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Chemistry > Module 2: Bonding And Structure > Flashcards

Module 2: Bonding And Structure Flashcards

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1
Q

What is a covalent bond?

A

An electrostatic attraction between a shared pair of electrons with a positive nuclei

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2
Q

What does a single bond contain?

A

Two shared electrons and a sigma bond

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3
Q

What does a double bond contain?

A

Four shared electrons and a sigma bond and a pi bond

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4
Q

What does a triple bond contain??

A

Six shared electrons and a sigma bond and 2 pi bonds

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5
Q

How is bond length defined?

A

Defined as the distance between the nuclei of two covalently bonded atoms

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6
Q

How is bond energy (bond enthalpy) defined??

A

Defined as the energy required to break a bond in every molecule in one mole of gaseous molecules

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7
Q

What does the strength of covalent bonding depend on?

A

How many electrons are being shared

The bond length

Any additional ionic character

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8
Q

If the bond energy is small, what is the strength of the covalent bond like?

A

The covalent bond is weak and can easily be broken during a chemical reaction

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9
Q

What is dative covalent bonding??

A

A type of covalent bonding where both shared electrons are donated by the same atom

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10
Q

What is metallic bonding?

A

Electrostatic attraction between the sea of delocalised electrons and the lattice of positive ions

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11
Q

Structure of a metallic bond

A

In metals, the partially filled outer shells all overlap and the outer shell electrons are able to move freely through the metal

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12
Q

Why are the electrons described as delocalised in a metallic bond??

A

The electrons are not localised within individual bonds

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13
Q

Why are metals good conductors of electricity??

A

The outer shell electrons are free to move and carry a current

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14
Q

Why are metals good conductors of heat??

A

When solids get hot, atoms vibrate

In a metal the mobile electrons can carry energy to distant atoms so they can vibrate too so heat can then travel through the metal

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15
Q

Why are metals ductile and malleable??

A

Because delocalised electrons hold the atoms together without making bonds between specific atoms

Therefore it is relatively easy for layers of atoms to slide past each other

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16
Q

Why are metals shiny and can reflect light??

A

Incoming light causes electrons to oscillate and they re-emit energy as light

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17
Q

What is an ionic bond??

A

Electrostatic attraction between a positive ion and a negative ion

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18
Q

Why are most ionic compounds soluble in polar solvents such as water, but some are not??

A

If ions have large charges then the ionic attraction may be too strong for water to break down the lattic structure

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19
Q

Why does solid sodium chloride not conduct electricity but molten sodium chloride does??

A

Because when solid, sodium chloride ions are in a fixed lattice but when molten, the sodium chloride ions dissociate and are free to move past each other and conduct a current

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20
Q

List factors affecting the strength of a covalent bond

4

A

Number of electrons

Bond length

Electron distance from nuclei

Additional ionic character

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21
Q

What is electronegativity??

A

A measure of the tendency of an atom to attract a bonding pair of electrons

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22
Q

The attraction that a bonding pair of electrons feels for a particular nucleus depends on:

A

1) number of protons in the nucleus
2) distance from the nucleus
3) amount of screening/shielding by inner electrons

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23
Q

Trends down a group

A

Values decrease

Atomic radius increases

Increased electron shielding

Outer electrons are further from the nucleus

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24
Q

Less attraction between nucleus and bonding pair of electrons

=

A

Smaller pulling power

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25
Q

Trends across a period

A

Values increase

Atomic radius increases

Increased electron shielding

Outer electrons are further from the nucleus

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26
Q

Outer shell electrons are in the same shell so no additional shielding

=

A

Greater ‘pulling power’

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27
Q

Effect of the number of protons in the nucleus

A

Electronegativity increases across a period

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28
Q

Effect of distance from the nucleus

A

Electronegativity falls as you go down a group

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29
Q

Effect of the amount of shielding by inner electrons

A

Electronegativity falls as you go down a group

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30
Q

What happens in a purely ionic bond

A

Electrons are completely transferred

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31
Q

What happens in a purely covalent bond

A

Electrons are equally shared

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32
Q

When is a bond 100% covalent??

A

When two identical atoms are bonded together

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33
Q

What happens if the atoms that are sharing electrons are different??

A

The shared electrons will be drawn slightly closer to the more electronegative atom

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34
Q

What are intermolecular (London) forces??

