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Y11 Chemistry > Topic 2: Combining Atoms and Molecules > Flashcards

Topic 2: Combining Atoms and Molecules Flashcards

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1
Q

What is a mole (m)?

A

Unit of measurement; amount of a material containing 6.02 x 10^23 elementary particles.

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2
Q

What is Avogadro’s number?

A

N_A = 6.02 x 10^23

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3
Q

Formula for number of molecules in a sample?

A

N = n x N_A
where:
- N = number of molecules in sample
- n = number of moles in sample
- N_A = Avogadro’s number

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4
Q

Formula for number of moles in a sample?

A

n=m/M
where:
- n = number of moles in sample
- m = mass of sample
- M = molar mass

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5
Q

Formula for determining percentage composition?

A

% composition = ((M_element x N_atoms of that element)/M_compound) x 100

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6
Q

What is an empirical formula?

A

The simplest whole number ratio of atoms in a certain molecule.

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7
Q

What is a molecular formula?

A

The actual number of atoms in a certain molecule.

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8
Q

When does covalent bonding occur?

A

When valence electron pairs are shared by non-metallic atoms.

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9
Q

Describe a covalent bond.

A

The strong electrostatic attraction that arises between a bonding pair of valence electrons and positively charged nuclei of both participating atoms.

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10
Q

What is a single covalent bond? Give an example.

A

2 atoms sharing one pair of electrons to complete their octet. e.g. 2 chlorine atoms (because Group VII elements have 7 electrons).

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11
Q

What is a double covalent bond? Give an example.

A

2 atoms sharing two pairs of electrons to complete their octet. e.g. 2 oxygen atoms (because Group VI elements have 6 electrons).

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12
Q

What is a triple covalent bond? Give an example.

A

2 atoms sharing three pairs of electrons to complete their octet. e.g. 2 nitrogen atoms (because Group V elements have 5 electrons).

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13
Q

How does the strength of the intramolecular attraction of a covalent bond increase?

A

With an increase in the number of bonding pairs of valence electrons.

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14
Q

Order the three types of covalent bonds by means of weakest to strongest.

A
  1. Single
  2. Double
  3. Triple
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15
Q

What happens to the amount of energy required to break the covalent bond as the bond strength increases?

A

It also, correspondingly, increases.

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16
Q

What is an intramolecular force?

A

Force occurring between atoms within a molecule.

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17
Q

What is an intermolecular force?

A

Force occurring between different molecules.

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18
Q

What are homonuclear molecules?

A

Molecules comprised of atoms of the same element.

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19
Q

What are heteronuclear molecules?

A

Molecules comprised of atoms of differing elements.

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20
Q

What is electronegativity?

A

A measure of the tendency of an atom, of a given chemical element, to attract a bonding pair of electrons.

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21
Q

Define bond polarity.

A

The distribution of electron density and thus, electric charge, across a chemical bond between two atoms.

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22
Q

What does bond polarity depend on?

A

On the electronegativities of the bonded atoms.

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23
Q

Describe non-polar covalent bonds.

A

Electrons are shared equally between two atoms. No partial charge/dipole is introduced as the charges are equally distributed.

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24
Q

How do non-polar covalent bonds occur?

A

From the combination of two non-metallic atoms, of the same electronegativity, sharing electrons. Bonding electrons have equal attraction to both positive nuclei, and are therefore held an equal distance apart.

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25
Q

Describe polar covalent bonds.

A

Unequal sharing of electron pair occurs. So, polar covalent bonds are charged/partially charged.

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26
Q

How do polar covalent bonds occur?

A

From the sharing of bonding electrons between atoms of differing electronegativities. The bonding electron pair is displaced towards the more electronegative atom than the less electronegative atom.

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27
Q

What are partial charges denoted by?

A

Delta denotation (δ).

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28
Q

What is a partial charge?

A

An electric charge that has no fixed value - always being less than a formal +1 charge - caused by a polar covalent bond.

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29
Q

Which atom in a polar covalent bond has a partial-negative (δ-) charge?

A

The more electronegative atom.

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30
Q

Which atom in a polar covalent bond has a partial-positive (δ+) charge?

A

The less electronegative atom.

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31
Q

What happens to chemical bonds as they increase in polarity?

A

They transform from pure covalent to ionic.

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32
Q

What is the relationship between:
- Electronegativity difference between bonding atoms of a covalent bond
- Bond polarity
- Partial charge?

A

They have a directly proportional relationship.
Greater electronegativity difference between bonding atoms -> Greater bond polarity -> Greater partial charges.

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33
Q

What is covalence?

A

Refers to the number of valence electron pairs that an atom can share with its neighbouring atoms.

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34
Q

Which atom has the highest covalence in a molecule?

