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Chemistry > 1.3: Chemical bonding > Flashcards

1.3: Chemical bonding Flashcards

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1
Q

What atoms are generally stable alone, and why?

A
  • Noble gases because they have a stable electronic configuration, they exist stably as monatomic elements
  • These atoms do not need to form bonds in order to become more stable
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2
Q

What do the other atoms have to do with to become more stable?

A

form bonds with themselves, or make compounds with other elements

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3
Q

What is ionic bonding?

A

An electrostatic force of attraction between oppositely charged ions

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4
Q

What do ionic compounds contain?

A

metal and non-metals elements

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5
Q

How does ionic bonding occur?

A

from the transfer of electrons from the outer shell of the metal to form a positively charged cation, to the outer shell of the non-metal which forms a negatively charged anion.

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6
Q

How does magnesium and oxygen form an ionic compound

A

Mg donates their 2 outer shell electrons to the oxygen outer shell. Due to opposite charges, they are attracted to each other so are ions

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7
Q

What are dot and cross diagrams?

A

They are used to represent ionic compounds, the dots and crosses correspond to the outer-shell electrons of different elements.

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8
Q

What are the physical properties of ionic compounds?

A
  • giant lattice structure
  • held together by ions, strong electrostatic forces of attraction between oppositely charged ions.
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9
Q

Do ion compounds have a high or low melting point and boiling point?

A

High

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10
Q

How do ionic compounds have a high melting/boiling point

A

A Lot of energy is needed to overcome the strong electrostatic forces of attraction, between the oppositely charged cations

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11
Q

Are ionic compounds soluble or insoluble in water?

A

soluble in water

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12
Q

How are ionic compounds usually soluble in water?

A

The ions in the solid are attracted ti the polar water molecules breaking the lattice apart

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13
Q

What is the electrical conductivity in a solid for ionic compounds and why?

A

They are poor conductors, due to ions being in a fixed lattice structure and unable to move

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14
Q

What is the electrical conductivity in a aqueous or molten for ionic compounds and why?

A

They are good conductors due to the fact that the ions move

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15
Q

What is a covalent bond?

A

The (strong) electrostatic attraction between a shared pair of electrons and the nuclei of the two bonded atoms

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16
Q

How are covalent bonds formed?

A

When two non-metals atom combine, they share electrons to produce the noble gas configuration of 8 electrons (full octet).
Non-metals can be from the same element

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17
Q

What is the Electron Pair Repulsion Theory (ERPT)?

A

The shapes of molecules are determined by the number of electron pairs surrounding the central atom and whether they are bonding pairs of lone pairs of electrons.

As electron pairs are negatively charged, they repel each other and take up a position so they are as far apart as possible.

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18
Q

What is the first step of determining the shape of from ERPT?

A

Identify the group number of the central atom, this gives the number of electrons in the outer shell of the atom before any covalent bonds form

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19
Q

What is the second step of determining the shape of from ERPT?

A

Add one electron for each covalent bond/atom attached to the central atom

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20
Q

What is the third step of determining the shape of from ERPT?

A

Add or remove electron(s) if the particle is an ion (for example: add one for a single negative ion

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21
Q

What is the fourth step of determining the shape of from ERPT?

A

Work out the total number of pairs of electrons around the central atom.
Work out how many of these are bond pairs and how many are lone pairs

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22
Q

What is the fifth step of determining the shape of from ERPT?

A

Each pair of electrons repels the other pairs as far apart as possible. The name of the shape and bond angle(s) depends on the number of bonding pairs and lone pairs of electrons.

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23
Q

What happens to the non-bonding electrons (lone pairs) in terms of repulsive force?

A

They are closer to the central atom, they have stronger repulsive force so force the bonding pairs closer together

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24
Q

What is the steric number?

A

the total number of atoms directly bonded to a central metal atom and the number of lone pairs attached

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25
Q

Who introduced the concept of electronegativity?

A

Linus Pauling in 1932

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26
Q

What is electronegativity?

A

The ability of an atom to attract (the bonding) electrons towards itself in a covalent bond

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27
Q

What is the trend of electronegativity?

A

Electronegativity increases across a period and decreases down a group.

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28
Q

What are the three most electronegative elements?

A

Nitrogen, oxygen and fluorine

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29
Q

How does electronegativity vary?

A

On the Pauling scale, fluorine is assigned an electronegativity of 3.98, and the other elements are scaled relative to that value

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30
Q

Why does electronegativity increase across a period?

A
  • the number of protons in the nucleus increase
  • electrons are in the same shell
  • greater nuclear attraction for the shared pair of electrons
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31
Q

Why does electronegativity decrease down a group?

A
  • more shells so more shielding
  • although there are more protons this is outweighed by the increased shielding
  • weaker nuclear attraction for the shared pair of electrons
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32
Q

What are non-polar bonds?

A

Where two atoms are joined with a covalent bond, that have the same or very similar electronegativity

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33
Q

How are the electrons in a covalent bond shared (non-polar bonds)?

A

Equally

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34
Q

Where do the pair of electrons sit in a covalent bond (non-polar bonds)?

