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Chemistry OCR A AS > Module 2.2.2 - Bonding and Structure definitions > Flashcards

Module 2.2.2 - Bonding and Structure definitions Flashcards

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1
Q

What is an ionic bond?

A

The electrostatic attraction between oppositely charged (positively and negatively) ions

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2
Q

What is the octet rule?

A

The tendency to acquire a noble gas electron configuration (8 electrons in its outer shell)

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3
Q

What is covalent bonding?

A

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

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4
Q

What are lone pairs (of electrons)?

A

Pairs of electrons in the outer shell of an atom not involved in covalent bonding

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5
Q

What is a single covalent bond?

A

The sharing of one pair of electrons between two atoms

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6
Q

What are multiple (double/triple) covalent bonds?

A

A double/triple covalent bond is the sharing of two/three pairs of electrons between two atoms

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7
Q

What is dative covalent (coordinate) bonding?

A

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms, where only one of the atoms supplies both of the electrons shared

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8
Q

What is metallic bonding?

A

The **strong electrostatic attraction ** of a lattice of cations (positive metal ions) to a ‘sea’ of delocalised electrons.

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9
Q

What does the giant ionic lattice result from?

A

The regular arrangement of oppositely charged ions strongly attracted in all directions

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10
Q

What do substances need in order to conduct electricity?

A

Mobile charge carrier such as delocalised electrons or mobile ions

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11
Q

What does ‘mobile’ mean

A

Free to move

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12
Q

What is average bond enthalpy?

A

Average bond enthalpy can be used as a measurement of covalent bond strength

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13
Q

What is the basis of electron pair repulsion theory?

A
  • Electron pairs repel each other to get as far away as possible
  • Lone pairs repel more strongly than bonding pairs
  • Shape is determined by the number and type of electron pairs (bond pairs / lone pairs) around the central atom
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14
Q

What does a normal line in a 3D shape represent?

A

Shows a bond in the plane of paper

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15
Q

What does a bold wedge in a 3D shape represent?

A

Bond comes out from the plane of the paper towards you

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16
Q

What does a dashed line/dotted wedge in a 3D shape represent?

A

Bond going out from the plane of the paper away from you

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17
Q

What is a linear molecule?

A
  • 2 bonded pairs, 0 lone pairs
  • bond angle 180°
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18
Q

What is a trigonal planar molecule?

A
  • 3 bonded pairs, 0 lone pairs
  • bond angle of 120°
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19
Q

What is a tetrahedral molecule?

A
  • 4 bonded pairs, 0 lone pairs
  • bond angle of 109.5°
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20
Q

What is a octahedral molecule?

A
  • 6 bonded pairs, 0 lone pairs
  • bond angle of 90°
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21
Q

What is a pyramidal molecule?

A
  • 3 bonded pairs, 1 lone pair
  • bond angle of 107° (109.5°-2.5°)
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22
Q

What are the non-linear molecules?

A
  • 2 bonded pairs, 1 lone pair
  • bond angle of 117.5° (120°- 2.5°)
    OR
  • 2 bonded pairs, 2 lone pairs
  • bond angle of 104.5° (109.5°- 5°)
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23
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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24
Q

What are non-polar bonds?

A

The difference in electronegativity is 0, bonded electrons are equally distributed

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25
Q

When do non-polar bonds occur?

A

Where the bonding atoms are the same such as H-H and Cl-Cl

26
Q

What are polar covalent bonds?

A

Where there is a medium to small difference in electronegativity between the bonded atoms

27
Q

What happens between the bonded atoms in a polar covalent bond?

A

There is a permanent dipole across the bond due to the small difference in charge across the bond

28
Q

What happens to the shared electrons in a polar covalent bond?

A

Bonding electrons are attracted closer to the more electronegative atom , electron cloud is more dense

29
Q

What is the general trend for electronegativity in the periodic table?

A

Electronegativity increases towards the top right of the periodic table (halogens, excluding most noble gases)

30
Q

The greater the difference in electronegativity between the bonded atoms…

A

the greater the permanent dipole and the more polar the covalent bond.

31
Q

What do polar covalent bonds have in terms of charges?

A

Slight/Partial charges, represented with a dipole

32
Q

Why do carbon and hydrogen not form a polar covalent bond?

