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Aqa a level chemistry > Topic 3: Bonding (physical chemistry) > Flashcards

Topic 3: Bonding (physical chemistry) Flashcards

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1
Q

what is metallic bonding defined as

A

electrosatic force of attraction between cations and delocalised electrons in a lattice structure

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2
Q

describe covalent bonding

A

shared pair of electrons between non metals. Attraction between nucleus and electrons

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3
Q

describe metallic bonding

A

giant lattice. Positive cations with a sea of delocalized electrons

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4
Q

describe ionic bonding

A

Giant lattice. Metal and non metal. Donation and loss of electrons. Electrostatic attraction between oppositely charged ions

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5
Q

what is the bonding like for noble gases (group 8)

A

no bonding (stable full outer shell)

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6
Q

what are some similarities between ionic and metallic bonding

A

-Both have cations

-Giant lattices

-Both have strong electrosatic forces of attraction between opposite charges

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7
Q

ionic bonding

A

Ionic bonding:

-Non metal anion and metal cation

-Dot and cross diagrams are used to depict this

Formation of ions:

-A sodium ion would loose one electron to form a cation with a singly positive charge

-A chlorine atom would have to gain an electron to form an anion with a singly negative charge

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8
Q

state one observation when magnesium reacts with steam

A

white powder forms
Mg (s) + H2O (g) –> MgO (s) + H2

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9
Q

describe the bonding in magnesium

A

attraction between the lattice of Mg2+ ions and delocalised electrons

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10
Q

Explain why magnesium chloride has a high melting point

A

-giant ionic lattice
-strong electrostatic forces of attraction
-between Mg2+ and Cl- ions

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11
Q

give one medical use for MgOH2

A

indigestion relief

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12
Q

what does a single covalent bond contain

A

a shared pair of electrons

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13
Q

how many electrons are shared in a single, double and triple covalent bond

A

single - 2
double - 4
triple -6

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14
Q

what does a dative bond contain

A

a shared pair of electrons with both electrons supplied by one atom

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15
Q

define metallic bonding

A

Metallic bonding involves attraction between delocalised electrons and positive ions arranged in a lattice.

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16
Q

what is an ionic bond

A

the electrostatic force of attraction between oppositely charged ions

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17
Q

what is the structure of an ionic compound

A

giant lattice of metal cation and non metal anions held together by strong electrostatic forces of attraction between oppositely charged ions

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18
Q

what does it mean if ionic bonding is strong

A

which means that a large amount of energy is required to overcome the electrostatic force of attraction between oppositely charged ions

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19
Q

what does it mean if a lot of ions are present in an ionic lattice

A

each ion is attracted to many oppositely charged ions so a large amount of energy is required to overcome the electrostatic force of attraction

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20
Q

what is bond strength dependent on

A

-Radii is the size of the ion (radius) –> distance between the nucleus and the outer electron

-High charges and small radii have the strongest force of attraction

-The greatest attraction and strongest ionic bond forms small highly charged ions –> nuclear charge, atomic radius, shielding, attraction

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21
Q

how are dative covalent bonds indicated

A

using an arrow from the lone electron pair

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22
Q

how are covalent bonds held together

A

weak van der waals forces

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23
Q

true or false simple covalent molecules are poor conductors

A

true –> structure contains no charged particles

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24
Q

Explain how the ions are held together in a solid sodium metal

A

electrostatic forces of attraction between positive lattice and delocalised electrons

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25
Q

explain how the ions are held together in solid sodium chloride

A

strong electrostatic forces of attraction between oppositely charged ions

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26
Q

Why can metallic compounds conduct electricity

A

delocalised electrons flow through the structure and carry charge

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27
Q

why is sodium metal malleable

A

layers in lattice can slide over eachother

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28
Q

what statement about inorganic ionic compounds is always correct

A

they form giant structures

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29
Q

which molecule is not able to form a co-ordinate bond with another species

A

NH3 (permanent dipole)

