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Chemistry (Tara) > Atomic theory 9 > Flashcards

Atomic theory 9 Flashcards

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1
Q

Define covalent bonding - Intramolecular

A

Covalent bonding occurs when electrons are shared between atoms. Atoms share to attain eight electrons in the outer shell (usually). This type of bonding normally occurs between non-metal atoms.

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2
Q

Are electrons normally localised or delocalised?

A

Localised

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3
Q

What does localised mean?

A

It means that they are not free to move from one atom to the next, but are held between the two atoms.

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4
Q

Single covalent bond e.g HCl

A 
H + CL = HCl
Cl: 3.16
H: 2.20
3.16 - 2.2 = 0.96 = Polar covalent
Cl = S- (higher E.D), H = S+
Single (only sharing 1) polar covalent bond
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5
Q

Double covalent bond e.g O₂

A

O + O = OO = O₂
O: 3.44 - 3.44 = O = Pure covalent
Equal sharing, double pure covalent bond, there is a temporary separation of charge
S-/S+ changes every second

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6
Q

Triple covalent bond e.g N₂

A 
N + N = NN = N₂
N: 3.04 - 3.04 = 0 = Pure covalent
Triple pure covalent bond 
S-/S+ = Changes every second
Note : The high energy triple bond between nitrogen atoms in a molecule of nitrogen makes the gas unreactive
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7
Q

When covalent bonding occurs it involves the ………… of orbitals.

A

Overlapping

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8
Q

Define sigma bonding

A

When orbitals overlap ‘head-on’. This can occur between two S orbitals, an ‘s’ and a ‘p’ orbital or two ‘p’ orbitals. (To get full marks draw a diagram from notes)

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9
Q

Define pi bonding

A

When orbitals overlap ‘side-ways’. This can occur between two ‘p’ orbitals only. (To get full marks draw diagram from notes)

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10
Q

(!!) Sigma bonds always form …….. pi bonds

A

Before

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11
Q

HCl is a….

A

Single sigma polar covalent bond

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12
Q

Why does HCl form a sigma bond?

A

Because the electron in the 1s orbital of H will overlap with the electron in the 3pz orbital of Cl. As they are overlapping ‘head-on’ the we form a sigma bond.

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13
Q

Cl₂ is a….

A

Single sigma pure covalent bond

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14
Q

Why does Cl₂ form a sigma bond?

A

Each Cl atom will share the electron in the 3pz orbital, resulting in a ‘head-on’ overlap, thus the formation of a sigma bond.

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15
Q

All …….. bonds are sigma bonds

A

Single

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16
Q

Check notes at the end of pg 3

A
  1. Not done

5. Done and understood

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17
Q

All double bonds =

A

Sigma and a pi bond

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18
Q

All triple bonds =

A

Sigma and two pi bonds

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19
Q

Why are sigma bonds stronger than pi bonds?

A

As there is more overlapping in a sigma bond.

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20
Q

What does the degree of sharing dependant on?

A

The degree of sharing is dependant on the attraction of an atom for electrons.

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21
Q

What do you get if the atoms have the same attraction for the electrons?

A

A pure covalent bond

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22
Q

What do you get if the atom’s attractions differ?

A

A polar covalent bond

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23
Q

Define pure covalent bonding

A

A pure covalent bond occurs when electrons are shared equally BETWEEN atoms.

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24
Q

Why do both atoms of H form a pure covalent bond?

A

Both atoms of H want to share one electron and as both atoms of H have the same attraction towards these electrons the bond that is formed is a pure covalent bond as the electrons are shared equally between the two atoms.

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25
Q

Check the end of page 5 notes

A

Checked

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26
Q

Define polar covalent bond

A

A polar covalent bond occurs when electrons are shared unequally between atoms.

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27
Q

Name 4 properties of covalent compounds.

A
  1. Usually gases or liquids at r.t
  2. Pure covalent compounds do not conduct electricity.
  3. Generally insoluble in polar water.
  4. Low melting and boiling points.
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28
Q

Why are covalent compounds usually gases or liquids at room temperature?

A

Due to weaker intermolecular forces of attraction between molecules when compared to ion compounds.

