Unit 1-5 Flashcards
(39 cards)
How are ionic crystals held together?
Strong electrostatic forces between oppositely charged ions
What is electric neutrality?
No overall charge
What is the coordination number?
The number of oppositely charged ions which surround an ion
Describe the structure of sodium chloride
Giant ionic lattice of Na+ cations and Cl- anions
Coordination number of 6:6
Each ion is surrounded by 6 of the oppositely charged ion
Na+ ions cant fit many Cl- ions around it due to a low number of shells
Describe the structure of caesium chloride
Giant ionic lattice made of Cs+ cations and Cl- anions
Coordination number of 8:8
Each ion is surrounded by 8 of the oppositely charged ion
Cs+ ions can fit many Cl- ions around it due to a large number of shells
What is metallic bonding?
The attraction between positive cations and a sea of negative delocalised electrons
The electrons move around both the ion they belong to and nearby ions
Why is the metal lattice built of cations?
Because while electrons don’t leave the structure they do leave the atom
Why does an increase in the number of electrons in the outer shell strengthen metallic bonding?
Cations increase in positivity
The number of delocalised electrons increases
Why do metals have high melting temperatures?
Strong attraction between the positive ions and sea of delocalised e-
Why are metals electrolytes
Electrons are free to move and carry electrical energy when potential difference is applied
Why are metals malleable and ductile?
Layers of metal ions can slide past each other since the sea of delocalised e- move to maintain metallic bonding
Why are metals hard and strong?
Strong metallic bonds require large amounts of energy to separate the cations and sea of delocalised e-
When covalent bonding extends indefinitely, what determines bonds per atom and direction of bonds?
Bonds per atom and direction of bonds are the same as that of the molecule
Unit 1.5
What is an allotrope?
Same element with a different arrangement of atoms within the structure
Diamond and graphite are allotropes of carbon
Unit 1.5
What is the structure of diamond?
Tetrahedral structure
Bond angle of 109.5°
Coordination number of 4
Unit 1.5
What is the structure of graphite?
Hexagonal arrangement
Bond angle of 120°
Coordination number of 3
Layers of carbon
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What holds the layers of graphite together?
Van-der-waals bonds
Weak bonds allow the layers to slide over eachother
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Describe the strength of diamond
Very hard due to strong covalent bonds creating a rigid structure
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Describe the strength of graphite
Soft due to weak VDW forces between layers
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Describe the conductivity of diamond
Does not conduct electricity as each carbon is bonded to 4 others, resulting in no free electrons
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Describe the conductivity of graphite
Does conduct electricity as each carbon is only bonded to 3 others, meaning there’s one free electron per atom of carbon
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Describe the melting point of diamond and graphite
Very high due to strong covalent bonds between carbon atoms
Graphites melting point is higher
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What is the density of diamond?
High density of 3.53g/cm3
C-C hold atoms closely per unit of volume
Unit 1.5
What is the density of graphite?
Low density of 2.25g/cm3
VDW bonds hold atoms far away