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30
Q

Explain why flouride ion is larger than a sodium ion

A

flouride ion has lower nuclear charge so weaker attraction between nucleus and outer electron

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31
Q

Name the type of bond formed when HF reacts with H+

A

Dative covalent bond –> lone pair of electrons is donated from flourine

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32
Q

true or false - graphite has delocalised electrons

A

true

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33
Q

name the strongest attractive force between two ammonia molecules

A

hydrogen bonds

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34
Q

define electronegativity

A

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

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35
Q

Do group 1 or group 2 ions has stronger bonding

A

Group 2
-high nuclear charge

-smaller ionic radius

-stronger electrostatic forces of attraction

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36
Q

what ion is larger Na+ or Li+

A

Na+ –> more shielding

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37
Q

What ion has a larger radius K+ or Ca2+

A

-K+ has a larger radius than Ca2+ due to weaker nuclear charge

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38
Q

what happens as ionic radius decreases

A

attraction increases

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39
Q

why do ionic compounds have a high melting and boiling point

A

-high nuclear charge

-smaller ionic radius

-stronger electrostatic forces of attraction

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40
Q

why are ionic compounds brittle

A

-As force is applied the structure will move so that like ions are next to eachother. This results in repulsion of the ions

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41
Q

Suggest why MgO has a higher boiling point than NaCl

A

-Mg2+ has a greater nuclear charge than Na+

-MgO has a smaller ionic radius

-Therefore stronger electrostatic forces of attraction between Mg2+ and O2-

-This means that more energy is required to overcome forces of attraction

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42
Q

can ionic compounds conduct electricity

A

-Only conduct when molten or aqueous as ions become free to move when a potential difference is applied

-cannot conduct when solid as ions are in a fixed lattice so cannot move freely

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43
Q

define covalent bonding

A

the sharing of a pair of electrons between two non-metal atoms. There is a force of attraction present between the nuclei and both atoms of the electron pair

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44
Q

H—-H –> what does this line represent?

A

the line represents the covalent bond which is the shared pair of electrons

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45
Q

what do dot and cross diagrams show

A

the bonding pairs of electrons in a compound, we can use these to represent ionic and covalent bonding

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46
Q

what is the success criteria for dot and cross diagrams

A

-outer shell electrons

-how many electrons are required

-draw bonding pair

-draw lone pairs

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47
Q

what do lone pair of electrons do

A

Lone pairs of electrons:

–> They affect the shape of molecules

–> are important in chemical reactions of some compounds

–> are used to form dative covalent bonds

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48
Q

the melting point of sodium chloride is much higher than that of sodium metal. why?

A

ionic bonding is stronger than metallic bonding. this means that a lot of electron is required to overcome strong electrostatic forces of attraction

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49
Q

explain why the boiling point of water is much higher than the boiling point of hydrogen sulfide

A

-hydrogen bonding is stronger than intermolecular forces of attraction

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50
Q

what are the features of sodium chloride

A

-ionic crystal structure
-high melting and boiling points
-brittle

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51
Q

structure/features of diamond

A

-tetrahedral substance
-4 carbon bonds
-high melting points

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52
Q

why is lone pair repulsion present

A

-lone pairs around the central atom provide additional repulsive forces
-for every lone pair present the bond angle between covalent bonds is reduced by 2.5 degrees

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53
Q

v - shaped structure

A

-2 bonding pairs
-2 lone pairs
-104.5 degrees

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54
Q

pyramidal

A

-3 bonding pairs
-1 lone pair
-107 degrees

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55
Q

Explain what causes molecules to have shapes

A

-Molecules have shapes as the bonding and lone pairs repel each other as far apart as possible to reach a position of minimum repulsion and maximum separation

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56
Q

which has a bond angle of 109.5 degrees

A

Diamond

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57
Q

Explain why CF4 has a bond angle of 109.5 degrees

A

the central atom is surrounding 4 bonding pairs of electrons, Therefore they reach positions of maximum separation and minimum repulsion forming a tetrahedral shape

