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Advanced higher chemistry > Molecular structure, molecular orbitals, stereochemistry > Flashcards

Molecular structure, molecular orbitals, stereochemistry Flashcards

1
Q

What is empirical formula

A

A simple formula which shows the ratio of atoms in a molecule

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2
Q

How do you obtain the empirical formulae

A

Through elemental microanalysis

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3
Q

How do you obtain molecular formula

A

You need the empirical formula and the relative molecular mass

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4
Q

How can you obtain the relative molecular mass

A

Through spectrometry

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5
Q

What is skeletal structural formula

A

An abbreviation which represents carbon-to-carbon framework through lines

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6
Q

What does the molecular orbital model indicate

A

Electrons in atoms occupy the atomic orbitals and electrons in molecules occupy molecular orbitals

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7
Q

When is an orbital full

A

When it contains 2 electrons of opposite spin

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8
Q

How are molecular orbitals made

A

By combining atomic orbitals (the number of molecular orbitals formed is equal to the number of atomic orbitals that combine)

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9
Q

What is a bonding molecular oribital

A

A molecular orbital that has less energy than the 2 atomic orbitals that made it

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10
Q

What is an antibonding molecular orbital

A

A molecular orbital with a higher energy level than the 2 atomic orbitals that combined to produce it.

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11
Q

Whats the difference between bonding/antibonding molecular orbits

A

Bonding molecular orbits embrace both nuclei whereas antibonding molecular orbital doesn’t. Antibonding molecular orbitals have more energy.

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12
Q

How is a sigma bond produced

A

When the atomic orbitals overlap along the axis of a covalent bond.

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13
Q

What can a sigma bond be referred to as

A

‘end-on’ overlap

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14
Q

How do two parallel p orbitals bond

A

Bond laterally - ‘side-on’ and form a Pi bond

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15
Q

How do Pi bonds arise

A

When Atoms form multiple bonds

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16
Q

Whats the difference between ‘side-on’ and ‘end-on’ overlaps

A

‘side-on’ overlaps are less efficient and which means Pi bonds are weaker than sigma bonds

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17
Q

Define hybridisation

A

The process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals.

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18
Q

What is an sp*3 hybrid orbital

A

when the one ‘2s’ orbital mixes with the 3 ‘2p’ orbitals to form 4 hybrid orbitals.

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19
Q

Why do degenerate sp*3 orbitals point towards the corners of a tetrahedron

A

To minimise repulsion

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20
Q

How can you tell how many hybrid orbitals were formed

A

It is equal to the number of atomic orbitals that were mixed

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21
Q

How do alkanes form bonds

A

The carbons 4 ‘sp3’ orbitals overlap ‘end-on’ with other hydrogens (1s orbitals) and carbons (sp3 orbitals) to make 4 sigma bonds which will adopt a tetrahedral arrangement.

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22
Q

How does bonding in alkenes occur with reference to orbitals

A

2 p orbitals mix with the s orbital to make 3 sp*2 orbitals while the remaining 2p orbital is left unhybridised

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23
Q

Why do sp*2 orbitals lie in a trigonal pyramidal arrangement

A

To minimise repulsions

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24
Q

How do carbons bond in alkenes

A

The 3 sp*2 (from 1 2s mixing with 2 2p) hybrid orbitals make sigma bonds with two hydrogens and the other carbon while the unhybridised 2p orbital (on the carbon) overlap ‘side-on’ to form a pi bond

25
Q

Whats the difference between carbons that are in a double bond and carbons that aren’t

A

Carbons in the double bond form sp2 orbitals and a 2p orbital while single carbons have 4 sp3 orbitals

26
Q

What are the three types of bonds that exist between atoms

A

non-polar covalent
polar covalent
ionic

27
Q

What does the slight charge of a polar covalent bond indicate

A

The more polar the bond, the greater the ionic character

28
Q

Describe the electron orbital of a non-polar covalent bond

A

Completely symmetrical.

