Unit 1-5 Flashcards
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
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What is an allotrope?
Same element with a different arrangement of atoms within the structure
Diamond and graphite are allotropes of carbon
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What is the structure of diamond?
Tetrahedral structure
Bond angle of 109.5°
Coordination number of 4
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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
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What is the density of graphite?
Low density of 2.25g/cm3
VDW bonds hold atoms far away
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Describe the solubility of diamond and graphite
Insoluble
Covalent bonds are so strong the atoms cannot be separated by the solvent
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What is the range of sizes for nanoparticles?
1-100 nanometers (nm)
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What are fullerenes?
Nanoparticles of carbon shaped as hollow spheres or closed tubes
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Why do fullerenes have a high melting point?
Strong covalent bonds
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Why are fullerenes conductive?
1 free electron per carbon atom
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What is a buckminster?
The smallest fullerene (C60)
Shaped as a hollow sphere
Used as cages to administer drugs into the body
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What are carbon nanotubes?
Cylindrical fullerenes consisting of hexagons of carbon
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What are the properties of carbon nanotubes?
Very high tensile strength
Unique electrical properties
Good heat conductance
Large surface area
Metal atoms can be attached to the outside
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What are the uses of carbon nanotubes
Used for semiconductors in electronic circuits
Often used to reinforce various objects, such as tennis racket frames and golf club shafts
Used as a platform for industrial catalysts due to large surface area
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What are multiwalled nanotubes?
Several tubes rotate and slide within each other with almost no friction
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What are D-molecular crystals?
Discrete molecules bonded by strong intermolecular VDW bonds
Stronger intramolecular covalent bonds between atoms
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Why do I2 crystals have a higher melting point than Cl2 crystals?
The strength of VDW forces increase with molecular size
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What are the general properties of D-molecular crystals?
Soft
Low melting and boiling point
Do not conduct electricity as solid or liquid (don’t exist as gases)
Soluble in polar solvelnts (H2O)
Insoluble in non-polar solvents (tetrachloromethane)
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Why are D-molecular crystals insoluble in polar solvents?
VDW forces are not strong enough to break the up the H-bonding between polar molecules
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What is the structure of ice?
Liquid H2O is tetrahedral and has H bonds bustween neighbouring O and H atoms