A

Weak interactions between dipoles of different molecules

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35
Q

What are the three main categories of intermolecular forces in order of strength??

A

Induced dipole-dipole interactions

Permanent dipole-dipole interactions

Hydrogen bonding

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36
Q

What are induced dipole-dipole interactions??

A

Weak intermolecular forces that exist between all molecules (non-polar and polar)

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37
Q

When do induced dipole-dipole interactions act??

A

They act between induced dipoles

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38
Q

Are induced dipole-dipole interactions temporary or permanent

A

Temporary

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39
Q

What can happen in an instant in an induced dipole-dipole interaction??

A

In an instant the induced dipole may disappear and the process may happen again between different molecules

40
Q

What happens when the number of electrons in each molecule increases

A

The instantaneous and induced dipoles are larger

The dipole-dipole interactions are greater

The attractive forces between molecules are stronger

The induced dipole is larger

There is more energy needed to overcome the intermolecular forces

41
Q

What is the movement of electrons like in an instantaneous dipole-induced dipole attraction?

A

The electrons in a molecule are constantly moving

42
Q

What is the affect of an instantaneous dipole-induced dipole attraction on neighbouring molecules

A

This dipole will induce dipoles in neighbouring molecules which in turn induce dipoles in their neighbours

43
Q

What results in a small instantaneous dipole in an instantaneous dipole-induced dipole attraction?

A

An uneven distribution of charge

44
Q

Permanent dipole - permanent dipole attractions

A

Many molecules have differing electronegativities

The separation of charge is called a dipole

The greater the difference in electronegativity, the greater the dipole will be

45
Q

How is a molecule with an overall dipole described??

A

Polar

46
Q

If a molecule has a very small or no dipole then how is it described??

A

It is described as non-polar

47
Q

What is a simple molecular substance??

A

Made up of simple molecules

48
Q

What structure do simple molecules form in a solid state??

A

A regular structure called a simple molecular lattice

49
Q

Simple molecular lattice

A

Molecules held together by weak intermolecular forces

Atoms within each molecule are bonded together strongly by covalent bonds

50
Q

What forces are acting on the noble gases

A

Instantaneous dipole-induced dipole attractions are the only forces acting between atoms

51
Q

Noble gases group trend

A

On descending the group, the number of electrons increases so the London forces get stronger

So more energy is needed to separate the atoms

Hence mp and bp increase on descending the group

52
Q

What is the effect of electron number increasing with noble gases when descending down the group

A

On descending the group the total number of electrons in each molecule increases so the London forces get stronger so more energy is needed to separate the molecules

As a result mp and bp increases

53
Q

Hydrogen bonds

A

Much stronger than the previous two intermolecular forces

Occurs between any molecule that contains a H+ atom covalently bonded to F, O or N

54
Q

What does the strength of a hydrogen bond depend on??

A

The strength of an individual hydrogen bond depends on the electronegativity of the atom bonded to H

55
Q

Is ice more or less dense than water

A

Ice is less dense than water

56
Q

Why is ice less dense than water (bond explanation)

A

When water freezes, more hydrogen bonds establish

As hydrogen bonds are long bonds, the molecules are held apart from each other
In interlocking hexagons

57
Q

Why does water have an unexpectedly high mp/bp??

A

Water has hydrogen bonds between molecules which are strong

Other group 6 hydrides have weaker intermolecular forces and so need less energy to break

58
Q

What is enthalpy change??

A

The energy required to convert one mole of a substance from liquid to gaseous state

59
Q

Why does water have an unusually high surface tension??

A

Because of strong hydrogen bonds across the surface of the water

60
Q

What is electronegativity??

A

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

61
Q

Percentage of ionic character equation

A

% ionic character = 100 x (difference in electronegativity) / 3.3

62
Q

What is a polar bond??

A

A covalent bond with a permanent dipole, having partial positive and negative charges on bonded atoms

63
Q

What is an overall dipole??

A

Has a shape that results in charge being separated between two ends of the molecule

64
Q

What is responsible for the anomalously high boiling points of ammonia, water and hydrogen fluoride??

A

Hydrogen bonds

65
Q

What are the forces acting between molecules of water?

