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Chemistry > Shapes Of Molecules And IMF > Flashcards

Shapes Of Molecules And IMF Flashcards

1
Q

What is a valence shell?

A

The outer shell

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2
Q

What are lone electron pairs?

A

Two electrons that are not involved in a Bond

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3
Q

What is the valence shell electron pair repulsion theory?

A

Pairs of electrons in valence shell repel each other as far as possible

Multiple bonds have same effect as single bonds

Lone pair of electrons have larger repelling effect than bonded electrons (more lone electrons= reduces bond angle)

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4
Q

How do you determine the shape of a molecule and bond angles?

A

Draw dot and cross diagram

Take into account repelling effects of bonds

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5
Q

What is the shape and bond angle of a molecule with 2 bonded pair of electrons/ regions?

A

Linear

180

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6
Q

What is the shape and bond angle of a molecule with 3 bonded pair of electrons/ regions?

A

Trigonal planar

120

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7
Q

What is the shape and bond angle of a molecule with 4 bonded pair of electrons/ regions?

A

Tetrahedral

109.5

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8
Q

What is the shape and bond angle of a molecule with 6 bonded pair of electrons/ regions?

A

Octahedral

90

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9
Q

What is a dative bond?

A

A covalent bond where nth electrons come from the same atom

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10
Q

What does the triangle in a dot and cross diagram signify?

+ when is it used?

A

Used in poly atomic ions

To signify electrons gained

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11
Q

What is a covalent bond?

A

The attraction between the positive nucleus of two atoms and the negative electrons they share .

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12
Q

What is electronegetivity?

A

The ability of an atom to attract the bonded pair of electrons in a covalent

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13
Q

What are the electronegativity values called?

A

Pauling electronegativity values

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14
Q

What is the most electronegative atom?

A

Fluorine

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15
Q

What is a polar bond ?

A

A covalent bond where each atom has different electronegativities with + and - partially charges on the atoms

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16
Q

Will the more electronegative atom has a + or - partial charge?

A

Partial negative charge

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17
Q

What is a dipole?

A

The separation (short distance) of partial charges in a molecule

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18
Q

What is a permanent dipole?

A

The separation of partial charges across a polar bond due to different electronegativities

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19
Q

When is molecule polar?

A

When a molecule has more than one polar bond and is not symmetrical

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20
Q

Why are some molecules non-polar even though they have 2+ polar bonds?

A

The molecule is symmetrical so the dipole acts in opposite directions and cancels out

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21
Q

What are intermolecular forces?

A

Weak attraction between molecules

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22
Q

What are the types of intermolecular forces?

A

Induced dipole-dipole attraction (London forces)

Permanent dipole-dipole interactions

Hydrogen bonding

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23
Q

What are temporary dipoles and why do they form?

A

Dipoles caused by uneven distribution of electrons

Form due to random nature of electron movement

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24
Q

What is an induced dipole and how is it created?

A

A dipole caused by the presence of a temporary dipole in a molecule

Chain reaction

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25
Q

What is a London force?

A

The force of attraction between induced dipoles

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26
Q

Where do London forces occur?

A

In all molecules

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27
Q

What does the head of an arrow indicate in terms of dipoles?

A

Partial negative charge

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28
Q

What causes a stronger London force ?

A

More electrons

29
Q

Why do elements with more electrons have higher MP and BP?

A

More electrons= stronger London forces (occurs in all molecules and is a type of intermolecular force)

More energy needed to break the bonds

30
Q

What is a permanent dipole-dipole interaction?

A

Type of intermolecular force.

Between two polar molecules with permanent dipoles

Attraction is between + and - partial charges

31
Q

What occurs to permanent dipole-dipole interactions in a liquid?

A

They are constantly breaking and reforming (molecules move)

32
Q

What occurs to permanent dipole-dipole interactions in a solid?

A

The interactions are constant so hold molecules in a fixed position

33
Q

What is a hydrogen bond also known as?

A

Very strong permanent dipole-dipole interaction

34
Q

What is a hydrogen bond?

A

Attraction between

hydrogen atom bonded to electronegative atom in one molecule
+
Lone pair of electrons of an electronegative element in a different molecule

35
Q

Give examples of molecules with hydrogen bonding

A

H2O

NH3

HF

36
Q

Why is ice less dense than water?