29
Q

Describe the electron orbital of a polar covalent bond

A

Asymmetrical. The orbit skews towards the atom with the greater electronegativity.

30
Q

Describe the electron orbital of an ionic bond

A

The orbital embraces only one atom in the bond which causes extreme asymmetry where an atom has effectively been stripped off its electrons.

31
Q

Why are transition metals coloured

A

They absorb visible light which moves electrons to a higher energy state

32
Q

Why are most organic compounds colourless

A

The wavelength of the light absorbed doesn’t lay in the visible range of the electromagnetic spectrum (the energy gap between the homo and lumo orbitals is too large)

33
Q

What is the orbital which contains electrons with the highest energy called

A

Highest occupied molecular orbital (homo)

34
Q

What is the orbital which contains electrons with the lowest energy called

A

Lowest unoccupied molecular orbit (lumo)

35
Q

What type of energy does the homo - lumo gap correspond to

A

UV

36
Q

Describe the structure of most coloured molecules

A

Relatively large numbers of carbons, multiple double bonds/benzene rings

37
Q

What is the importance of a coloured molecules structure

A

It allows the molecule to have delocalised electrons across carbon atoms

38
Q

What happens if a molecule has a large degree of conjugation

A

It is likely to be coloured

39
Q

How can a molecule have a conjugated system

A

It must have a chain of alternating sigma and pi bonds or benzene rings that allow electrons to be delocalised across a number of carbon atoms.

40
Q

How does the length of the carbon chain in the conjugated system affect the colour of the molecule

A

The colour arises as the electrons absorb energy and move from HOMO to LUMO, the colour of the molecule is the colour complementary to that absorbed

41
Q

Explain the HOMO - LUMO gap with regards to degree of conjugation

A

The greater the degree of conjugation, the smaller the HOMO -LUMO gap and therefore less absorbed energy

42
Q

Define chromophore

A

The group of atoms in a molecule responsible for the absorption of light in the visible region of the em spectrum

43
Q

What is an isomer

A

Molecules that have the same molecular formula but differ in the way their atoms are arranged

44
Q

Describe the ways atoms can be arranged differently in isomers

A

The isomers bond together in a different order
(structural isomers)

The order of bonding is the same but the arrangement of atoms in the space is different (stereoisomers)

45
Q

What are the 2 types of stereoisomerism

A

Geometric and optical

46
Q

What is geometrical stereoisomerism

A

There is a carbon to carbon double bond and the bonds are fixed so it is impossible to rotate one end of the molecule to create the other isomer.

Can also occur in saturated rings where rotation around the c-c single bond is restricted

47
Q

What is optical stereoisomerism

A

The molecule is trigonal planar and an atom will join on one side or the other to create two different tetrahedral molecules (the isomers are mirror imaged and are non-superimposable).

48
Q

What are the two names given to geometric isomers

A

Cis

Trans

49
Q

What is another name for an optical isomer

A

An enantiomer

50
Q

What does non-superimposable mean

A

The molecules cannot be placed on top of one another to make the same molecule

51
Q

What type of molecules are optical isomers

A

Chiral molecules

52
Q

In what way are optical isomers non-identical

A

Identical in every physical property except their effect on plane polarised light

53
Q

How does a polariser turn light into plane-polarised light

A

Cuts out all vibrations of a light wave except for those on a particular plane

54
Q

How does geometric isomerism arise

A

Lack of free rotation around a bond (usually a carbon to carbon double bond).

55
Q

Explain the differences of optical isomers when plane polarised light passes through them

A

A wave passing through one isomer will rotate in the opposite direction at the same angle as another wave coming through the other isomer

56
Q

What would be the effect of plane-polarised light through an equimolar solution of both isomers? Why?

A

There would be no effect as the rotational effect of the molecule would be cancelled out by the anti-rotational effect of the other isomer.

57
Q

What is the term used to describe a mixture of both isomers that has no effect on plane-polarised light

A

Optically inactive

58
Q

What is the name given to an optically inactive, equimolar mixture

A

Racemic

Advanced higher chemistry (3 decks)

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