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Chemistry > 1.3 Bonding Part 2 > Flashcards

1.3 Bonding Part 2 Flashcards

(76 cards)

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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
example of a molecule with hydrogen bonds
water
26
what is special about intermolecular forces
molecules with hydrogen bonds also contain permanent dipole-dipole forces and VDW forces molecules with permanent dipole-dipole forces also contain VDW forces
27
What are VDW forces caused by
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
28
What does the dipole constantly forming and disappearing induct
A dipole in neighbouring molecules, resulting in weak forces of attraction between molecules
29
VDW forces are present between all molecules but...
Not ions or metals
30
What properties do non-polar molecules have
Relatively low boiling points Generally gases/volatile liquids at room temperature
31
Why do bigger molecules have larger induced dipoles
They have more electrons
32
What do larger induced dipoles in bigger molecules result in
Stronger VDW forces between molecules
33
Where do permanent dipole-dipole forces occur
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
Where does hydrogen bonding occur
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
Why do substances which contain hydrogen bonds have higher boiling points than expected
Due to the strength of the hydrogen bonds (strongest intermolecular force)
36
Why do substances which contain hydrogen bonds dissolve in water
They form hydrogen bonds with water
37
Why does ice float on water
The density of ice is less than that of water.
38
Why does water expand when it solidifies (ice)
As the temperature gets to 0 degrees the water molecules are held further apart by hydrogen bonds in an open lattice
39
What is sublimation
When a material goes straight from a solid to a gas eg. Iodine and carbon dioxide
40
Energy is needed to change a substance from a solid to a gas to...
Overcome forces of attraction
41
When is a bond polar
When there is an uneven distribution of electrons
42
When is a bond polar
When there is an uneven distribution of electrons
43
When is a bond polar
When there is an uneven distribution of electrons
44
when can an electric current flow
if there are charged particles which are free to move ie. delocalised electrons or mobile ions
45
when can substances dissolve
if solute and solvent molecules attract one another
46
what can ionic and polar substances dissolve in
polar solvents such as water
47
what can non polar substances dissolve in
non polar solvents such as hexane
48
what is the structure in ionic compounds
giant ionic lattice
49
how are the ions arranged in the lattice
negative and positive ions alternate | . each ion surrounded by oppositely charged ions in all directions
50
in soldium chloride, what is each sodium ion surrounded by
6 chloride ions
51
in sodium chloride, what is each chloride ion surrounded by
6 sodium ions
52
what is the giant ionic lattice held together by
strong ionic bonds
53
why do ionic compounds have high melting points
lots of strong ionic bonds need to be broken
54
do ionic compounds conduct electricity
when solid no when dissolved/molten yes
55
why do ionic compounds not conduct electricity when solid
ions held fixed in the lattice
56
why can ionic compounds conduct electricity when molten/dissolved
ions free to move
57
why are ionic substances brittle
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
what is the structure of a metal
positive metal ions surrounded by a sea of delocalised electons positive ions fixed electrons free to move
59
why do metals have high melting points
giant structure and metallic bonds are strong
60
why can metals conduct electricity when solid/liquid
delocalised electons can flow through structure and carry the current
61
why are metals strong
metallic bonds are strong and extend through the giant metallic lattice
62
what does metallic bond strength depend on
size and charge of metal ion (smaller and higher charged ions are stronger)
63
what is a malleable substance
can be hammered or pressed into shape without breaking or cracking
64
what is a ductile substance able to do
be drawn into a wire
65
why are metals malleable/ductile
layers of ions in giant metallic lattice can slide over each other into new positions without disrupting metallic bond
66
what are the two main types of covalent substance
simple and giant/simple and macro-molecule
67
describe the structure of a molecular crystal of iodine
covalent bonds between iodine atoms- weak VDW forces between i2 molecules
68
why do simple covalent molecules have low melting points
all that Is needed is to overcome weak intermolecular forces (VDW,dipole-dipole, H-bonds)
69
are simple covalent molecules soluble
usually insoluble in water unless they can form hydrogen bonds/react with water
70
why don't simple covalent molecules conduct electricity
no charged partices which are free to move, don't contain ions/delocalised electrons
71
examples of macromolecular crystals
diamond, graphite and graphene
72
why do macromolecular crystals have a high melting point
strong covalent bonds between all atoms. Lots of energy needed to break these
73
why does diamond not conduct electricity
electrons are localised in the covalent bonds so are not free to move- no ions present
74
why does graphite conduct electricity
one electron per carbon not involved in bonding and is delocalised along the layer
75
why does graphene conduct electricity
better conductor than silver! delocalised electrons carry current
76
why are the macromolecular crystals insoluble in water
covalent bonds are very strong and the lattice does not break up when any solvent is added

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