A

Central atom (so, also usually element of lowest electronegativity).

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35
Q

What are continuous covalent networks?

A

Large, rigid 3D arrangements of atoms held together by strong covalent bonds in a network lattice. ‘Continuous’ refers to how no. of atoms is not fixed, unlike molecules.

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36
Q

What are molecules?

A

Discrete units, comprised of a fixed no. of atoms bonded together by covalent bonds.

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37
Q

What does it mean (generally) if the electronegativity difference between atoms is less than 0.4?

A

Non-polar covalent bond.

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38
Q

What does it mean (generally) if the electronegativity difference between atoms is greater than 0.4?

A

Polar covalent bond.

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39
Q

Recall the two steps of writing systematic molecular names of covalent compounds.

A
  1. Identify and name central atom.
  2. Identify and name bonded atom, ensuring suffix is replaced with ‘ide’ and numerical prefixes are used to specify no. of atoms.
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40
Q

What numerical prefix is assumed and not written?

A

‘Mono-‘ (meaning 1)

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41
Q

What are the physical properties of continuous covalent network solids?

A
  • Hard materials.
  • Extremely high melting and boiling points.
  • Poor conductors of electricity.
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42
Q

Why can continuous covalent network solids withstand high degrees of mechanical stress?

A

Because covalent bonds are extremely strong, and thus require an extremely high amount of energy to break.

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43
Q

Why do continuous covalent network solids have high melting/boiling points?

A

Due to strong nature of covalent bonding, significant quantity of thermal energy is required to disrupt repeating interactions within covalent lattice enough to break bonds.

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44
Q

Why are continuous covalent network solids poor conductors of electricity?

What material is an exception? Explain.

A

As all valence electrons are involved in covalent bonds.

Graphite is an exception, as only three out of four valence electrons in the carbon atoms are involved in covalent bonds, leaving the fourth valence electron to be delocalised.

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45
Q

What does the VSEPR theory state?

A

That the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs are oriented as far apart as possible.
So, atoms within molecules are arranged into positions which minimise repulsion around the central atom.

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45
Q

What does ‘VSEPR’ in VSEPR theory stand for?

A

Valence Shell Electron Pair Repulsion.

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46
Q

What type of electron pair exhibits greatest repulsion?

A

Non-bonded electron pairs (lone pairs).

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46
Q

What type of electron pair experiences the least repulsion?

A

Bonded electron pairs.

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47
Q

What are lone pairs?

A

Paired electrons that are not shared in a covalent bond - thus, non-bonding electron pairs.

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48
Q

What are bonded electron pairs?

A

A pair of electrons shared in a covalent bond between two atoms.

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49
Q

What are the 5 common molecular shapes?

A

Linear, V-shaped/bent, trigonal pyramidal, tetrahedral, and trigonal planar.

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50
Q

What molecular shape/s can a 3 atom molecule be?

A

Linear or V-shaped/bent.

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51
Q

What molecular shape is a 2 atom molecule?

A

Linear.

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52
Q

What molecular shape/s can a 4 atom molecule be?

A

Trigonal planar or trigonal pyramidal.

53
Q

What molecular shape is a 5 atom molecule?

A

Tetrahedral.

54
Q

What molecular shape is a 3 atom molecule with a lone pair on the central atom?

A

V-shaped/bent.

55
Q

What molecular shape is a 3 atom molecule without a lone pair on the central atom?

A

Linear.

56
Q

What molecular shape is a 4 atom molecule with a lone pair on the central atom?

A

Trigonal pyramidal.

57
Q

What molecular shape is a 4 atom molecule without a lone pair on the central atom?

A

Trigonal planar.

58
Q

What are the three steps to drawing molecular shapes?

A
  1. Count no. of atoms and identify elements involved.
  2. Identify central atom and find the no. of bonding and non-bonding electrons.
  3. Determine 3D shape of molecule.
59
Q

Describe linear molecular shape.

A

2 bonded atoms to the central atom, no lone pairs, 180 degree bond angle.

60
Q

Describe V-shaped/bent molecular shape.

A

2 bonded atoms to the central atom, 1 lone pair, 120 degree bond angle.

61
Q

Describe trigonal pyramidal molecular shape.

A

3 bonded atoms to the central atom, 1 lone pair, 107.5 degree bond angle.

62
Q

Describe tetrahedral molecular shape.

A

4 bonded atoms to the central atom, no lone pairs, 109.5 degree bond angle.

63
Q

Describe trigonal planar molecular shape.

A

3 bonded atoms to the central atom, no lone pairs, 120 degree bond angle.

64
Q

Prefix for 1 carbon?

A

Meth-

65
Q

Prefix for 2 carbons?