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58
Q

Explain how the electron pair repulsion theory can be used to deduce the shapes of the bond angle in PF3

A

-P has 5 electrons in the valence shell so needs 3 electrons to have a full outer shell
-the central atom of P is surrounding 3 fluorine bonds and has 1 lone pair
-this repels to positions of maximum separation and minimum repulsion
-the angle is 120 degrees and the shape is trigonal planar

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59
Q

what is the shape of an molecule with 2 lone pairs

A

104.5 degrees
-bent shape / v-shaped

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60
Q

what is the shape of a molecule with 1 lone pair

A

107 degrees
pyramidal

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61
Q

what are electron pairs

A

clouds of negative charge, so there is repulsion between them, forcing them as far apart as possible thus causing molecules to have a shape

(equal replusion between electron pairs)

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62
Q

what is the order of repulsion strength in terms of lone and bonding pairs

A

Lone pair–lone pair repulsion is greater than lone pair–bond pair repulsion, which is greater than bond pair–bond pair repulsion.

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63
Q

what are bond angles and when do they stop repelling

A

-the extent to which bonding pairs repel eachother results in a certain angle between them

-Bonds will stop repelling each other when there is maximum separation between bonds and minimum repulsion between pairs of electrons

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64
Q

linear

A

180 degrees
2 bonding pairs

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65
Q

trigonal planar

A

120 degrees
3 bonding pairs

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66
Q

tetrahedral

A

109.5 degrees
4 bonding pairs

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67
Q

trigonal bipyramidal

A

90 and 120 degrees
5 bonding pairs

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68
Q

octahedral

A

90 and 90 degrees
6 bonding pairs

69
Q

what is VSEPR

A

valence shell electron pair repulsion theory

70
Q

steps to calculating shapes of molecules

A

1) identify central atoms

2) count the central atom’s valence electrons

3) Add one electron for each bonding atom

4) Divide number of electrons by 2 to find total

5) number each electron pair

6) use this to predict the shape

71
Q

what are double and triple bonds considered as

A

single bonds
–> called bonding groups

72
Q

why do lone pairs have a stronger repulsion than bonding pairs

A

-lone pairs are held closer to the central atom than bonding pairs. This means that they have a stronger repelling effect than bonding pairs

73
Q

what is the shape of ammonia

A

pyramidal

74
Q

when calculating shapes of molecules what do you do when there is a positive ion

A

subtract 1electron

75
Q

can ionic compounds dissolve in water (soluble aq) and why

A

yes because of the polarity of water that attract the positive and negative ions thus breaking up the structure

76
Q

features of graphite

A

-low density
-layers can slide
-high melting point
-insoluble
-can conduct electricity

77
Q

what shape is formed with 3 bond pairs and 2 lone pairs

A

trigonal planar

78
Q

what shape is formed with 4 bond pairs and 2 lone pairs

A

square planar

79
Q

What shape if H2F+

A

v-shaped

80
Q

Explain the bond angle of H2O

A

104.5
-2 lone pairs which repel more than bonding pairs so bond angle reduces by 5 degrees

81
Q

which is the most likely bond angle around the oxygen atom in ethanol

A

104.5 degrees

82
Q

explain the bond angle in PF3

A

-central atom P has 5 electrons in valence shell
-needs 3 electrons from 3 F atoms
-PF3 has 3 bond pairs and one lone pairs
-lone pairs repel more than bonding pairs
-shape is tetrahedral with bond angle of 107

83
Q

suggest one reason why electron pair repulsion theory cannot be used to predict shape of Cobalt chloride ion

A

too many electrons in d subshell

84
Q

true or false when drawing molecules that are ions brackets have to been drawn

A

true

85
Q

how can dative covalent bonds be demonstrated

A

dot and cross
line diagram

86
Q

how is a normal bond shown

A

bond lies in the plane of the paper

87
Q

how is a dashed bond shown

A

bond extends backwards away from the viewer

88
Q

how is a wedged bond shown

A

bond protrudes towards the viewer

89
Q

tetrahedral shape (drawing)

