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AS Level Chemistry > Unit 2 section 1 bonding and intermolecular forces. > Flashcards

Unit 2 section 1 bonding and intermolecular forces. Flashcards

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0
Q

Describe the shape of BeCl”2”.

A

Linear with angles of 180. It is flat and the chlorine atoms are on opposite sides of the beryllium.

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1
Q

What are the sidgewick Powell rules?

A

Electrons pairs repel.
A pair of electrons in a bond repel the least. Lone electron pairs repel the most.
Treat double bonds as if they were single bonds.

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2
Q

Describe the shape of BCl”3”

A

It is triganol and planar. The chlorines are at 120 to each other.

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3
Q

Describe the shape of methane.

A

It is CH”4”. There are no lone pairs. One hydrogen goes into the page and one out of it. The angle between any two covalent bonds is 109.5 degrees.

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4
Q

Describe the shape of an ammonia molecule.

A

There is one lone pair and 3 hydrogens bonded to a central nitrogen.
The lone pair is at 12 o’clock, a planar hydrogen at 4. One going out at 6 and one going in at 8.
The lone electron pair causes 2 hydrogens to move together meaning the angles between hydrogens are 107 degrees.
The molecule is the shape of a triangle based pyramid, with the nitrogen on top.

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5
Q

What is the shape of a water molecule?

A

There are 2 lone pair electrons (one going in and one going out)at 1 and 11 o’clock with two hydrogens at 5 and 7 o’clock. The angle between the two hydrogens is 104.5 degrees. The two are pushed together by the unpaired electrons.

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6
Q

What is the shape of the molecule when a carbon atom makes 4 double bonds?
What does this mean when you have single bonded carbon chains?

A

A tetrahedral shape. A triangle based pyramid with a carbon in the middle.
It will form a wiggly line if there are more than 3 carbons.
Carbons at an angle of 109.5

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7
Q

Describe the shape of a CO”2” molecule.

A

Planar and linear with the oxygens at 180 degrees from each other.

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8
Q

Describe the shape of an SO”2” atom.

A

The oxygen and sulphur form double bonds. There is an unpaired electron pair but and this repels the oxygens away. However the high charge densities of the double bonds also repel each other and this results in the angle between the oxygens being 120 degrees.

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9
Q

What does a wedge shape represent?

A

The atom is going out of the page.

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10
Q

What do several lines represent?

A

The atom is going into the page.

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11
Q

What is the shape of a molecule which has an atom with 5 pairs of bonded electrons in it?

A

The shape will be like 2 triangle based pyramids joined together at the base. The angles will be 120. One atom will go out and one will go in. These two will be next to each other.

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12
Q

What is the shape of a molecule with 6 bond pairs of electrons around a single atom?

A

It is the shape of 2 square bases pyramids joined together at the bottom. The atoms will be arranged planar, in, out, planar in, out.

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13
Q

Explain van der waals forces.

A

Temporary dipoles found between molecules. Electrons move around creating temporary areas of positive and negative charge which attract each other. One dipole in one molecule can induce a second one in a different molecule in the opposite direction meaning there are attracted.

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14
Q

What increases the size of van der waals forces?

A

The more electrons the greater the forces.
The larger the surface area. Long chains with no branching off have higher surface areas meaning a bigger exposed electron cloud.
The larger the molecule.

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15
Q

Which molecule has the smallest van der waals forces?

A

Helium.

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16
Q

Why does helium and not hydrogen have the smallest van der waals force?

A

Hydrogen forms H”2” which has the same number of electrons as helium but is larger. This creates a greater potential difference and a greater dipole.

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17
Q

What force will pull atoms together when they condense ?

A

Van der waals forces.

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18
Q

What are dipole dipole forces?

A

Like van der waals forces but permanent. Electronegative atoms in a molecule will pull electrons towards them creating a permanent positive and negative side.

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19
Q

What are the only molecules or parts of molecules that can create hydrogen bonds?

A

Hydrogen-nitrogen, hydrogen-oxygen and hydrogen-fluorine.
In each case the atom that isn’t hydrogen will have a free electron pair and will be slightly electronegative.
They are all covalent bonds.

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20
Q

Why does ammonia have a lower boiling point than water despite the fact that they both have the same number of electrons?

A

Water forms 2 hydrogen bonds while ammonia only forms 1 meaning there are stronger intermolecular forces to be overcome in water.

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21
Q

At what angle do hydrogen bonds form?

A
  1. They are straight lines.
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22
Q

How do hydrogen bonds work?

A

A hydrogen atom will be attached to a very electronegative atom it will slightly positive. It will have a large charge density as the hydrogen atom is small. The hydrogen will then form weak bonds will the lone pairs of electrons in the fluride, nitrogen and oxygen of other molecules.

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23
Q

What are the 3 types of intermolecular forces?

A

Instantaneous dipole-induced dipole forces.
Permanent dipole interactions
Hydrogen bonding.

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24
Q

Why do different alkanes have different boiling points?

A

The larger and longer the alkane the greater the van der walls forces.

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25
Q

What is the strongest of the 3 intermolecular forces?

A

Hydrogen bonds.

26
Q

How can hydrogen bonds affect the properties of materials?

A

Substances have greater boiling and melting points because of hydrogen bonds.

27
Q

Is the structure of ice and water affected by hydrogen bonds?

A

Ice contains more hydrogen bonds than liquid water and the bonds are fairly long. Thus the molecules in ice are further apart then in water meaning it is less dencse.

28
Q

What is an allotrope?

A

Different forms of the same element in the same state.

29
Q

What allotropes can carbon form?

A

Diamond, graphite and fullerenes.

