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Chemistry > Topic 4: Bonding > Flashcards

Topic 4: Bonding Flashcards

1
Q

Describe structure of an ionic compound

A
  • Giant ionic lattice

- Electrostatic forces of attraction between oppositely charged ions

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2
Q

Describe ionic bonding

A
  • Occurs between a metal and a non-metal
  • When electronegativity difference is high between atoms, electrons are transferred from the metal to non-metal
  • forms ions
  • electrostatic forces of attraction between oppositely charged ions
  • in a GIANT IONIC LATTICE structure
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3
Q

Why are some molecules polar?

A
  • Polar bonds
  • Asymmetrical distribution of charge
  • dipoles do not cancel
  • hence net dipole moment
  • draw arrow on lewis structure
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4
Q

Describe covalent bonding

A

A covalent bond is formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei.

Occurs between NON METALS only

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5
Q

Describe metallic bonding

A

Electrostatic forces of attraction between a lattice of positive ions and the surrounding sea of delocalized electrons

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6
Q

Why are ionic compounds/metals brittle?

A
  • Ionic compounds are brittle because slight movement brings ions of same charge adjacent to each other
  • Repulsion between layers.
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7
Q

Why do metals have low electronegativites

A

They need to lose electrons to form an octet

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8
Q

VSEPR full name and what does it suggest?

A

Valence shell electron pair repulsion - non-bonding pairs of electrons repel each other more

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9
Q

Describe possible molecular geometries for tetrahedral electron domain?

A

Tetrahedral (109.5)
Trigonal pyramidal (107)
Bent (104.5)

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10
Q

Describe possible molecular geometries for trigonal planar electron domain

A 
Trigonal planar (120)
Bent (117.5)
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11
Q

Describe possible molecular geometries for trigonal bipyramidal

A

Trigonal bipyramidal (90,120)
Seesaw (90 <120)
T-Shaped (90, 180)
bent (90, <180)

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12
Q

How to determine whether molecules are polar or non-polar?

A

They are polar if:

  • lewis structure has lone pairs on central atom (unless it is a molecule like XeCl2 which has 3 lone pairs on central atom so it would be non-polar)
  • different atoms bonding to central atom rather than just one e.g: CCl4
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13
Q

How to calculate bond order?

A

Total number of bonding pairs/total number of positions double bond can be in

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14
Q

Co-ordinate covalent bond

A

The electrons in the shared pair may originate from the same atom.

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15
Q

Order single, double and triple bonds in terms of strength and length (from least to most)

A

Length:
triple, double, single

Strength:
single, double, triple

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16
Q

Describe trend in group 6 hydrides

A

H2O has high MP due to hydrogen bonding which is stronger than Van der Waals.

Increase in Mr means increase in electrons, more electron distortion, so more Van der Waals

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17
Q

Why are some molecules soluble in water

A
  • They can form hydrogen bonds with water
  • as they are polar
  • negative dipole attracts positive dipole of water and vice versa
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18
Q

Explain what ‘like dissolves like’ means

A

Polar compounds soluble in polar substances and non polar soluble in non polar substances

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19
Q

Describe possible molecular geometries for octahedral electron domain

A 
Octahedral (90)
Square pyramidal (<90)
Square planar (90)
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20
Q

Describe benefits of ozone

A

Absorbs UV light emitted from sun, protects from skin cancer

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21
Q

Why does water have a maximum density at 4 degrees celcius rather than when it is ice

A
  • Hydrogen bonding between water molecules
  • Each water bonds to 4 other water molecules
  • Very open tetrahedral structure
  • When it melts, molecules move closer to each other
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22
Q

Describe the characteristics of diamond as an allotrope of carbon

A
  • Strong covalent bonds
  • Each carbon atom bonds to 4 other carbon atoms
  • Tetrahedral structure
  • Giant covalent
  • Hard
  • No delocalised electrons so not a conductor of electricity
  • used as a cutting tool
  • Sp3 hybridisation, 109.5 bond angle
  • insulator
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23
Q

Describe graphite

A
  • Giant covalent
  • Each carbon bonded to 3 other carbon atoms
  • delocalised electrons so conducts electricity
  • Weak intermolecular forces between layers
  • Layers can slide over each other due to weak London Dispersion Forces
  • lubricant
  • 120 degrees
  • sp2
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24
Q