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29
Q

Why do pure covalent compounds not conduct electricity?

A

As there are no ions

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30
Q

Why can some polar covalent compounds conduct electricity?

A

Due to the slight charges

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31
Q

Why do covalent compounds have low melting and boiling points?

A

Due to the very weak intermolecular forces of attraction as very little energy is needed to break these factors.

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32
Q

What is ammonia at room temperature?

A

Gas

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33
Q

Why is ammonia a gas at room temperature?

A

Due to weaker Van Der Waals forces

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34
Q

What are the 3 most electronegative elements?

A

F, N and O

35
Q

What type dipole and intermolecular forces does ionic bonding have?

A
  • Permanent dipole

- Ionic attractions

36
Q

What type dipole and intermolecular forces do pure covalent bonds have?

A
  • Temporary dipole

- Van der Waals forces

37
Q

What type dipole and intermolecular forces do polar covalent bonds have?

A
  • Permanent dipole

- Dipole-dipole attractions

38
Q

What type dipole and intermolecular forces do water, ammonia and hydrogen fluoride have?

A
  • Permanent dipole

- Hydrogen bonding

39
Q

What happens in dative covalent bonding?

A

One atom gives both the electrons to the bond.

40
Q

Define polar molecule

A

This term means that the slight positive and slight negative poles of a molecule are separated by a distance. (= do not coincide)

41
Q

Are all molecules with polar bonds polar molecules?

A

No

42
Q

What are pi bonds characterised by?

A
  • Side to die overlap.

- Electron density above and below the intermolecular axes.

43
Q

What is the formation of a sigma bond due to?

A

(a) the s - s overlap
(b) the s - p overlap
(c) the p(z) - p(z) overlap

44
Q

How many types of covalent bonding are there depending on whether the electrons are shared between the atoms equally or unequally?

A

Two

45
Q

What do we get if the atoms have the same attraction for electrons?

A

A pure covalent bond.

46
Q

What do we get if the attractions differ?

A

A polar covalent bond.

47
Q

What is covalent bonding an example of?

A

Intra-molecular bonding.

48
Q

Why is covalent bonding an example of intra-molecular bonding?

A

As the bond occurs between atoms within a molecule.

49
Q

Water is a v-shaped molecule. What does this cause?

A

It to be polar

50
Q

What leads to a molecule being polar?

A

Lack of symmetry

51
Q

What type of molecule is ammonia?

A

Polar

52
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

53
Q

Predict the type of bond formed between carbon and chlorine atoms in a CCl₄ molecule (L.C)

A

Polar covalent

54
Q

Why are polar molecules often called dipoles?

A

As there are two poles of opposite charge within the molecule.

55
Q

State and account for the shape of a tetrachloromethane molecule. (L.C)

A
  • Tetrahedral

- Four pairs electrons and no lone pairs

56
Q

Is the bonding in BF₃ ionic?

A

No

57
Q

Why is the bonding in BF₃ not ionic as expected?

A

As the energy needed to remove the three outer electrons in B is too great, so sharing occurs.

58
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

59
Q

Why is there an increase in electronegativity value moving from gallium to germanium in the periodic table? (L.C)

A
  • Nuclear charge increasing

- Atomic radius decreasing

60
Q

Use electron pair repulsion theory to predict the shape of a molecule of boron trifluoride. (L.C)

A
  • Trigonal planar
61
Q

How do you show that a molecule has x bonding?

A

By finding the electronegativity differences.

62
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

63
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

64
Q

How many (i) sigma bonds, (ii) pi bonds, result from sharing of the valence electrons between the atoms in a molecule of nitrogen. (L.C)

A

(i) 1 sigma

(ii) 2 pi

65
Q

Distinguish between intramolecular bonding and intermolecular forces. (L.C)

A

Intramolecular : forces between atoms in molecules

Intermolecular : forces between molecules

66
Q

Explain in terms of intramolecular bonding and intermolecular forces, why the boiling point of hydrogen (20 K) is significantly lower than that of oxygen (90.2 K). (L.C)

A
  • hydrogen smaller

- weaker intermolecular forces

67
Q

Explain in terms of intramolecular bonding and intermolecular forces, why iodine has a very low solubility in water. (L.C)

A
  • Iodine is pure covalent

- Water is a polar solvent

68
Q

Explain in terms of intramolecular bonding and intermolecular forces, why when a charged rod is held close to a thin stream of water flowing from a burette, the stream of water is deflected. (L.C)

A

Charge on rod attracts opposite charge on polar water molecule.