A

1 dashed line
1 wedge
2 normal lines

90
Q

trigonal bipyramid (drawing)

A

1 wedge
3 normal lines
1 dashed

91
Q

octahedral (drawing)

A

2 wedges
2 dashed
2 normal

92
Q

trigonal planar (drawing)

A

3 normal

93
Q

when does dative covalent occur

A

Dative covalent bonding occurs when one atom in a bonding molecule donates a pair of electrons to another atom. The other atom’s electrons are not involved in the bonding

94
Q

steps for drawing dative covalent bonds

A

1) identify where the lone pair is donated from

2) draw the dot and cross diagram between carbon and oxygen

95
Q

what does an electron dense map indicate

A

the region where you are most likely to find an electron

When the electron cloud is polarised, the electron cloud moves towards a positive region

96
Q

define polarisation

A

the distortion of an electron cloud towards a region of positive charge

97
Q

true or false - same atoms in a molecule are polarised

A

false - only different atoms in a molecule are polarised

98
Q

define polar covalent bonding

A

bonding between atoms with different values of electronegativity

99
Q

define ionic bonding with polarisation

A

small, highly charged cations causing partial covalency

100
Q

factors that influence polarisation in ionic bonds

A

small cation that is highly charged, large anion that is easily polarised

-most ionic = lowest polarisation + larger radius

101
Q

why does polarisation occur

A

-In a covalent bond between two different elements, the electron density is not shared equally

-polarisation is due to a difference in each elements electronegativity

102
Q

define electronegativity

A

the ability of an atom to attract the bonding electron pair in a covalent bond

103
Q

what does it mean if an element has a greater electronegativity

A

greater ability to attract the electron cloud and bonding pair of electrons

104
Q

what element has the greatest electronegativity

A

Flourine

105
Q

what is the trend in electronegativity down a group

A

decreases

106
Q

trend in electronegativity across a period

A

increases

107
Q

why do noble gases have no electronegativity

A

do not form covalent bonds

108
Q

how is a bond considered polar

A

bond must have a difference in electronegativity greater than 0.5and less than 1.7

109
Q

how is a bond considered non-polar

A

difference in electronegativity is less than 0.5

110
Q

what is the difference in electronegativity for ionic bonds

A

more than 1.7

111
Q

charges of electronegative atoms

A

the more electronegative atom has a partial negative charge

-the less electronegative atom has a partial positive charge

112
Q

molecule polarity

A

-A molecule which has symmetrical polar bonds cancel out the dipoles and the molecule is non-polar

-A molecule which has asymmetrical polar bonds are polar

-The presence of lone pairs makes a molecule polar e.g water

113
Q

predicting which molecule is polar

A

1) Does it contain polar bonds or not

2) Are there lone pairs on the central atom

3) Are atoms bonded to the same central atom

114
Q

what causes a permanent dipole

A

a polar molecule

115
Q

define a dipole

A

a difference in charge between two atoms caused by a shift in electron density

116
Q

what are the most common elements for increasing electronegativity

A

H - C - N - Cl - O - F

117
Q

what shape is carbon dioxide

A

linear
180 degrees

118
Q

what does a higher difference in electronegatvity mean

A

molecule is more ionic

119
Q

complete the sentence
the larger the electronegativity difference

A

the larger the dipole

120
Q

what scale is used for electronegativity

A

the pauling scale

121
Q

what does a larger difference in electronegativity mean

A

The greater the difference in electronegativity, the more polarized the electron distribution and the larger the partial charges of the atoms.

122
Q

correlation between bond strength and length

A

single bond = weakest (longer)
double bond = stronger (shorter)

123
Q

bonding in covalent molecules

A

Covalent bonds between atoms in a molecule are relatively strong however, the intermolecular forces between molecules are weak.