Describe graphite

A
  • Giant covalent
  • Each carbon bonded to 3 other carbon atoms
  • delocalised electrons so conducts electricity
  • Weak intermolecular forces between layers
  • Layers can slide over each other
  • lubricant
  • sp2
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25
Q

Graphene

A
  • Single layer of gaphite
  • Simple covalent
  • Each carbon bonded to three others
  • delocalised electrons, so conducts electricity
  • sp2
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26
Q

Fullerene

A
  • 60 carbon atoms
  • arranged in hexagons and pentagons
  • forms a spherical shape
  • Poor electrical conductor
  • each carbon bonded to 3 others
  • sp2
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27
Q

EXAM TIPS

A
  • Some molecules have non-polar covalent bonds due to low E.M difference but are still polar molecules overall because of their geometry (e.g: lone pairs on central atom) such as ozone, as well as PH3 which has non-polar covalent bonds but is a polar molecule overall due to lone pairs however if there is no lone pair and only non-polar covalent bonds then molecule can’t be polar

The whole point of a polar molecule is an uneven charge distribution

  • remember to draw lone pairs on lewis structures, don’t rush it
  • when doing ozone wavelength calculations, remember to first MULTIPLY BY 1000 and then DIVIDE BY 6.02 X 1023. Then at the end once calculator gives you the value, MULTIPLY BY 10^9 TO CONVERT INTO NM
  • If it asks to find hybridisation in a given lewis structure for numbered atoms, REMEMBER LONE PAIRS MAY EXIST THAT HAVN’T BEEN DRAWN ON sneakily. Lone pairs do influence hybridisation to remember to take them into account
  • You’ll do amazing. You’ve got this. Keep revising.
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28
Q

Hydridization

A

sp, linear, 180
sp2, trigonal planar, 120
sp3, tetrahedral, 109.5

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29
Q

Ozone calculation:

A 
Wavelength = HC/E
h = plank's constant
c = speed of light
E = energy - calculated using data booklet.

The energy is the bond enthalpy which is on page 11 in data bk. Draw lewis structure of molecule they want to see if it is a single/double/triple bond between the 2 atoms and find enthalpy accordingly.

Multiply this value by 1000, then divide by 6.02 x 1023 for 1 bond. This is the E value which you can substitute into the equation to find the wavelength

ONCE WAVELENGTH FOUND, multiply by 10^9 to convert it into nanometres. This will be the final answer.

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30
Q

What is hybridisation?

A

Mixing of atomic orbitals to form molecular orbitals of degenerate energy

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31
Q

Describe Sp3 hybridisation

A

1 electron from 2s orbital goes into empty 2p orbital. The 4 orbitals mix together to form 4 degenerate sp3 orbitals. These form sigma bonds only because no unhybridised p-orbitals are left

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32
Q

Describe formation of a sigma bond

A

Axial, head on head overlap of orbitals trapping electron density between nuclei of atoms. Forms between an s and an s, p and a p, or s and a p orbital

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33
Q

Describe formation of a pi bond

A

Sideways overlap of unhybridised p orbitals, trapping electron density above and below internuclear axis

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34
Q

Describe sp2 hybridisation

A

1 electron from 2s orbital enters empty 2p orbital.

2 p orbitals and the 2s orbitals mix together, forming 3 sp2 orbitals

1 unhybridised p orbital left

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35
Q

Discuss the bonding in the resonance structures of ozone.

A

one pair on p orbital of O atom overlaps/delocalizes with pi electrons from double bond

both O–O bonds have equal bond length

both O–O bonds have same/1.5 bond order

both O–O are intermediate between O–O AND O=O

both O–O bonds have equal bond energy

Pi electrons are delocalized

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36
Q

Describe, by means of equations, how nitrogen(II) oxide, NO, catalyses the depletion of ozone.

A

NO (g) + O3 (g) -> NO2 (g) + O2(g)

NO2(g) -> NO(g) + O. (g)

NO2(g) + O. (g) -> NO(g) + O2

NO2 + O3 -> NO + 2O2

O3 + O. -> 2O2

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37
Q

State the source of ozone depleting pollutants

A 
Nitrogen dioxide
CFCs
propellants in aerosol cans
air conditioners
fire extinguishers
solvents
plastic foams
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38
Q

Explain how the bonding in O2 and O3

affects the wavelengths of UV light they absorb.

