Electrons, bonding and structure 2

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What are giant covalent lattices?
Huge networks of covalently bonded atoms, formed due to carbon's valence of 4.
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What are the properties of diamond and why?
high melting point due to many covalent bonds. Hardness due to 4 bonds (tetrahedral shape =external forces are spread throughout the structure.) Can't conduct electricity as all electrons are used in covalent bonds. Insoluble due to strong bonds.
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What are the properties of simple molecular structures and why?
Strong covalent bonds within molecules but weak Van der Waal's forces so less energy needed to overcome forces and lower boiling point. Not a conductor as there are no free electrons. Soluble in non-polar solvents (VDW between structure and solvent
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What is the structure of graphite?
Carbon atoms arranged in hexagonal layers since the fourth outer electron is delocalised between the layers. The layers are bonded together by weak Van der Waal's forces.
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What are the properties of graphite and why?
Graphite soft and slippery- weak VDW forces between layers easily broken so sheets can slide. Conductor of electricity- delocalised electrons. High melting point and insoluble- covalent bonds. Layers far apart- less dense.
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What is metallic bonding?
The attraction of cations to delocalised electrons.
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What does delocalised mean?
The electrons are shared between all the ions in the metallic structure.
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What are the properties of metals and why?
Malleable and ductile- electrons delocalised cations can slide over eachother.electrical conductor- delocalised electrons can move carrying a current. Insoluble due to the strength of metallic bonding. Higher charge of cations=higher MB point
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Describe the Valence shell electron pair repulsion theory
Electrons are all negatively charged so repel each other as much as possible. Lone pairs repel more than bonding pairs. Lone pair/lone pair bond angles are the biggest.
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Give the name of the shape, angles and examples of molecules forimg when there are 2 electron densities on the central atom.
Linear molecules. 180. carbon dioxide.
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Give the name, angles and examples of molecules forimg when there are 3 electron densities on the central atom.
Trigonal planar. 120. Boron trifluoride.
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Give the name, angles and examples of molecules forimg when there are 4 electron densities on the central atom and 4 bond pairs.
Tetrahedral. 109.5. Ammonium ion.
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Give the name, angles and examples of molecules forimg when there are 4 electron densities on the central atom and 1 lone pair.
Trigonal pyramidal. 107. Ammonia.
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Give the name, angles and examples of molecules forimg when there are 4 electron densities on the central atom and 2 lone pairs.
non linear. 104.5. water.
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Give the name, angles and examples of molecules forimg when there are 6 electron densities on the central atom with 6 bond pairs.
octahedral. 90. sulfur hexafluoride.
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What is electronegativity?
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.
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How do covalent bonds become polarised?
By differences in electronegativity in an atom.
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What is a dipole?
A small charge difference across a bond, pulling the bonding pair towards the more electronegative atom (shift in electron density), polarising the atom.
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What happens in symmetrical molcules?
dipoles of any bonds cancel out.
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What happens due to partial charges in polar molecules?
There are weak electrostatic charges due to opposite charges attracting (permanent dipole- dipole interactions.)
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What is hydrogen bonding?
A strong dipole-dipole attraction between an electron deficient H atom on one molecule and a lone pair of electrons on a highly electronegative atom.
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Which elements are involved?
Hydrogen- fluorine, nitrogen or oxygen.
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What is the effect of hydrogen bonding on the properties of water?
Hydrogen bonds are the strongest intermolecular force needing to be overcome by higher boiling points than atoms of a similar molecular mass. Ice has an open lattice structure with hydrogen bonds holding water molecules apart so it is less dense.
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How are temporary dipoles formed?
Electrons are always moving and can be closer to either atom in a bond at any time. This causes an instantaneous dipole which induces another dipole on a neighbouring molecule. These dipoles are created and destroyed all the time.
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How do electrons affect boiling point?
More electrons = stronger VDW which need more energy to overcome = higher boiling point.
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Card 2

Front

What are the properties of diamond and why?

Back

high melting point due to many covalent bonds. Hardness due to 4 bonds (tetrahedral shape =external forces are spread throughout the structure.) Can't conduct electricity as all electrons are used in covalent bonds. Insoluble due to strong bonds.

Card 3

Front

What are the properties of simple molecular structures and why?

Back

Preview of the front of card 3

Card 4

Front

What is the structure of graphite?

Back

Preview of the front of card 4

Card 5

Front

What are the properties of graphite and why?

Back

Preview of the front of card 5
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