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Chemistry > 1.3 Bonding Part 2 > Flashcards

1.3 Bonding Part 2 Flashcards

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1
Q

Electronegativity

A

The power of an atom to attract the pair of electrons in a covalent bond

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2
Q

Top 5 electronegative elements

A

Fluorine, oxygen, nitrogen, chlorine and bromine

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3
Q

what is the trend in electronegativity across a period

A

increases

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4
Q

why does electronegativity increase across a period

A

nuclear attraction on outer electrons decreases

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5
Q

what is the trend in electronegativity down a group

A

decreases

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6
Q

why does electronegativity decrease down a group

A

nuclear attraction on outer electron decreases

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7
Q

do noble gases have electronegativity values?

A

no because they don’t normally form covalent bonds

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8
Q

what is electronegativity like in a non polar bond

A

same atom so same electronegativity

electrons are evenly distributed

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9
Q

what is electronegativity like in a polar covalent bond

A

significant difference in electronegativity

covalent bond where electrons are unevenly distributed

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10
Q

what is electronegativity like in an ionic bond

A

difference so large that electrons permanently go to one of atoms forming ions

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11
Q

what does delta mean

A

difference

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12
Q

how do we show a negative charge on an atom involved in a polar bond

A

delta negative

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13
Q

how do we show a positive charge on an atom involved in a polar bond

A

delta positive

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14
Q

what do charges depend on

A

how electronegative the atom is- more electronegative- more power to attract electrons- negative

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15
Q

what are hydrocarbons non-polar

A

carbon and hydrogen have similar electronegativity

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16
Q

what do polar bonds mean in a simple molecule

A

the whole molecule has an uneven distribution of electrons

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17
Q

what happens in more complex molecules

A

the dipoles of the polar bonds may cancel out

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18
Q

what decides whether dipoles cancel out or not

A

whether the molecule is symmetrical or not

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19
Q

what are intermolecular forces

A

forces of attraction between molecules

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20
Q

what are the three types of intermolecular force

A
  • van der Waals’ force
  • permanent dipole-dipole forces
  • hydrogen bonds
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21
Q

which substances have van der Waals’ forces within them

A

all molecules and atoms

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22
Q

which molecules contain permanent dipole-dipole forces (and VDW)

A

between polar molecules

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23
Q

what is a hydrogen bond

A

special case of permanent dipole-dipole force

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24
Q

where do hydrogen bonds occur (and VDW and permanent dipole-dipole)

A

where theres a delta plus hydrogen atom and either a nitrogen, oxygen, fluorine with a lone pair

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25
Q

example of a molecule with hydrogen bonds

A

water

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26
Q

what is special about intermolecular forces

A

molecules with hydrogen bonds also contain permanent dipole-dipole forces and VDW forces

molecules with permanent dipole-dipole forces also contain VDW forces

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27
Q

What are VDW forces caused by

A

The movement of electrons which unbalances the charge distribution within the molecule. This creates an instantaneous dipole across the molecule

The instantaneous dipole is constantly forming and disappearing

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28
Q

What does the dipole constantly forming and disappearing induct

A

A dipole in neighbouring molecules, resulting in weak forces of attraction between molecules

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29
Q

VDW forces are present between all molecules but…

A

Not ions or metals

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30
Q

What properties do non-polar molecules have

A

Relatively low boiling points

Generally gases/volatile liquids at room temperature

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31
Q

Why do bigger molecules have larger induced dipoles

A

They have more electrons

32
Q

What do larger induced dipoles in bigger molecules result in

A

Stronger VDW forces between molecules

33
Q

Where do permanent dipole-dipole forces occur

A

Between molecules which have a permanent dipole

They occur in addition to VDW forces

The delta positive end of one molecule is attracted to the delta negative end of a neighbouring molecules

Stronger than VDW forces

34
Q

Where does hydrogen bonding occur

A

Between molecules which contain a hydrogen atom bonded to either F, O or N

Between a delta positive hydrogen atom in one molecule and a lone pair of electrons in an N, O or F in a neighbouring molecule

Occur in addition to VDW

Strongest intermolecular force

35
Q

Why do substances which contain hydrogen bonds have higher boiling points than expected

A

Due to the strength of the hydrogen bonds (strongest intermolecular force)

36
Q

Why do substances which contain hydrogen bonds dissolve in water

A

They form hydrogen bonds with water

37
Q

Why does ice float on water

A

The density of ice is less than that of water.

