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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
Trends across a period
Values increase Atomic radius increases Increased electron shielding Outer electrons are further from the nucleus
26
Outer shell electrons are in the same shell so no additional shielding =
Greater ‘pulling power’
27
Effect of the number of protons in the nucleus
Electronegativity increases across a period
28
Effect of distance from the nucleus
Electronegativity falls as you go down a group
29
Effect of the amount of shielding by inner electrons
Electronegativity falls as you go down a group
30
What happens in a purely ionic bond
Electrons are completely transferred
31
What happens in a purely covalent bond
Electrons are equally shared
32
When is a bond 100% covalent??
When two identical atoms are bonded together
33
What happens if the atoms that are sharing electrons are different??
The shared electrons will be drawn slightly closer to the more electronegative atom
34
What are intermolecular (London) forces??
Weak interactions between dipoles of different molecules
35
What are the three main categories of intermolecular forces in order of strength??
Induced dipole-dipole interactions Permanent dipole-dipole interactions Hydrogen bonding
36
What are induced dipole-dipole interactions??
Weak intermolecular forces that exist between all molecules (non-polar and polar)
37
When do induced dipole-dipole interactions act??
They act between induced dipoles
38
Are induced dipole-dipole interactions temporary or permanent
Temporary
39
What can happen in an instant in an induced dipole-dipole interaction??
In an instant the induced dipole may disappear and the process may happen again between different molecules
40
What happens when the number of electrons in each molecule increases
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
What is the movement of electrons like in an instantaneous dipole-induced dipole attraction?
The electrons in a molecule are constantly moving
42
What is the affect of an instantaneous dipole-induced dipole attraction on neighbouring molecules
This dipole will induce dipoles in neighbouring molecules which in turn induce dipoles in their neighbours
43
What results in a small instantaneous dipole in an instantaneous dipole-induced dipole attraction?
An uneven distribution of charge
44
Permanent dipole - permanent dipole attractions
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
How is a molecule with an overall dipole described??
Polar
46
If a molecule has a very small or no dipole then how is it described??
It is described as non-polar
47
What is a simple molecular substance??
Made up of simple molecules
48
What structure do simple molecules form in a solid state??
A regular structure called a simple molecular lattice
49
Simple molecular lattice
Molecules held together by weak intermolecular forces Atoms within each molecule are bonded together strongly by covalent bonds
50
What forces are acting on the noble gases
Instantaneous dipole-induced dipole attractions are the only forces acting between atoms
51
Noble gases group trend
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
What is the effect of electron number increasing with noble gases when descending down the group
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
Hydrogen bonds
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
What does the strength of a hydrogen bond depend on??
The strength of an individual hydrogen bond depends on the electronegativity of the atom bonded to H
55
Is ice more or less dense than water
Ice is less dense than water
56
Why is ice less dense than water (bond explanation)
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
Why does water have an unexpectedly high mp/bp??
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
What is enthalpy change??
The energy required to convert one mole of a substance from liquid to gaseous state
59
Why does water have an unusually high surface tension??
Because of strong hydrogen bonds across the surface of the water
60
What is electronegativity??
The ability of an atom to attract the bonding pair of electrons in a covalent bond
61
Percentage of ionic character equation
% ionic character = 100 x (difference in electronegativity) / 3.3
62
What is a polar bond??
A covalent bond with a permanent dipole, having partial positive and negative charges on bonded atoms
63
What is an overall dipole??
Has a shape that results in charge being separated between two ends of the molecule
64
What is responsible for the anomalously high boiling points of ammonia, water and hydrogen fluoride??
Hydrogen bonds
65
What are the forces acting between molecules of water?
A hydrogen bond is forming by attraction between delta + and delta - charges on different water molecules
66
Why are bonds equidistant from each other??
All electron pairs repel equally so each bond is equidistant from each other
67
What is VSEPR (valence shell electron repulsion theory)???
Molecules adapt the shape that is most stable This is achieved when the electron pairs are as far apart as possible
68
Tetrahedral shape explanation
4 identical bonds equally spaced around the central atom
69
Bond angle of a tetrahedral shape
109.5 degrees
70
Triganol planar shape explanation
3 identical bonds equally spaced around the central atom
71
Trigonal planar bonding angle
120 degrees
72
Pyramidal shape explanation
1 lone pair repels the bonding pairs more, skewing the overall shape Has 4 electron pairs: 3 bonding pairs and 1 lone pairs
73
Bond angle of a pyramidal shape
107 degrees
74
Non-linear shape explanation
2 lone pairs repel bonding pairs further meaning the bond angle is smaller 4 electron pairs: 2 bonding pairs and 2 lone pairs
75
Non-linear bonding angle
104.5 degrees
76
What is the general rule for bonding angle decreasing
When a lone pair of electrons is added, the bonding angle decreases by 2.5
77
Octahedral shape explanation
6 identical bonding pairs
78
Octahedral bonding angle
90 degrees
79
Linear shape explanation
2 identical bonding regions as far from each other as possible
80
Bonding angle of linear shape
180 degrees
81
Why can elements in period 3 and below have more than 8 electrons in their outer shell
There are empty available d orbitals that can be used
82
Why can sulfur form 6 covalent bonds??
Sulfur has empty available 3D orbitals in to which 2 of sulfur’s outershell electrons can be promoted
83
Why does hydrogen chloride have intermediate bonding??
Because they have permanent dipole dipole interactions The electrons are not equally shared because the hydrogen and chloride atoms have different electronegativities
84
Structure of ionic bonding
Giant lattice
85
Properties of ionic bonding
Ionic bonds between ions Ions held together by strong electrostatic forces between oppositely charged ions High mp/bp Strong and hard
86
Why can ionically bonded molecules conduct when molten or dissolved but not when solid
When molten/dissolved ions are free to move When solid, ions are fixed in a lattice structure
87
Metallic structure
Giant lattice
88
Properties of metallic bonding
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
Why are metallically bonded molecules good conductors of heat??
Because delocalised electrons are free to move
90
Covalent structure
Giant lattice Giant layer lattice Simple molecular Simple molecular - hydrogen bonded Polymers
91
Properties of covalently bonded molecules (giant lattice)
Covalent bonds between atoms High mp/bp Strong and hard Insoluble Not conductive
92
Properties of covalently bonded molecules (giant layer lattice)
Covalent bonds between atoms in layers Instantaneous dipole:induced dipoles forces between layers High mp/bp Soft solids Insoluble Conducts electricity
93
Properties of simple molecular substances
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
Properties of hydrogen bonded simple molecular substances
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
Properties of polymers
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

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