124
Q

what are the 3 types of intermolecular forces

A

-hydrogen bonding
-permanent dipole-permanent dipole
-van der waal forces

125
Q

van der waal forces

A

-exist between ALL covalent molecules (polar and non-polar except diamond)

-When two atoms in a molecule meet there will be an attraction between the electron cloud and nuclei of the atoms. There will also be repulsion between both of the nuclei and clouds of electrons

-dipole –> a bond whose ends have opposite charges

-van der waal forces are the weakest intermolecular forces

126
Q

how do van der waal forces form

A

1) A non-polar molecule has an uneven distribution of electron cloud

2) The electron cloud has temporarily been displaced to one end

3) An instantaneous dipole is formed

4) A dipole in one molecule induces a dipole in another due to electrostatic attraction

5) Van der waal forces are formed

127
Q

factors affecting van der waal forces

A

-number of electrons (more electrons = stronger forces)

-Points of contact (straight chain rather than branched)

128
Q

why would there be a higher possibility of temporary induced dipoles

A

The larger the atom, the higher the polarizability. As the molecules get bigger there are more electrons so have a higher polarizability and therefore a higher possibility for temporary induced dipoles.

129
Q

Permanent dipole-permanent dipole

A

-Only found in polar molecules

-If a molecule is polar due to its shape, it is said to have a permanent dipole due to a difference in electronegativity

-Between the molecules of HCl there is a difference in electronegativity due to bond polarity. Dipoles dont cancel out and therefore molecules have an overall dipole.

-If molecules contain bonds with a permanent dipole, the molecules may align so there is electrostatic attraction between the opposite charges on neighboring molecules

130
Q

key features of a permanent dipole-permanent dipole interaction

A

-Polar molecules

-strong electrostatic attraction

-stronger than van der waal forces as it is permanent not temporary

-if van der waal forces have a larger boiling point than permanent dipole forces then the van der waal forces exerts the greater influence in this case

131
Q

Explain why only van der waal forces exist in SiF4

A

-SiF4 is a non-polar molecule so has a symmetrical arrangement which means dipoles cancel out
-Temporary dipole is formed by an instantaneous dipole
-dipole induces in a neighbouring molecule due to electrostatic attraction

132
Q

explain how permanent dipole-dipole forces arise between HCl molecules

A

-Difference in electronegativitiy leads to bond polarity
-permanent dipole forms between opposite charges on neighbouring molecules

133
Q

Lone pairs for electronegative atoms

A

N = one lone pair
F = one lone pair
O = two lone pairs

134
Q

what is the strongest intermolecular force

A

hydrogen bonding

135
Q

what elements does hydrogen bonding only occur between

A

-Can only form with Nitrogen, Flourine and Oxygen as there is a significant difference in electronegativity

136
Q

why can only N,O,F form hydrogen bonds with hydrogen

A

-very electronegative

-have a small atomic radius

-therefore makes a more polar bond

137
Q

how are hydrogen bonds formed

A

The more electronegative atom e.g oxygen will attract the electrons more strongly away from the hydrogen. The covalent bond becomes polarised.

When the polarised bond is near a neighbouring molecule that has also been polarised by hydrogen will cause the two molecules to become attracted to eachother thus forming a hydrogen bond.

138
Q

what are the steps to drawing hydrogen bonds

A

1) draw O H O in a straight line
2) Draw hydrogen bonding and one full covalent
3) Add in lone pairs and partial charges
4) Add in rest of the molecule

139
Q

what do temporary dipoles cause

A

an attraction

140
Q

state the strongest intermolecular force in an ice crystal

A

hydrogen bonding (water)

141
Q

explain why iodine has a higher melting point than flourine

A

-iodine = larger atomic radius
-therefore has more electrons = stronger van der waal forces
-more energy required to overcome