69
Q

Distinguish between sigma (σ) and pi (π) covalent bonding. (L.C)

A

Sigma - When orbitals overlap ‘head-on’. This can occur between two s orbitals, an ‘s’ and a ‘p’ orbital or two ‘p’ orbitals.
Pi - When orbitals overlap ‘side-ways’. This can occur between two ‘p’ orbitals only.

70
Q

Give one reason why electronegativity values exhibit general increase across the second period of the periodic table. (L.C)

A

Increase in nuclear charge / decrease in atomic radius

71
Q

Show that the ammonia molecule has polar covalent bonding. (L.C)

A
  • There is an electronegativity difference between N and H.
  • N with greater attraction
  • H with smaller attraction
72
Q

Describe the processes involved when ammonia dissolves in water. (L.C)

A
  • Hydrogen bonds between slightly negative O of water and H of ammonia and between slightly positive H of water and N of ammonia.
  • Breaking of hydrogen bonds in water
  • Forming of hydrogen bonds between ammonia and water.
73
Q

Distinguish between sigma (σ) and pi (π) covalent bonding. (L.C)

A

Sigma - When orbitals overlap ‘head-on’. This can occur between two s orbitals, an ‘s’ and a ‘p’ orbital or two ‘p’ orbitals.
Pi - When orbitals overlap ‘side-ways’. This can occur between two ‘p’ orbitals only.

74
Q

State two factors that cause electronegativity values to increase across a period in the periodic table of the elements. (L.C)

A
  • Increasing effective nuclear charge

- Decreasing atomic radius

75
Q

State which of the following compounds contain intermolecular hydrogen bonds, HCl, H₂O, NH₃. Justify your answer. (L.C)

A

H₂O and NH₃

- Hydrogen bonded to a small highly electronegative element (bonded to F, O or N)

76
Q

Suggest a reason why the boiling point of ammonia (-33°C) is significantly lower than that of water (100 °C) (L.C)

A
  • Weaker hydrogen bonding in ammonia

- Stronger hydrogen bonding in water

77
Q

Explain the term intermolecular forces (L.C)

A

Attractive forces(repulsive) between molecules

78
Q

A thin stream of liquid is flowing from the burette. A stream of water is deflected towards a positively charged rod whereas a stream of cyclohexane is undeflected. Account for these observations. (L.C)

A
  • Polarity of water causes attraction to charged rod

- Non-polarity of cyclohexane means it is not affected by charged rod

79
Q

Use electronegativity values to predict the type of bond expected between hydrogen and sulphur. (L.C)

A
  • Weakly polar
  • Almost non-polar
  • Covalent bond
80
Q

Write the chemical formula for hydrogen sulphide. (L.C)

A

H₂S

81
Q

Distinguish between sigma and pi covalent bonding.(L.C)

A

Sigma - When orbitals overlap ‘head-on’. This can occur between two s orbitals, an ‘s’ and a ‘p’ orbital or two ‘p’ orbitals.
Pi - When orbitals overlap ‘side-ways’. This can occur between two ‘p’ orbitals only.

82
Q

Define atomic covalent radius. (L.C) (same as atomic radius)

A

The atomic radius is obtained by getting half the distance between the centres of singly bonded atoms of the same element.

83
Q

Under what circumstances can ionic compounds conduct electricity? (L.C)

A

In water / in the molten state

84
Q

A thin stream of liquid is flowing from the burette. A stream of water is deflected towards a positively charged rod whereas a stream of cyclohexane is undeflected. Explain what would happen in the case of the stream of water if the positively charged rod were replaced by a negatively charged rod. (L.C)

A

Stream of water still attracted to rod as molecules arrange themselves with positive pole towards rod.

Chemistry (Tara) (50 decks)

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