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Biosciences > Chem 1a > Flashcards

Chem 1a Flashcards

1
Q

Relative mass of electron

A

1/1836

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2
Q

Isotope

A

Have the same chemical properties as their proton and electron no. are the same. Chemical properties depend only on electron structure.

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3
Q

Mass Spectrometer

A

Instrument used to measure the relative mass of isotopes.

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4
Q

(TF) Stage One: Ionisation

A

Electron Impact (Electron Gun)
· High energy electrons from an electron gun
· Fired at the sample and knock off an electron
· X(g) → X+(g) + e-

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5
Q

(TOF) Stage Two: Acceleration

A

· Cations are accelerated by electric field to a constant kinetic energy
· Kinetic energy, KE = 1/2mv2, hence v = √(2KE/m)
· Rate at which ions are accelerated depends on mass
· Ions with a lower mass will travel faster
· Ions with a higher mass will have a lower velocity

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6
Q

(TOF) Stage Three: Ion Drift/Flight Tube

A

· Ions allowed to drift in a field-free region
· Time taken for ions to reach detector at known distance is measured
· Time depends on mass of ion. Lighter ions reach higher velocities, so low mass ions reach the detector first, high mass ions arrive last
· Mass of ion can be determined from time taken for ion to reach detector

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7
Q

(TOF) Stage Four: Ion Detection

A

· Cations that reach detector pick up electrons, causing current to flow in ion-current detector
· Greater abundance of ion = bigger current produced
· Detector linked to an amplifier and a recorder, which converts the current into a peak, shown in a mass spectrum
· Height of peak is proportional to size of current generated, so is proportional to abundance of ion

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8
Q

(TOF) Stage Five: Data Analysis

A

Flight times are analysed and recorded as a plot of abundance v mass/charge (m/z)

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9
Q

Mass spectra graphs show

A
  • m/z for each ion on the x-axis

- relative abundance for each ion on the y-axis

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10
Q

Mass spectra can be used to

A
  1. identify unknown elements
  2. calculate Ar values for known elements
  3. calculate the Mr values for molecular substances
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11
Q

Mass number

A

Total number of protons and neutrons in nucleus

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12
Q

Orbital

A

Sub-units of equal energy which make up sub-levels

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13
Q

Rule of how elements fill up their shells

A
  1. Electrons fill lowest energy levels first.
  2. Each orbital has maximum 2 electrons.
  3. 2 electrons in same orbital have opposite spin.
  4. Orbitals of same energy fill singly before pairing up.
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14
Q

First ionization energy

A

Energy required to remove 1 mole of e- from 1 mole of gaseous atoms as shown by the following equation,
X(g) –> X+(g) + e–

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15
Q

Factors affecting how strongly the outer electron is held in an atom.

A

· Nuclear charge
· Distance between nucleus and electron i.e. the radius of the particle.
· Shielding - the more full shells there are, the greater they interfere with attraction.

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16
Q

General trend for period 3

A
  • Ionisation Energy increases across period
  • Number of protons increase
  • Shielding is constant / atomic radius decreases
  • More energy is required to remove electron
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17
Q

Exceptions to general trend for period 3, group 3

A

Al (group 3)
• IE decreases
• Electron is removed from higher energy p sub-level
• Less energy required to remove electron

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18
Q

Exceptions to general trend for period 3, group 6

A

S (group 6)
• IE decreases
• Pair of electrons in p-orbital
• Extra repulsion = less energy required to remove electron

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19
Q

Ar

A

Ar = average mass of one atom of an element x 12/mass of one atom of carbon–12

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20
Q

Mr

A

Mr = average mass of one ‘particle’ of a substance x 12/mass of one atom of carbon–12

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21
Q

Mole

A

Amount of a substance in g, which contains the same no. of particles as there are atoms in 12g of carbon–12.

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22
Q

Assumptions of gases for ideal gas equation

A

· Identical particles in continuous random motion.
· Particles have no appreciable volume themselves.
· Collisions between particles are perfectly elastic i.e. there is no loss of (kinetic) energy on collision.
· No forces between the particles.

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23
Q

Empirical formula

A

EF represents the simplest ratio of atoms of each element in a compound.

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24
Q

Molecular formula

A

MF represents the actual number of atoms of each element in one molecule of a substance.

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25
Q

Solute

A

Solid being dissolved

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26
Q

Solvent

A

Liquid doing the dissolving

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27
Q

Titration

A

An acid or alkaline solution is accurately added to a fixed volume of the other until neutralization just occurs. This gives the volumes of both the reacting solutions..

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28
Q

Electron impact ionisation

A

Sample is bombarded with high energy electrons which repel electrons present on the sample, causing it to lose one and gain a positive charge.

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29
Q

Electrospray ionisation

A

High voltage sample is applied to sample in polar solvent, causing the sample molecule to gain a proton forming MH+

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30
Q

Why must molecules be ionized when measuring their mass in a TOF mass spec?

A

Ions will interact and be accelerated by an electric field, and will generate a current upon hitting detector.

31
Q

Apart from the relative mass of each isotope, what else would need to be known for the Ar of an element to be calculated?

A

Relative abundance/peak height of each element

32
Q

During TOF, state what is adjusted so that each of the isotopes of an element can be detected in turn.