A

There is a very small difference in electronegativity between C and H

33
Q

Why are symmetrical molecules non-polar?

A

The dipoles cancel out between each polar bond, hence no net dipole across the molecule

34
Q

When are asymmetrical molecules polar?

A

When they contain one or more polar bonds

35
Q

How can you tell is a molecule is asymmetric?

A
  • has lone pairs
  • surrounding atoms are not all the same
36
Q

Why are asymmetrical molecules polar?

A

The dipoles do not cancel out

37
Q

What are intermolecular forces?

A

Attractive forces between molecules which are much weaker than ionic or covalent bonds

38
Q

What structures have intermolecular forces?

A

Covalent structures

39
Q

What are induced dipole-dipole interactions?

A

Very weak intermolecular forces between molecules

40
Q

What are other names for induced dipole-dipole interactions?

A
  • London forces
  • Dispersion forces
41
Q

Where do induced dipole-dipole interactions exist?

A

Between all molecules, whether polar or non-polar

42
Q

How do induced dipole-dipole arise between molecules?

A
  • At any moment there may be an uneven distribution of electrons in a molecule, due to electron movement/change in electron density
  • This causes a temporary dipole/instantaneous dipole to occur
  • The instantaneous/temporary dipole in one molecule causes an induced dipole in a neighbouring molecule
  • The slightly positive charge of a dipole in one molecule attracts the slightly negative charge of a dipole in a neighbouring molecule, producing a induced dipole-dipole attraction
43
Q

What are permanent dipole-dipole interactions?

A

Weak attractive forces between polar molecules

44
Q

How do permanent dipole-dipole interactions occur?

A
  • A molecule has bonds that are permanently polar as one atom is more electronegative than the other and is asymmetrical so the dipoles do not cancel each other out
  • the slightly positive dipole of one molecule attracts the slightly negative dipole of a neighbouring molecule to produce the permanent dipole-dipole force of attraction between the molecules
45
Q

What can both permanent dipole-dipole interactions and induced dipole-dipole interactions be referred as?

A

Van der Waals forces

46
Q

What are hydrogen bonds?

A

A strong dipole-dipole attraction between molecules containing O-H, N-H or F-H bonds, the strongest type of intermolecular force of attraction

47
Q

What does the hydrogen bond exist between?

A
  • The slightly positive charge on the hydrogen in one molecule
  • a lone pair on a highly electronegative atom (O, N, F) on another molecule
48
Q

How do you draw a hydrogen bond? [3 marks]

A
  • labelled atoms (with dipoles)
  • lone pairs of electrons
  • dotted line (hydrogen bond)
49
Q

Why does water have anomalous properties of water?

A

Due to the hydrogen bonds between water molecules

50
Q

Why is ice (solid H2O) less dense than liquid water?

A
  • In the solid, H2O molecules are held further apart by the hydrogen bonds
  • This gives the ice an open lattice structure
  • The H2O molecules are fixed in their positions in the 3D ice crystal lattice by hydrogen bonds
51
Q

Why does water have relatively high melting and boiling points?

A
  • Water has higher than expected melting and boiling points
  • Hydrogen bonds are relatively strong, therefore stronger than other intermolecular forces
  • more energy is needed to break the hydrogen bonds
52
Q

What does melting and boiling points depend on?

A

The structure and the strength of the bonds, which need to be overcome and broken

53
Q

When does a substance have a high melting/boiling point?

A

The bonds broken are strong

54
Q

What is the structure of substances with a high melting/boiling point?

A

Giant

55
Q

When does a substance have a low melting or boiling point?

A

When the bonds broken are weak

56
Q

What is the structure of substances with a low melting/boiling point?

A

Simple

57
Q

When is there a sharp decrease in melting and boiling points across a period?

A

Between group 4 and 5

58
Q

What does the decrease show across the period?

A

The change from giant structures to simple structures

59
Q

What are the bonds that need to be broken in substances with a high melting or boiling point?

A

Strong bonds between the particles/atoms

60
Q

What are the bonds that need to be broken in substances with a low melting or boiling point?

A

Weak intermolecular forces between molecules

61
Q

What happens to the melting or boiling point across a period from group 1 to group 4?

A

Increase gradually

62
Q

What are relative to the melting or boiling points across a period from group 5 to group 8?

A

They are comparatively low

Chemistry OCR A AS (27 decks)

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