A

Eth-

66
Q

Prefix for 3 carbons?

A

Prop-

67
Q

Prefix for 4 carbons?

A

But-

68
Q

Prefix for 5 carbons?

A

Pent-

69
Q

Prefix for 6 carbons?

A

Hex-

70
Q

Prefix for 7 carbons?

A

Hept-

71
Q

Prefix for 8 carbons?

A

Oct-

72
Q

Prefix for 9 carbons?

A

Non-

73
Q

Prefix for 10 carbons?

A

Dec-

74
Q

What is a polar molecule?

A

A molecule in which the charges are unevenly distributed.

75
Q

What is a non-polar molecule?

A

A molecule that shares electrons equally and does not have oppositely charged ends.

76
Q

What is a method of determining the overall polarity of a molecule?

A

Identify the centres of positive and negative electric charge within the molecule.

77
Q

What does it mean when the centres of positive and negative charge are in the same location?

A

The electric charge distribution is even, the molecule has no electric dipole, and so, the molecule is non-polar.

78
Q

What does it mean when the centres of positive and negative charge are in different locations?

A

The electric charge distribution is uneven, an electric dipole is introduced, and so, the molecule is polar.

79
Q

What are primary bonds also called?

A

Intramolecular forces

80
Q

What are secondary interactions also called?

A

Intermolecular forces.

81
Q

Which is weaker: primary bonds or secondary interactions?

A

Secondary interactions are significantly weaker than primary bonds.

82
Q

What are 2 factors that determine physical properties?

A
  • Molecular size
  • Polarity
83
Q

What are the 3 types of intermolecular forces?

A

1) Dispersion forces
2) Dipole-dipole interactions
3) Hydrogen bonding

84
Q

What are dispersion forces?

A

Weak forces of attraction which exist between 2 temporary dipoles.

85
Q

How do temporary dipoles come about?

A

Electrons are constantly in motion; therefore, there is a high probability of electrons becoming asymmetrically distributed. Thus, when there is a negative charge on one end and a positive charge on the other end, a temporary dipole arises (regardless of whether a molecule is polar or non-polar).

86
Q

What causes the strength of the force of attraction to increase?

A

An increase in the size of the molecule.

87
Q

What are dipole-dipole interactions?

A

Relatively strong forces of attraction that exist between 2 polar molecules (permanent dipoles).

88
Q

What is hydrogen bonding?

A

The strongest intermolecular force, which is a type of dipole-dipole interaction.

89
Q

When does hydrogen bonding occur? Why?

A

Occurs only between polar molecules where a hydrogen atom is directly bonded to either a nitrogen, oxygen, or fluorine atom, due to their high electronegativities.

90
Q

Order the 3 types of intermolecular forces from weakest to strongest.

A
  1. Dispersion forces
  2. Dipole-dipole interactions
  3. Hydrogen bonding
91
Q

What are hydrocarbons?

A

A category of organic molecules consisting of carbon chemically combined with hydrogen.

92
Q

Describe the nature of the bonds of hydrocarbons.

A

Covalent and non-polar.

93
Q

Why are hydrocarbons often fuels?

A

As they store chemical energy within covalent bonds between their atoms; so, they may release energy, to be used as fuel, when combusted.

94
Q

What is combustion?

A

A chemical reaction wherein a fuel (hydrocarbon) reacts with an oxidiser at high temperatures.

95
Q

What is an oxidiser?

A

Any chemical which gains electrons in a chemical reaction.

96
Q

What are the 2 types of combustion?

A

Complete and incomplete.

97
Q

Describe the general 3 steps of combustion.

A

1) The oxidiser removes electrons from covalent bonds within hydrocarbon molecules.
2) This removal of electrons from covalent bonds is accompanied by the release of stored chemical energy.
3) Released energy is transformed into light and heat, which radiate away from the site of reaction.

98
Q

What is complete combustion?

A

Combustion that occurs when hydrocarbons react with sufficient oxygen (O2) molecules to produce carbon dioxide (CO2) and water (H2O).

99
Q

What is incomplete combustion?

A

Combustion that occurs when there are insufficient oxygen molecules (O2) present for hydrocarbons to react with; so, the reaction produces water (H2O), carbon monoxide (CO), and elemental carbon (C).

100
Q

What are the 2 factors that determine physical properties of hydrocarbons?

A
  • Size of the molecule
  • Length of the hydrocarbon chain
101
Q

What happens as the length of a hydrocarbon chain increases? Why?

A

The hydrocarbon’s boiling/melting points increase.
The non-polar portion of the molecule, and the molecular size, also increase.
Because as the number of carbon atoms increases, so does the number of sites (atoms) over which dispersion forces act between molecules.