A

Midway between the two atoms

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35
Q

What are polar bonds?

A

Where two atoms are joined with a covalent bond, they have different electronegativity

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36
Q

How are the electrons in a covalent bond shared (polar bonds)?

A

Unequally

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37
Q

Where do the pair of electrons sit in a covalent bond (polar bonds)?

A

the pair is closer to the more electronegative atom in the covalent bond.
The bond is becoming more like an ionic bond, as there are partial charges on the atoms.

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38
Q

What does bond polarity lead to?

A

Changes in the properties of the molecules, both making the molecules more reactive and altering the physical properties, due to changes in the interactions between the molecules.

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39
Q

what do the delta signs mean? (δ)

A

partial negative or positive charge

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40
Q

What are intermolecular forces?

A

Forces of attraction between molecules
ONLY occur in simple molecules

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41
Q

What does intermolecular forces affect?

A

physical properties of substances - boiling point, melting point, density

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42
Q

What are intermolecular forces of attraction strength compared to ionic, covalent and metallic bonds?

A

weak

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43
Q

What are the three type of intermolecular forces?

A
  • London forces
  • permanent dipole-dipole forces
  • hydrogen bonding
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44
Q

What are London forces?
How strong are they?

A
  • Induced dipole-dipole forces
  • weaker intermolecular force
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45
Q

How London forces form?

A
  • at any moment. the electrons in an atom/molecule are unevenly distributed
  • this creates a temporary dipole
  • this induces an induced dipole in the neighbouring atom/molecule
  • the two dipoles attract each other - London forces of attraction
46
Q

Are London Forces temporary or permanent?

A

Temporary - they are only present for an instant and then the dipole disappears, so attraction between the molecule is very weak

47
Q

Which molecules have Intermolecular London forces?

A

present between all molecules but they are the only force present between non-polar molecules

48
Q

What are non-polar molecules?

A

diatomic and hydrocarbons

49
Q

What happens to the strength of the London forces as the molecule size increases, why?

A

The strength increases, because there are more electrons present so greater uneven distribution of electrons

50
Q

How are permanent dipole - dipole interactions formed?

A

Between bonding atoms that have a significant difference in electronegativity

51
Q

When do permanent dipole - dipole interactions take place?

A

Between molecules which have an overall permanent dipole

52
Q

What is the bond for permanent dipole - dipole interactions in simple molecules?

A

Polar

53
Q

What happens in more complicated molecules in terms of permanent dipole - dipole interactions, what must they contain?

A
  • polar bonds
  • dipoles must be unsymmetrical so they do not cancel.
54
Q

What is the strongest intermolecular force?

A

Hydrogen bonding

55
Q

What is hydrogen bonding?

A

The attraction between a lone pair on a highly electronegative atom in one molecule and a hydrogen atom which is attached directly to a highly electronegative atom in another molecule

56
Q

What is the difference in strength between hydrogen bonds and covalent bonds?

A

Hydrogen bonds are only 10% of the strength of covalent bonds (intramolecular force)

57
Q

What is the effect of hydrogen bonding in water?
- melting/boiling points
- density
- surface tension

A
  • Higher than expecting melting and boiling points
  • ice has a lower density than liquid water
  • water has a high surface tension
58
Q

why does hydrogen bonding in water effected melting/boiling points?

A

because the intermolecular forces in water are strong hydrogen bonds, large energy needed to break

59
Q

Why does hydrogen bonding in water cause a lower density for ice than liquid water?

A

because hydrogen bonds get longer as open lattice structure of ice forms
pushes molecules further apart

60
Q

why does hydrogen bonding in water cause water to have a high surface tension?

A

Due to relatively strong hydrogen bonds between water molecules at the surface of the liquid

61
Q

What is a Dative Covalent bond?

A

the sharing of a pair of electrons between two atoms, where both electrons are provided by the same atom.

62
Q

How is a dative covalent bond shown?

A

as an arrow, showing the direction from where the electrons came from to where they are going

63
Q

What is an adduct?

A

A product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components

64
Q

What should you call bonding instead of just simply ionic or covalent

A

‘predominantly covalent’ or ‘predominantly ionic’

65
Q

What happens when a molecule has a polar bond (covalent)?

A

gives it an ionic character

66
Q

What happens when a molecule has a polar bond (ionic)?

A

gives them a covalent character

67
Q

How can electronegativity values be used for?

A

to give an approximate idea of the predominant type of bonding in a binary compound

68
Q

What does it mean when the electronegativity has a greater difference?

A

the character is more ionic

69
Q

What does it mean when the electronegativity has a smaller difference?

A

the character is more covalent

70
Q

What happens when an ionic bond forms and the cation is very small and highly charged?

A

it will have a high charge density, which will distort the electron cloud of the anion and pull the electrons back towards itself

71
Q

What are the two structures that elements and compounds with covalent bonds could have?

A
  • a simple molecular lattice (simple structure with covalent bonds)
  • a giant covalent lattice (a giant structure with covalent bonding)
72
Q

What is a simple molecular lattice?