30
Q

Explain the structure of diamond?

A

Each carbon atom is covalently bonded with sigma bonds to four more carbons. They have a tetrahedral shape.

31
Q

Explain the properties of diamond.

A

Very high melting point.
Very hard.
Vibrations travel through the structure well, meaning it is a good thermal conductor.
It can’t conduct electricity as all the outer shell electrons are held in localised bonds.
It won’t dissolve in any solvents.

32
Q

Explain the structure of graphite.

A

The carbons are arraigned in sheets of flat hexagons. Each forms 3 covalent bonds with 3 other atoms meaning the forth outer shell electron is delocalised.

33
Q

Describe and explain the properties of graphite.

A

The weak bonds between layers means graphite is easily broken so they can slide over each other so it can act as a dry lubricant.
The delocalised electrons aren’t attracted to a particular carbon atom and are free to move meaning it can conduct electricity.
The layers are quite far apart compared to length so it isn’t dense and can be used to make lightweight materials.
High boiling point.
Insoluble.

34
Q

What are fullerenes?

A

Molecules of carbon shaped like hollow balls or tubes. Each carbon atom forms 3 covalent bonds with its neighbours leaving free electrons that can conduct electricity. They are nano particles.

35
Q

What is a buckminsterfullerene ?

A

60 carbons bonded together to make a ball. They dissolve in organic solvents and can be used to cage other molecules which is useful in de living drugs in the body.

36
Q

Describe carbon nanotubes

A

The covalent bonds make it very strong.

They can conduct electricity.

37
Q

What are the bonds that can only be covalent?

A

Bonds between atoms of a single element like in diatomic gases.

38
Q

What is electro negativity?

A

The ability to attract the bonding electrons in a covalent bond.

39
Q

What is used to measure electronegativity?

A

The Pauling scale

40
Q

What are the first eight most electronegative elements?

A

Flurine, oxygen, nitrogen, chlorine, bromine, carbon, silicon, Iodine.

41
Q

Why are the bonds in diatomic gases polar?

A

No as both the atoms will have the same electronegativity, meaning the electrons are pulled with the same force in opposite direction meaning they don’t move.

42
Q

What is a dipole?

A

The difference in charge between the two atoms caused by a shift in electron density in the bond. If the difference is great enougth, the bond is effectively ionic.

43
Q

Why are stronger bonds shorter?

A

They pull the atoms closer together because of the strength.

44
Q

What must happen for solubility to occur?

A

Bonds in the substance have to break.
Bond in the solvent have to break.
New bonds have to form between the substance and the solvent.

45
Q

As a general rule, when will a substance dissolve?

A

The strength of the new bonds formed is about the same as or greater than the strength of the bonds broken.

46
Q

What are the two types of solvent?

A

Polar. Like water. They bond to each other with hydrogen bonds.
Non-polar solvents like hexane. They bond to each other with van der waals forces.

47
Q

How do ionic substances dissolve in water?

A

The ions are attracted to the oppositely charged ends of the water molecule. The ions are pulled away by the water molecules and surrounded by them.

48
Q

Why don’t some ionic compounds dissolve in polar solvents?

A

The bonding between the ions is too strong.
Aluminium oxide is insoluble in water because the bonds between the ions are stronger than the ones that would be formed with water.

49
Q

Why does alcohol dissolve in water?

A

They dissolve even though there are covalent.
The O-H bonds in the alcohol is attracted to the polar O-H bonds in the water. Hydrogen bonds form between the lone pairs on the negative oxygen and positive hydrogen. As the carbon chain of the alcohol is not solubale, it should be as small as possiable.

50
Q

Why don’t halogenalknes dissolve in water?

A

The dipoles aren’t strong enough to hydrogen bonds.

The hydrogen bonds between water molecules is stronger than the bonds that would be formed with halogenoalkanes.

51
Q

What do non-polar substances best dissolve in?

A

Non polar solvents.

52
Q

What are the possible disadvantages of nano particles in health things?

A

Prolonged exposure could be toxic or carcinogenic.

53
Q

What is the shape of a molecule with 2 bonding pairs and no lone pairs?

A

Linear. Bond angles = 180. E.g. CO₂, BeF₂

54
Q

What is the shape of a molecule with 3 bonding pairs and 0 lone pairs?

A

Trigonal planar. 120° e.g. BF₃, SO₃

55
Q

What is the shape of a molecule with 4 bonding pairs and 0 lone pairs?

A

Tetrahedral. One into the page, one out of it. 109.5˚. E.g. SiCl, SO₄²⁻

56
Q

What is the shape of a molecule with 3 bonding pairs and 1 lone pairs?

A

Trigonal pyramidal. 107° NCl₃, ClO₃

One in, one out.

57
Q

What is the shape of a molecule with 2 bonding pairs and 2 lone pairs?

A

Bent. Angles of 104.5° e.g. SCl₂, OF₂

58
Q

What is the shape of a molecule with 5 bonding pairs and 0 lone pairs?

A

Trigonal bi pyramidal. Angles of 120° and 90°. One in the page and one out. E.g. PCl₅

59
Q

What is the shape of a molecule with6 bonding pairs and 0 lone pairs?

A

Octahedral. 2 into the page, 2 out. Bond angles 90° e.g. SF₆

60
Q

What does a large or small electronegativity difference mean in a bond?

A

Large difference, a mainly ionic bond.

A small difference a mainly covalent bond.

61
Q

Where do van der waals forces not occur?

A

In ionic substances.

62
Q

What bond will commonly cause a permanent dipole?

A

C-Cl, C-Br, C-F, H-Cl, C=O

AS Level Chemistry (16 decks)

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