142
Q

what is the shape of NH2-

A

v-shaped/bent
104.5

143
Q

why does magnesium have a much greater liquid range

A

forces of attraction in a molten metal are stronger

144
Q

Describe the structure and bonding of graphite and explain why the melting point is very high

A

-each carbon atom covalently bonded to 3 other forming layers of hexagonal rings
-layers held by van der waal forces
-delocalised electrons able to flow through layers
-high melting point to overcome covalent bonds

145
Q

define allotropes

A

different forms of the same element

146
Q

what are the allotropes of carbon

A

diamond, graphite, graphene, fullerene, buckminister fullerene, nanotubes

147
Q

what affects physical properties

A

bonding
crystal structure

148
Q

Diamond

A

-Giant covalent structure

-each carbon atom bonded by covalent bonds to 4 other carbon atoms

-Rigid 3D structure

-Very strong

-Does not conduct electricity

149
Q

Graphite

A

-macromolecular crystal

-each carbon atom is covalently bonded to 3 other in the same 2D plane thus forming hexagonal rings in layers

-Layers of graphite held weakly together by van der waal forces

-conducts electricity as for each carbon atom there is 1 delocalised electron

-delocalized electrons flow within a layer

-120 degrees bond angle (trigonal planar)

150
Q

Graphene

A

-thinnest (1 layer of graphite)

-no van der waal forces only covalent bonds

-light weight and transparent

-good conductor (delocalised electrons for each C atom)

-3 carbon covalent bonds for each carbon

-120 degrees bond angle (trigonal planar)

151
Q

fullerenes

A

-buckministerfullerene contains 60 carbon atoms –> each of which is bonded to 3 others by two single bonds and one double bond

-carbon nanotubes are another type of fullerene –> used to transport drugs to cells in the body and as components in electrical transistors

152
Q

name the type of bond formed between N and Al

A

dative covalent bond

153
Q

metallic structure

A

-Electrostatic attraction between metal cations in a lattice and a sea of delocalised electrons

-For every 1 cation 1 electron will be delocalised

154
Q

why do metallic structures have a high melting point

A

-lattice structure

-strong attractions within lattice structure

-a lot of energy required to overcome the electrosatic force of attraction between cations and electrons

155
Q

factors affecting melting point

A

-nuclear charge

-ionic radius

-attraction

156
Q

hydrogen bonding

A

-soluble in water
-high melting and boiling point

157
Q

what IMF forces are present in a NaCl lattice

A

permanent-dipole-permanent dipole –> polar

158
Q

describe how the intermolecular forces arise in Cl2

A

-van der waal interaction arise due to uneven distribution in electron cloud
-results in instantaneous dipole
-the end of molecule will induce dipole in another molecule due to electrostatic attraction

159
Q

Explain how the value of the bond angle in AlCl3 changes by the formation of the compound H3NAlCl3

A

Aluminium now surrounded by 4 bonding pairs
tetrahedral
109.5 degrees

160
Q

which species had one or more bond angles of 90 degrees

A

ClF4-

161
Q

permanent dipole-permanent dipole

A

The electron distribution in a covalent bond between elements with different electronegativities will be unsymmetrical. This produces a polar covalent bond, and may cause a molecule to have a permanent dipole.

162
Q

why are positive ions smaller

A

greater p:e ratio

163
Q

define covalent bond

A

shared pair of electrons between non-metal atoms

164
Q

soluble vs insoluble

A

ionic = soluble

simple covalent, macromolecular, metallic = insoluble

165
Q

square planar

A

90 degree bond angle
4 bond pair
2 lone pair

166
Q

what is the angle/shape of a bond with 5 bond pairs and 3 lone pairs

A

linear (180)

167
Q

no dipole =

A

no polarity

168
Q

is a C-H bond polar or non-polar

A

non-polar

169
Q

what helps salts separate from water

A

ion-dipole forces
hydrated ions seperate leaving ions by themseleves

e.g potassium iodide in water forms K+ and IOH

Aqa a level chemistry (18 decks)

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