’s lines as the electron isn’t free to move from one layer to the next
Why is graphite insoluble in water
No ions to attract polar water molecules
Why does graphite have a soft, slippery feel?
The Van der waals forces between layers are easily broken so the layers can slide over each other
May be used as lubricant
Why does graphite have a low density
There is a lot of space between layers as the length of the van der waals are longer than the covalent bonded
May be used as strong, lightweight sport equipment
Structure of iodine
Crystal lattice
Covalent bonds within molecules held together by van der waals forces
Properties of iodine
- low melting temperature
- poor electrical conductors
- normally insoluble in water
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Why does Iodine have a low melting temperature
Weak van der waals forces between molecules which don’t need much energy to break
Why is Iodine a poor electrical conductor
Doesn’t contain charged particles
Why are molecules such as iodine normally insoluble in water
No ions to attract the polar water molecules
Describe the structure of ice
- water molecules are arranged in rings of 6 held by hydrogen bonds
- each water molecule is hydrogen bonded to 4 others in a tetrahedral coordinated lattice structure
- water molecules spread out and it has an open structure and so a lower density than water
Properties of ice
- unusually high boiling point
* poor conductors of electricity
Why does ice have an unusually high boiling point
Due to presence of hydrogen bonds
Why is ice a poor conductor of electricity
Doesn’t contain delocalised electrons or ions
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Describe the structure and bonding of metals
- giant metallic structure
- regular arrangement of metal cations (lattice) which is surrounded by a sea of delocalised electrons
- strong metallic bond due to electrostatic forces of attraction between nucleus of cations and delocalised electrons
- increasing temperature with increased number of delocalised electrons as the attraction is higher - more electrons and stronger cation
Properties of metals
- high melting temperature
- hard
- good thermal conductor
- good electrical conductors
- malleable and ductile
Why do metals have high melting temperatures
Strong forces of attraction
Why are metals hard
Strong metallic bonds
Why are metals good thermal conductors
Delocalised electrons can pass kinetic energy to each other
How are metals good conductors of electricity
Delocalised electrons carry current as when a potential difference is applied across end of a metal
Electrons will be attracted and move towards the positive terminal of the cell
Why are metals malleable and ductile
When force is applied the layers of cations can slide over each other but as the delocalised electrons move with the cations it prevents the forces of repulsion forming between layers
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