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A HL Chemistry 2024/2025 > Structure 2.2 > Flashcards

Structure 2.2 Flashcards

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1
Q

Retardation factor

A

Distance travelled by component/distance travelled by the solvent from original spot

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2
Q

When do resonance structures occur?

A

When there is more than one possible place for a double bond in a molecule

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3
Q

Covalent bond

A

Sharing of electrons between atoms to form a noble gas electron configuration (known as octet rule) due to electrostatic attraction

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4
Q

Single covalent bond

A

When one pair of electrons is shared between two atoms

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5
Q

Lewis formula

A

Formula that shows all of the outer valence electrons for each atom in the molecule

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6
Q

What happens to the bond length and bond strength when pairs of shared electrons increases?

A

Generally, bond length decreases and bond strength increases as number of shared pairs of electrons increases

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7
Q

Coordinate covalent bond

A

When both electrons are contributed from the same atom

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8
Q

Octet rule

A

Atoms bond together and share electrons to gain a full outer shell

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9
Q

Why don’t noble gases form compounds?

A

They are already stable with a full outer shell.

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10
Q

Most electronegative atom

A

Flourine

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11
Q

Atoms lower in the periodic table… (octet rule)

A

Can defy the octet rule

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12
Q

Electronegativity

A

The relative attraction that an atom has for a shared pair of elections when covalently bonded.

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13
Q

What is electronegativity measured in?

A

Pauling scale

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14
Q

Electronegativity trends…

A

Increase across a period and up a group so N, O, F are most electronegative

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15
Q

A covalent bond between two atoms of the same element will be

A

Non-polar as bonding is shared equally

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16
Q

A covalent bond between two atoms of different elements will be

A

Polar as bonds will be attracted to each other

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17
Q

What happens if the difference between electronegativity is greater than about 1.8?

A

The bonding pair of electrons moves completely towards the more electronegative atom and bonding becomes ionic.

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18
Q

Electron affinity

A

The amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion.

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19
Q

Bond polarity

A

The distribution of electric charge across a chemical bond between two atoms.

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20
Q

Molecular polarity

A

A molecule (or polyatomic ion) is polar when one side of the molecule is more positive (or more negative) than the other

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21
Q

Valence Shell Electron Pair Repulsion

A

States that pairs of electrons are arranged around the central atom i a simple molecule or ion so that they are mutually repulsive

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22
Q

What does the VSEPR theory apply to?

A

Strictly speaking only electron domains but for most purposes, electron pairs

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23
Q

All electrons in a multiple bond must…

A

Point in the same direction

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24
Q

What is the order of repulsion?

A

Non bonding : non bonding > non bonding : bonding > bonding : bonding

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25
Q

To determine whether a molecule is polar or non polar, consider …

A

Both the electronegativities of the bonded atoms and the shape of the molecule

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26
Q

Molecules are polar when

A

Their bond dipoles do not cancel out, bent shape

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27
Q

Molecules are non polar when

A

Their bond dipoles cancel out, when dipoles are equal, linear shape

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28
Q

Covalent network structure

A

Lattice of atoms that are covalently bonded together

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29
Q

Covalent molecules b/m points

A

Are very high

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30
Q

Covalent molecules conductivity

A

Poor conductors as all electrons are localised and so cannot carry charge

31
Q

Allotropes chemical and physical properties

A

Are different as they have different bonding and structural properties

32
Q

Diamond

A

Bonded tetrahedrally to four other carbon atoms, is hardest natural substance

33
Q

Graphite

A

Allotrope of carbon, trigonal planar bonding to three other carbons and so layers held together by weak bonds. Delocalised electrons so good conductor of electricity.

34
Q

Buckminsterfullerence

A

60 carbon atoms, arranged in rings to form a sphere

35
Q

Silicon/silicon dioxide

A

Tetrahedral bonding so no free electrons, hard, high melting point and can’t conduct.

36
Q

Van der Waal’s forces of attraction

A

General term that covers all weak forces of attraction between molecules

37
Q

London dispersion forces

A

Exist between all particles, thought to occur due to the formation of temporary instantaneous dipoles caused by uneven spread of electrons

38
Q

What are london dispersion forces responsible for?

A

Attractive forces between non-polar moleculars and although they are weak, they increase with increasing mass

39
Q

What is the only force of attraction between non-polar molecules?

A

London dispersion force

40
Q

Why do molecules with only london dispersion forces have low boiling/melting points?

A

Only a small amount of energy is required to overcome the london dispersion forces and seperate the molecules.