A

A three dimensional structure of molecules held together by weak intermolecular forces.

73
Q

What are examples of simple covalent (molecular) structures

A
  • neon
  • nitrogen
  • ice
  • iodine
74
Q

How are simple molecular structures held together?

A

weak intermolecular forces, the atoms within each molecule are bonded covalently

75
Q

What are the changes that take place when iodine change state?

A
  • the weak intermolecular forces between molecules will break
  • the strong covalent bonds between atoms are unaffected
76
Q

What are the physical properties of simple molecular lattices?
- mpt/bpt
- electrical conductivity
- solubility

A
  • low mpt/bpt
  • non-conductors
  • soluble in non-polar solvents
77
Q

why do simple molecular lattices have a low melting and boiling point?

A

the intermolecular forces are weak induced dipole - dipole (London forces) so little energy is needed to break

78
Q

Why are simple molecular lattices non-conductors?

A

because there are no mobile delocalised electrons or ions. (no mobile charged particles)

79
Q

Why are simple molecular lattices soluble in non-polar solvents?

A

as induced dipole - dipole intermolecular forces of attraction will form between the structure and the solvent

80
Q

What is a giant covalent lattice?

A

A three dimensional structure of regularly arranged atoms, all bonded together by strong covalent bonds

81
Q

What examples are there of giant covalent structures?

A
  • diamonds (very hard)
  • graphite (soft)
  • graphene (single layer of graphite only one atom thick)
  • si (similar to diamond)
  • SiO₂ (sand)
82
Q

What are the properties of giant covalent structures?

A
  • high melting points
  • non conductors of electricity
  • insoluble in all solvents
83
Q

Why do giant covalent structures have high melting points?

A

because all atoms are held together by strong covalent bonds which require lots of energy to break

84
Q

Why are giant covalent structures non-conductors of electricity?

A

because all electrons are localised in bonds, there are no delocalised electrons

85
Q

Why are giant covalent structures insoluble in all solvents?

A

because each atom is bonded to every other atom by strong covalent bonds. Atoms cannot interact with solvent molecules

86
Q

What giant covalent structure is an exception to conducting electricity and why?

A

Graphite - each carbon has 1 electron which is delocalised and can move to carry the charge

87
Q

What is a metallic bond?

A

The electrostatic attraction between positively charged cations and the sea of delocalised electrons

88
Q

How does metallic bonding occur?

A

They bond by releasing their outer electrons into a delocalised sea which holds the lattice of cations together due to an attraction of opposite charges.

89
Q

What are the characteristics of metal?

A
  • good conductors of electrons (due to the mobile delocalised electrons moving through the lattice)
  • high melting and boiling point (due to strong electrostatic attraction between positively charged cations and the sea of delocalised electrons, lots of energy needed)
90
Q

What are the exceptions to the dot and cross diagrams (less than 8 electrons)?

A

Berilium, Boron and Aluminium

91
Q

What are the exceptions to the dot and cross diagrams (more than 8 electrons)?

A

Phosphorus and Sillicon

92
Q

What is the name of the molecule shapes with 2 electron pairs and no lone pair?

A

Linear

93
Q

How do you draw a linear molecule shape?

A
94
Q

What is the name of the molecule shapes with 3 electron pairs and no lone pair?

A

Trigonal Planar

95
Q

How do you draw a trigonal planar molecule shape?

A
96
Q

What is the name of the molecule shapes with 4 electron pairs and no lone pair?

A

Tetrahedral

97
Q

How do you draw a tetrahedral molecule shape?

A
98
Q

What is the name of the molecule shapes with 4 electron pairs and 1 lone pair?

A

Pyramidal

99
Q

How do you draw a pyramidal molecule shape?

A
100
Q

What is the name of the molecule shapes with 4 electron pairs and 2 lone pairs?

A

Non-linear

101
Q

How do you draw a non-linear molecule shape?

A
102
Q

What is the name of the molecule shapes with 5 electron pairs and no lone pairs?

A

Trigonal bipyramid

103
Q

How do you draw a trigonal bipyramid shape molecule?

A
104
Q

What is the name of the molecule shapes with 6 electron pairs and no lone pair?

A

Octahedral

105
Q

How do you draw the octahedral shape molecule?

A
106
Q

What is the name of the molecule shapes with 6 electron pairs and 2 lone pairs?

A

Square planar

107
Q

How do you draw the molecule for square planar shape?

A

with 90 degree angles

108
Q

What makes ice have anomalous properties?

A

Ice floats on liquid water due to it being less dense than water. This is because hydrogen molecules hold the structure apart. This creates an open lattice structure.

  • Also has a high and low melting point
109
Q

Steps to tell if a molecule is polar or non-polar?

A
  • dot and cross diagram to work out the shape
  • atoms of significantly different electronegativity?
  • permanent dipoles within the molecule?
  • Using shape will the ‘dipoles cancel’ due to symmetry
  • if they cancel = non-polar
110
Q

What molecules are most likely to form a polar bond?

A

N, O, F, Cl, Br

Chemistry (8 decks)

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