A

O2 has a double bond
O3 1.5 bond order
O2 shorter and stronger bond than O3
O2 absorbs shorter wavelength than O3

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39
Q

Bonding in the nitrate ion involves electron delocalization. Explain the meaning of electron delocalization and how it affects the ion

A

pi electrons shared by more than two atoms/nuclei / a pi/
π bond/overlapping p-orbitals that extends over more than two atoms/nuclei;

all (N–O) bonds equal length/strength/bond-order / charge on all oxygen/O atoms equal / increases stability/lowers PE (of the ion);

40
Q

State one environmental problem caused by these atmospheric pollutants

A

Depletion of ozone layer

41
Q

Explain, on a molecular level, why ozone dissociates with radiation of a longer wavelength than oxygen

A

O3 needs less energy/weaker bonding

O3 has bond order 1.5/ intermediate between double and single

42
Q

Nitrogen(II) oxide, NO, is a primary pollutant that depletes the ozone layer. State two equations that show how this oxide catalyses the depletion of ozone in the stratosphere

A

NO∙(g) + O3(g) → NO2∙(g) + O2(g)

NO2∙(g)+O∙(g)→NO∙(g)+O2(g);

43
Q

Discuss one advantage and two disadvantages of using hydrocarbons as alternatives to CFCs

A

Do not damage ozone layer
Decompose less readily than CFCs
Cheaper than CFCs
HOWEVER, both contribute to global warming

44
Q

Why are CFCs expected to remain the atmosphere for many years

A
  • Low reactivity
  • Some countries still producing CFCs
  • Produce radicals
  • slow mixing between troposphere and upper atmosphere
45
Q

Why does PCl5 have a higher MP than PCl3

A
  • stronger Van der Waals forces

- due to more electrons and a greater mass

46
Q

What are the 3 types of intrAmolecular bonding?

A

Ionic
Covalent
Metallic

47
Q

4 types of intermolecular?

A

Hydrogen bonding
Dipole-dipole
Induced dipole
London dispersion forces

48
Q

Which elements form hydrogen bonding and why

A

FON

Most electronegative atoms that’s why

49
Q

Explain an instantaneous dipole

A

An instantaneous dipole is produced due to the random motion of electrons around the nucleus of atoms.

Electrons become asymmetrical around the nucleus of an atom.

When the electrons in nearby atoms come near each other, they induce a dipole in the nearby atom due to repulsion between the electrons, leaving a positive dipole on the nearby atom, attracted to the negative dipole on the atom that induced the dipole.

50
Q

Explain the factors that affect the strength of London dispersion forces

A

Molecules with a larger SURFACE AREA will have a greater likelihood of coming into contact with each other and therefore there will be greater repulsion between the electrons, leading to stronger LDF between molecules.

The greater the SIZE of the molecule, the stronger the LDF because there will be more electrons in a larger molecule. The more electrons, the further they’ll be from the nucleus, less attraction on these so form dipoles more easily

51
Q

Any ion that ends in “ide” means…

A

It gains electrons

52
Q

Carbon ion formula?

A

C4+

53
Q

Carbide ion formula

A

C4-

54
Q

Draw the line which separates metals from non-metals

A

Boron to Te

55
Q

Describe volatility of ionic compounds

A

Ionic compounds have a low volatility because ions are held together in the giant ionic lattice with strong electrostatic forces, no free to move

56
Q

If asked to determine which has a stronger ionic bond, what would you do?

A

Determine charge density by seeing which atoms are larger

Larger atoms will have a smaller charge density

57
Q

Is water dissolving ionic compound exo or endothermic

A

Water attracted to ion and forming bonds with it is EXO

Ion being pulled away from lattice - ENDO because it is bond breaking

58
Q

Polyatomic ions:

A 
NH4 +
OH -
NO 3-
HCO 3- 
CO3 2-, 
SO4 2- 
PO4 3-
59
Q

Polyatomic ions:

A 
NH4 +
OH -
NO 3-
HCO 3- 
CO3 2-, 
SO4 2- 
PO4 3-
HSO4-
60
Q

Why does bond polarity occur?

A

Bond polarity results from the difference in electronegativities of the bonded atoms.

This causes an unequal distribution of charge.

61
Q

What do lewis structures show?

A

Lewis (electron dot) structures show all the valence electrons in a covalently bonded species.

62
Q

What is the octect rule?

A

The “octet rule” refers to the tendency of atoms to gain a valence shell with a total of 8 electrons.

63
Q

Which atoms might form stable compounds with incomplete octets of electrons

A

Some atoms, like Be and B, might form stable compounds with incomplete octets of electrons.