A

A hydrogen bond is forming by attraction between delta + and delta - charges on different water molecules

66
Q

Why are bonds equidistant from each other??

A

All electron pairs repel equally so each bond is equidistant from each other

67
Q

What is VSEPR (valence shell electron repulsion theory)???

A

Molecules adapt the shape that is most stable

This is achieved when the electron pairs are as far apart as possible

68
Q

Tetrahedral shape explanation

A

4 identical bonds equally spaced around the central atom

69
Q

Bond angle of a tetrahedral shape

A

109.5 degrees

70
Q

Triganol planar shape explanation

A

3 identical bonds equally spaced around the central atom

71
Q

Trigonal planar bonding angle

A

120 degrees

72
Q

Pyramidal shape explanation

A

1 lone pair repels the bonding pairs more, skewing the overall shape

Has 4 electron pairs: 3 bonding pairs and 1 lone pairs

73
Q

Bond angle of a pyramidal shape

A

107 degrees

74
Q

Non-linear shape explanation

A

2 lone pairs repel bonding pairs further meaning the bond angle is smaller

4 electron pairs: 2 bonding pairs and 2 lone pairs

75
Q

Non-linear bonding angle

A

104.5 degrees

76
Q

What is the general rule for bonding angle decreasing

A

When a lone pair of electrons is added, the bonding angle decreases by 2.5

77
Q

Octahedral shape explanation

A

6 identical bonding pairs

78
Q

Octahedral bonding angle

A

90 degrees

79
Q

Linear shape explanation

A

2 identical bonding regions as far from each other as possible

80
Q

Bonding angle of linear shape

A

180 degrees

81
Q

Why can elements in period 3 and below have more than 8 electrons in their outer shell

A

There are empty available d orbitals that can be used

82
Q

Why can sulfur form 6 covalent bonds??

A

Sulfur has empty available 3D orbitals in to which 2 of sulfur’s outershell electrons can be promoted

83
Q

Why does hydrogen chloride have intermediate bonding??

A

Because they have permanent dipole dipole interactions

The electrons are not equally shared because the hydrogen and chloride atoms have different electronegativities

84
Q

Structure of ionic bonding

A

Giant lattice

85
Q

Properties of ionic bonding

A

Ionic bonds between ions

Ions held together by strong electrostatic forces between oppositely charged ions

High mp/bp

Strong and hard

86
Q

Why can ionically bonded molecules conduct when molten or dissolved but not when solid

A

When molten/dissolved ions are free to move

When solid, ions are fixed in a lattice structure

87
Q

Metallic structure

A

Giant lattice

88
Q

Properties of metallic bonding

A

Atoms in a metal are held together in a lattice by strong metallic bonds

Close packed arrangement

High mp/bp

Malleable and ductile

Insoluble

Good conductors

89
Q

Why are metallically bonded molecules good conductors of heat??

A

Because delocalised electrons are free to move

90
Q

Covalent structure

A

Giant lattice
Giant layer lattice

Simple molecular
Simple molecular - hydrogen bonded

Polymers

91
Q

Properties of covalently bonded molecules (giant lattice)

A

Covalent bonds between atoms

High mp/bp

Strong and hard

Insoluble

Not conductive

92
Q

Properties of covalently bonded molecules (giant layer lattice)

A

Covalent bonds between atoms in layers

Instantaneous dipole:induced dipoles forces between layers

High mp/bp

Soft solids

Insoluble

Conducts electricity

93
Q

Properties of simple molecular substances

A

Covalent bonds between atoms in molecules

Instantaneous dipole:induced dipole and maybe permanent dipole-dipole attractions between molecules

Low mp/bp

Solids are soft

Soluble in non-polar solvents

Do not conduct electricity

94
Q

Properties of hydrogen bonded simple molecular substances

A

Covalent bonds between atoms in molecules

Hydrogen bonds and id:id attractions between molecules

Relatively low mp/bp

Solids are stronger and harder than other simple molecules due to hydrogen bonding

Soluble in polar solvents

Do not conduct electricity

95
Q

Properties of polymers

A

Covalent bonds between atoms within polymer molecules

Instantaneous dipole:induced dipole attractions between polymer molecules

Intermediate mp/bp

Soft And easily moulded

Insoluble in polar solvents

Do not conduct

Chemistry (7 decks)

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