A

Electric field

33
Q

During TOF, how does adjusting the electric field enable the isotopes of an element to be separated?

A

Deflection depends on mass or m/z

34
Q

How is the Mr of a covalent compound obtained from its mass spectrum?

A

Highest m/z value

35
Q

Explain why chromium is placed in the d block in the Periodic Table.

A

Highest energy electron is in 3d sub-shell

36
Q

What is used in a mass spectrometer to deflect the positive ions?

A

Magnetic field

37
Q

How is an ionic compound formed?

A

Metal atom reacts w/ non-metal atom, resulting in ion formation. Oppositely charged ions R attracted to each other by electrostatic forces; forming an ionic bond.

38
Q

What affects the strength of an ionic bond?

A
  • Charge of ion

- Radius of ion

39
Q

As radius of an ion decreases, how does this affect the strength of an ionic bond?

A

Causes it to become stronger.

40
Q

As the charge of an ion increases, how does it affect the strength of an ionic bond?

A

Cause it to become stronger.

41
Q

Explain why Calcium Fluoride has a greater melting point than Calcium Chloride.

A

F- is a smaller ion than Cl-, so has a greater charge density, causing it to have a greater attraction to Ca+ which requires more energy to overcome, causing it to have a higher m.p.

42
Q

Why are ionic compounds typically soluble in water?

A

Water molecules have a slight negative charge due to the presence of lone pairs on the oxygen. Cations are attracted to them and form co-ordinate bonds. This attraction is powerful enough to overcome the ionic attractions.

43
Q

Why are ionic compounds typically insoluble in organic solvents?

A

Organic substances aren’t charged/polar, or have a very small charge which is not powerful enough to overcome the attractions in ionic compounds.

44
Q

Why can ionic compounds only conduct electricity when molten?

A

The electrons are only free to move whilst molten.

45
Q

Co-ordinate bond

A

When both electrons in the shared pair come from one of the atoms in a bond.

46
Q

Why are simple molecular substances typically gaseous at room temperature?

A

They have weak intermolecular forces between molecules so have low melting and boiling points.

47
Q

Why are simple molecular gases insoluble in water?

A

They don’t have a strong enough attraction with water to overcome the hydrogen bonds present.

48
Q

Why are simple molecular gases soluble in organic solvents?

A

Both are molecular, and are attracted to each other by van der waals forces.

49
Q

Why are simple molecular substances non-conductive?

A

There isn’t sufficient contact between the molecules to allow electrons to move through the whole solid or liquid, even when delocalised.

50
Q

Metallic bonds

A

Cations arranged in a regular giant lattice and surrounded by a ‘sea’ of delocalised electrons. Are difficult to overcome, so high mp and bp.

51
Q

Why do group 1 metals have comparatively lower mp and bp to other metals?

A
  • Inefficiently packed, so can’t form many bonds.
  • Have relatively large atoms and large distance between nuclei and electrons.
  • Only have one electron in outer energy level.
52
Q

Why are metals able to conduct electricity?

A

Delocalised electrons are free to move throughout the structure as a solid and liquid. They can cross grain boundaries.

53
Q

Why are metals malleable and ductile?

A

Atoms are able to roll over each other into new positions without breaking the metallic bond. Causes metal to be elastic.

54
Q

Why are metals so strong?

A

Have grain boundaries.

55
Q

Malleable

A

Can be beaten into sheets

56
Q

Ductile

A

Can be stretched into a wire

57
Q

Electronegativity

A

Power of an atom to attract electrons in a covalent bond.

58
Q

Electronegativity increases…

A
  • Across a Period.

- Up a Group.

59
Q

What causes a molecule to be non-polar?

A

When all atoms in the molecule have an equal charge density, causing the overall charge to cancel out.

60
Q

What cause a molecule to have ionic character?

A

When there is an uneven distribution of electron density between a shared pair of electrons, due to differences in electronegativity between atoms.

61
Q

Polarising ability

A

Ability to attract electron density

62
Q

Polarisability

A

Has electron density taken away and be polarised

63
Q

Dipole-dipole forces

A

Forces resulting in differences in polarity between molecules. Attraction due to opposing charges.

64
Q

Activation energy

A

Minimum energy needed on successful collision for particles to react.

65
Q

How does the peak on a maxwell-boltzmann distribution change when temperature increase?

A

Curve shifts to the right and lowers as there are more particles with more kinetic energy.

66
Q

Reaction rate

A

Change in conc. of product/reactant divided by time

67
Q

Factors for rate of reaction

A

Concentration or pressure.
Surface area.
Temperature
Catalysis

68
Q

Why does an increase in concentration/surface area cause an increase in reaction rate?

A

Successful collisions are more likely to occur.

69
Q

Why does an increase in temperature cause an increase in reaction rate?

A

Means particles are more likely to react upon successful collision as they possess a greater kinetic energy.

70
Q

Catalyst

A

Substance which alters chemical reaction but remains chemically unchanged at the end.

71
Q

How does a catalyst work?

A

Provide an alternative reaction route with a lower Ea.

72
Q

Order of a reagent in a reaction

A

The power to which the concentration term is raised in the rate equation.

73
Q

Overall order of a particular reaction

A

The sum of the powers of the concentration terms in the rate equation.

Biosciences (24 decks)

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