64
Q

Why does resonance occur

A

Resonance structures occur when there is more than one possible position for a double bond in a molecule.

65
Q

Difference between London dispersion and Van der Waals

A

The term “London (dispersion) forces” refers to instantaneous induced dipole- induced dipole forces that exist between any atoms or groups of atoms and should be used for non-polar entities.

The term “van der Waals” is an inclusive term, which includes dipole–dipole, dipole-induced dipole and London (dispersion) forces.

66
Q

Explain the physical properties of covalent compounds (volatility, electrical conductivity and solubility) in terms of their structure and intermolecular forces.

A

Simple covalent molecules have a high volatility due to weak intermolecular forces, e.g: London dispersion and Van der Waals that do not need too much energy to be overcome

Insoluble

Do not conduct electricity because VALENCE electrons are tightly bound in covalent bonds - no free charged particles to move and carry a current

67
Q

Which molecules form dative covalent bonds and which do not

A

NH3
Oh4 - hydronium - both electrons come from oxygen
CO

68
Q

Which 2 elements have greatest difference in electronegativity

A

Francium to Fluorine

69
Q

Describe EN values for polar, non-polar covalent bonds

A

0 - 0.3 = non-polar covalent

  1. 4 - 1.7 = polar covalent
  2. 8 + = ionic
70
Q

How to determine if NaF is ionic or covalent

A

Melt it and see if it conducts electricity.

If it does then it is ionic

If it doesn’t then it is covalent

71
Q

Tetrahedral examples

A

CH4

NH4+

72
Q

3 bonding, 0 lone?

A

Trigonal planar

120 degrees

73
Q

4 bonding, 0 lone?

A

Tetrahedral

109.5

74
Q

2 bonding, 0 lone?

A

Linear

180 degrees

75
Q

2 bonding, 1 lone?

A

Bent

117.5

76
Q

3 bonding, 1 lone?

A

Trigonal pyramidal

107

77
Q

2 bonding, 2 lone

A

Bent

104.5

78
Q

5 bonding, 0 lone

A

Trigonal bipyramidal

90, 120

79
Q

4 bonding, 1 lone

A

Seesaw

90, <120

80
Q

3 bonding, 2 lone

A

T-shaped

<90, <180

81
Q

2 bonding, 3 lone

A

Bent

180

82
Q

6 bonding, 0 lone

A

Octahedral

83
Q

5 bonding, 1 lone

A

Square pyramidal

84
Q

4 bonding, 2 lone

A

Square planar

85
Q

If central atom has 3 lone pairs what shape is it?

A

Linear

180 degrees

86
Q

Bond order formula

A

Bond order = (Number of electrons in bonding molecules) - (Number of electrons in antibonding molecules)]/2

87
Q

Describe structure of silicon + silicon dioxide

A

Macromolecule
Forms 4 bonds
High MP

88
Q

Which covalent compounds are electrical conductors

A

Graphite - delocalised electrons between layers as carbon bonds to only 3 other carbons

NH4NO3 - in solid and gas state, NOT solid

Buckminister fullurene - poor conductor

89
Q

Why are metals malleable

A

Can be bent/re-shaped

Positive ions are rearranged because positive ions repel each other

90
Q

Formal charge equation

A

of valence electrons - (1/2 x bonding electrons + # of lone pair electrons - THIS IS FOR ONE ATOM)

91
Q

Which molecule is the most favoured

A

Closest to 0

92
Q

Calculation of wavelength needed to break ozone Oxygen-Oxygen bond

A

363 KJ mol- x 1000 = 363000 to get into Joules per mol

Divide 363000 by 6.02 x 10^23 = to find for ONE O-O

This is the ENERGY (E) value in the equation E = hv

find velocity

substitute velocity into c = wavelength x velocity

Find wavelength

93
Q

Discuss the depletion of the ozone layer

A

CFC rises up to the ozone layer

High energy UV breaks off Chlorine radical

Chlorine radical breaks off ozone radical

This causes 3 oxygen molecules to be produced

Oxygen does not protect us from UV rays which can cause skin cancer

94
Q

Equation of the CCl2F2 and ozone depletion

A

C Cl2 F2 -> C Cl F2. + Cl.

O3 + Cl. -> O2 + ClO.

ClO. + O. -> O2 + Cl.

95
Q

Overall equation for ozone depletion

A

O. + O3 -> 2O2

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