41
Q

Dipole-dipole forces of attraction

A

Polar molecules attracted to other polar molecules by electrostatic attractions

42
Q

Dipole

A

When electrons are shared unequally between atoms in the same molecule due to a high difference in the electronegativity which causes a separation of charges

43
Q

Hydrogen bonding

A

When a molecule containing hydrogen bonds directly to one of the three most electronegative atoms (F, N, O)

44
Q

What is the order of strength of van der waal’s forces?

A

London dispersion < dipole-diole < hydrogen bonding < covalent < ionic

45
Q

The stronger the attractive forces,

A

The less volatile the molecule and the higher the boiling point

46
Q

What happens to solubility as the polarity of a molecule increases?

A

It increases as attraction to the polar water molecules also increases.

47
Q

Why are covalent molecules poor conductors of electricity?

A

Their electrons are localised.

48
Q

How can a coordinate covalent bond be shown?

A

An arrow instead of a line

49
Q

Electron deficient

A

Atoms that can form stable covalent compounds with an incomplete octet

50
Q

How do you know if a covalent bond is polar/nonpolar?

A

Electronegativity difference of 0-0.4=non polar, 0.4-1.7=polar, 1.8+=ionic

51
Q

Chemical evidence to support benzene resonance structure

A

Undergoes substitution instead of addition reactions, only exists in one form

52
Q

Physical evidence to support benzene resonance structure

A
  • Bond lengths are all equal
  • Enthalpy of hydrogenation is low
53
Q

Delocalisation energy in benzene

A

Accounts for the extra stability due to delocalised electrons and has to be overcome before addition reactions can occur so that’s why benzene undergoes substitution reactions

54
Q

What does formal charge assume?

A

That the octet rule always work and that all atoms in the molecule have the same electronegativity

55
Q

Formal charge formula

A

Number of valence electrons - (non bonding electrons - 1/2 number of bonding electrons)

56
Q

Sigma bond

A

When two atomic orbitals combine along a line to form a molecular orbital

57
Q

Pi bond

A

When two p orbitals combine sideways to form one molecular orbital

58
Q

How many sigma/pi bonds in single/double/triple bonds?

A

Single - 1 sigma
Double - 1 sigma, 1 pi
Triple - 1 sigma, 2 pi

59
Q

sp3 hybridisation

A

Three p orbitals, 1 s orbital combine to form four sp3 orbitals

60
Q

sp2 hybridisation

A

Two p orbitals, 1 s orbital, combine to form three sp2 orbitals and one unhybridized p orbital - double bond

Mixing of one s and two p atomic orbitals, which involves the promotion of one electron in the s orbital to one of the 2p atomic orbitals. Three new sp2 orbitals equal in energy-level + one unhybridized p orbital

61
Q

sp hybridisation

A

One p orbital, 1 s orbital, form 2 hybrid orbitals and 2 unhybridized p orbitals

62
Q

What shape forms sp hybridisation?

A

Linear

63
Q

What shape forms sp2 hybridisation?

A

Trigonal planar

64
Q

What shape forms sp3 hybridisation?

A

Tetrahedral

65
Q

What forms the pi bonds in benzene?

A

The delocalised p orbitals

66
Q

Paper chromatography

A

Used to seperate components in a mixture - spot of mixture rises up paper depending on it’s affinity for the phase

67
Q

Thin layer chromatography

A

Alumina on a glass plate is use and components partition between solvent and paper

68
Q

Liquid column chromatography

A

Sample is placed on a packed column, solvent is poured down the column and so seperated.

69
Q

Gas-liquid chromatography

A

Used to analyse voliate substances in the gas phase. Mobile phase is the inert gas that carries molecules through the analyte.

70
Q

What is the preferred formula?

A

The formula where all atoms have formal charge closest to zero

71
Q

Single bond trends (hybridisation, arrangement, pi v sigma)

A

1 sigma bond, sp3 hybridisation, tetrahedral shape

72
Q

Double bond trends (hybridisation, arrangement, pi v sigma)

A

1 sigma, 1 pi bond, sp2 hybridisation, trigonal planar shape `

73
Q

Triple bond trends (hybridisation, arrangement, pi v sigma)

A

1 sigma, 2 pi bonds, sp hybridisation, linear arrangement

74
Q

Benzene hybridisation

A

All 6 carbons have sp2 hybridisation and the 6 p atomic orbitals with one electron each form a delocalised pi bond above and below the plane of the molecule that contains 6 electrons

A HL Chemistry 2024/2025 (18 decks)

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