A

Water molecules are held in open lattice structure in ice (very regular structure) making it less dense.

When it melts the lattice collapses

37
Q

How are molecules in a simple molecular lattice held in place?

A

By weak intermolecular forces

38
Q

Are the MP and BP of simple molecular lattices high or low ?

Why?

A

Low

Weak intermolecular forces are easy to overcome

39
Q

Why are simple molecular lattices poor conductors of electricity?

A

They aren’t charged

40
Q

Are highly polar molecules soluble or insoluble in water?

Why?

A

Soluble

They can interact with the dipoles in water

41
Q

What are simple molecules soluble and insoluble in?

Why?

A

Soluble = non-polar substances

Insoluble= water

Due to weak dipoles

42
Q

What is an instantaneous dipole?

A

A dipole only present for an instant (caused by the accumulation of electrons)

43
Q

What is the name for the electrons involved in a covalent bond?

A

Bonding pair

44
Q

What is the rule for drawing ions?

A

Same as uncharged molecules (based on types and number of bonding regions)

45
Q

What effects electronegativity?

A

Electron shielding

Nuclear charge
Atomic radius

46
Q

How does electronic shielding affect electronegativity?

A

More shells= less electronegative

Inner shell electrons repel outer shell electrons making attraction to nucleus weaker

47
Q

What letter is used to depict a partial charge?

A

Lower case delta

48
Q

What value determines a covalent, polar covalent and ionic bond?

A

Covalent = 0

Polar covalent = 0 >_ 0.18

Ionic = > 1.8

49
Q

In a simple molecular lattice what forces hold the molecules in place?

A

London forces

50
Q

What may occur due to permanent dipole-dipole interaction?

A

The partial charges may increase

Electrons are reopened by partial charge on neighbouring molecule making them move further away from partial positive charge

51
Q

How many hydrogen bonds are there per water molecule in ice?

A

4

52
Q

What are van der Waals forces?

A

Induced dipole-dipole interactions (London forces)

And

Permanent dipole-dipole interactions

53
Q

What does a lone pair reduce the bond angle by?

A

2.5 per lone pair

54
Q

What increases the strength of London forces ?

A

More electrons

Larger SA = bigger exposed electron cloud = greater attraction

55
Q

What are the anomalous properties of water?

A

Higher M+Bp than expected

Ice is less dense than water

56
Q

Explain why ice is less dense than water

A

There are more hydrogen bonds in ice than water (4)

When ice melts some hydrogen bonds break and molecules are closer so it’s more dense

Hydrogen bonds are relatively long and so hold water molecules in an open lattice structure

57
Q

Place the IMF in order of increasing strength

A

Induced dipole-dipole

Permanent dipole-dipole

Hydrogen

58
Q

What is the structure of simple molecules held by London forces

A

Molecular lattice

59
Q

How many bonded and lone pairs does trigonal pyramidal have?

What is the bond angle?

A

Bonded= 3

Lone= 1

Angle =107

60
Q

How many bonded and lone pairs does a molecule with bond angle 104.5 have?

What is it’s name?

A

2 bonding regions (double bonds)

Two lone.

Non-linear

61
Q

What shape of molecule has two bond angles and what are they?

A

Trigonal bipyramidal

90+ 120

62
Q

Are molecules with hydrogen bonding soluble in water?

Why?

A

Yes

Can form hydrogen bonds with water

63
Q

Describe the solubility of polar and non-polar solutes

A

Like dissolves like

64
Q

Will a polar solvent dissolve and non-polar solute?

Why?

A

No

Partial charges aren’t strong enough the separate atoms (break covalent bond)

65
Q

Give pauling En values for pure covalent, polar covalent and ionic bonds

A 
Pure = 0
Polar= up to 1.8
Ionic= 1.8+
66
Q

Define bond in molecules with 0, 0.6 and 2.5 difference in electronegetivity values of atoms

A

0= pure covalent

  1. 6 =polar covalent
  2. 5 =ionic
67
Q

What IMF does water have?

A

London forces
Permanent dipole-dipole
Hydrogen

68
Q

Why does Br2 have a higher boiling point than f2?

A

Br has more electrons so stronger London forces

Chemistry (28 decks)

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