102
Q

What is a functional group?

A

A group of atoms responsible for the characteristic chemical reactions of a particular molecule.

103
Q

What are homologous series?

A

Group of molecules with the same functional group and therefore similar chemical properties, but with differing physical properties due to variation in the length of their carbon chains.

104
Q

What are three types of hydrocarbons?

A

Alkanes, alkenes, and alkynes.

105
Q

What are alkanes?

A

Homologous series of hydrocarbons with a functional group of a carbon-carbon single covalent bond. Saturated. All names end in ‘-ane’.

106
Q

What is the general chemical formula alkanes adhere to?

A

CnH2n+2

107
Q

What are alkenes?

A

Homologous series of hydrocarbons with a functional group of a carbon-carbon double covalent bond. Unsaturated. All names end in ‘-ene’.

108
Q

What is the general chemical formula alkenes adhere to?

A

CnH2n

109
Q

What are alkynes?

A

Homologous series of hydrocarbons with a functional group of a carbon-carbon triple covalent bond. Unsaturated. All names end in ‘-yne’.

110
Q

What is the general chemical formula alkynes adhere to?

A

CnH2n-2

111
Q

What are saturated hydrocarbons?

A

Hydrocarbons that only contain single carbon to carbon bonds (alkanes). This means they contain the maximum number of hydrogen atoms around each carbon atom.

112
Q

What are unsaturated hydrocarbons?

A

Hydrocarbons that contain double or triple carbon to carbon bonds (alkenes/alkynes). This means they contain less than the maximum number of hydrogen atoms around each carbon atom.

113
Q

What type of reaction occurs between an alkene/alkyne and bromine during bromination?

A

Addition reaction.

114
Q

What happens in an addition reaction?

A

Highly electronegative halogen atoms attack a carbon-carbon double/triple bond, removing electrons from said bonds, forming a saturated alkane. Therefore, atoms (e.g. bromine) add to adjacent atoms (e.g. carbon) either side of a double/triple covalent bond.

115
Q

What is bromination?

A

The addition of bromine/bromine water to a hydrocarbon (alkane/alkene/alkyne).

116
Q

How does bromination identify an alkane?

A

Bromine/bromine water is red/brown in colour; an alkane will not react with bromine, and hence, the solution will remain its original red/brown.

117
Q

How does bromination identify an alkene/alkyne?

A

Bromine/bromine water is red/brown in colour; alkenes/alkynes will cause it to lose its original red/brown colour and form a colourless liquid, as alkanes are colourless and odourless.

118
Q

What are alcohols?

A

Derivatives of hydrocarbons, which have a hydroxyl group
(-OH) which has replaced a hydrogen atom. Have suffix ‘-ol’ (e.g. ethanol).

119
Q

What are the 3 types of structural formula?

A
  • Full/extended
  • Condensed
  • Skeletal
120
Q

What are alkyl groups?

A

Groups of carbon atoms (side chains) attached to carbon chains of hydrocarbons.

121
Q

Examples of common alkyl groups?

A

Methyl (CH3), ethyl (CH2CH3).

122
Q

What are polymers?

A

Very large, long-chain molecules of high molecular mass, consisting of repeating units called monomers.

123
Q

How are monomers denoted?

A

By an enclosing square bracket.

124
Q

Why do polymer chains not have double/triple covalent bonds?

A

Because the addition polymerisation process necessary to form a polymer breaks double/triple covalent bonds (addition reaction).

125
Q

What are the 2 groups of polymers?

A

Thermosetting polymers
Thermoplastic polymers

126
Q

What are thermoplastic polymers?

A

Polymers characterised by weak intermolecular forces between individual polymer chains within the material.

127
Q

Why can thermoplastic polymers be softened/recycled?

A

Because they have weak intermolecular forces, these said forces may be overcome by heating the material, with minimal thermal energy, to its melting point. So, the polymer softens and can be reformed in shape.

128
Q

What are thermosetting polymers?

A

Polymers characterised by the presence of covalent bonds between individual polymer chains within the material.

129
Q

Why can thermosetting polymers not be softened/recycled?

A

Because they have strong covalent bonds, they have a more rigid structure, and require more copious amounts of thermal energy to overcome these bonds. So, they do not melt, and combust to form CO2 - charring and burning - before the melting point is reached.

130
Q

Explain interactions between partial negatives and partial positives.

A

Partial positives repel each other, partial negatives repel each other, and partial positives attract partial negatives.
i.e. in polar covalent bonds, such as dipole-dipole interactions, partial negatives interact with partial positives to form these bonds.

131
Q

What are structural isomers?

A

Compounds with the same molecular formula but different structural formula.

Y11 Chemistry (5 decks)

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