38
Q

Why does water expand when it solidifies (ice)

A

As the temperature gets to 0 degrees the water molecules are held further apart by hydrogen bonds in an open lattice

39
Q

What is sublimation

A

When a material goes straight from a solid to a gas eg. Iodine and carbon dioxide

40
Q

Energy is needed to change a substance from a solid to a gas to…

A

Overcome forces of attraction

41
Q

When is a bond polar

A

When there is an uneven distribution of electrons

42
Q

When is a bond polar

A

When there is an uneven distribution of electrons

43
Q

When is a bond polar

A

When there is an uneven distribution of electrons

44
Q

when can an electric current flow

A

if there are charged particles which are free to move ie. delocalised electrons or mobile ions

45
Q

when can substances dissolve

A

if solute and solvent molecules attract one another

46
Q

what can ionic and polar substances dissolve in

A

polar solvents such as water

47
Q

what can non polar substances dissolve in

A

non polar solvents such as hexane

48
Q

what is the structure in ionic compounds

A

giant ionic lattice

49
Q

how are the ions arranged in the lattice

A

negative and positive ions alternate

. each ion surrounded by oppositely charged ions in all directions

50
Q

in soldium chloride, what is each sodium ion surrounded by

A

6 chloride ions

51
Q

in sodium chloride, what is each chloride ion surrounded by

A

6 sodium ions

52
Q

what is the giant ionic lattice held together by

A

strong ionic bonds

53
Q

why do ionic compounds have high melting points

A

lots of strong ionic bonds need to be broken

54
Q

do ionic compounds conduct electricity

A

when solid no

when dissolved/molten yes

55
Q

why do ionic compounds not conduct electricity when solid

A

ions held fixed in the lattice

56
Q

why can ionic compounds conduct electricity when molten/dissolved

A

ions free to move

57
Q

why are ionic substances brittle

A

if enough force is applied the layers slide over eachother because like charges move next to eachother, causing repulsion and the lattice structure breaks down

58
Q

what is the structure of a metal

A

positive metal ions surrounded by a sea of delocalised electons

positive ions fixed

electrons free to move

59
Q

why do metals have high melting points

A

giant structure and metallic bonds are strong

60
Q

why can metals conduct electricity when solid/liquid

A

delocalised electons can flow through structure and carry the current

61
Q

why are metals strong

A

metallic bonds are strong and extend through the giant metallic lattice

62
Q

what does metallic bond strength depend on

A

size and charge of metal ion (smaller and higher charged ions are stronger)

63
Q

what is a malleable substance

A

can be hammered or pressed into shape without breaking or cracking

64
Q

what is a ductile substance able to do

A

be drawn into a wire

65
Q

why are metals malleable/ductile

A

layers of ions in giant metallic lattice can slide over each other into new positions without disrupting metallic bond

66
Q

what are the two main types of covalent substance

A

simple and giant/simple and macro-molecule

67
Q

describe the structure of a molecular crystal of iodine

A

covalent bonds between iodine atoms- weak VDW forces between i2 molecules

68
Q

why do simple covalent molecules have low melting points

A

all that Is needed is to overcome weak intermolecular forces (VDW,dipole-dipole, H-bonds)

69
Q

are simple covalent molecules soluble

A

usually insoluble in water unless they can form hydrogen bonds/react with water

70
Q

why don’t simple covalent molecules conduct electricity

A

no charged partices which are free to move, don’t contain ions/delocalised electrons

71
Q

examples of macromolecular crystals

A

diamond, graphite and graphene

72
Q

why do macromolecular crystals have a high melting point

A

strong covalent bonds between all atoms. Lots of energy needed to break these

73
Q

why does diamond not conduct electricity

A

electrons are localised in the covalent bonds so are not free to move- no ions present

74
Q

why does graphite conduct electricity

A

one electron per carbon not involved in bonding and is delocalised along the layer

75
Q

why does graphene conduct electricity

A

better conductor than silver! delocalised electrons carry current

76
Q

why are the macromolecular crystals insoluble in water

A

covalent bonds are very strong and the lattice does not break up when any solvent is added

Chemistry (42 decks)

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