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A level Chemistry AQA > The atomic structure > Flashcards

The atomic structure Flashcards

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1
Q

What did John Dalton suggest about the atom?

A

They were indivisible (they could not be broken down) and all the atoms of a particular element had the same mass.

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2
Q

What did Henri Becquerel discover about the atom?

A

He discovered radioactivity ,which showed that particles could come from inside the atom

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3
Q

What did JJ Thompson discover about the atom?

A

He discovered the electron and showed that electron were negatively charged an electrons from all elements were the same. He suggested that the electrons were located within the atom in circular arrays, like plums in the pudding of positive charge (plum pudding model)

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4
Q

What did Ernest Rutherford and his team find out about the atom?

A

most of the mass and all the positive charge of the atom was in a tiny central nucleus

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5
Q

What are proton and neutrons also called and why?

A

Nucleons because they are found in the nucleus

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6
Q

What forces are protons and neutrons held together by?

A

strong nuclear force

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7
Q

Compare nuclear forces and electrostatic forces

A
  • Nuclear forces are stronger = Because it’s stronger than electrostatic forces, nuclear forces can overcome the repulsion between protons in the nucleus.
  • Nuclear forces act between protons and neutrons instead of electrons and protons. Nuclear forces act only over very short distances, that is, within the nucleus.
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8
Q

Instead of particles, what are electrons considered to be?

A

A cloud of negative charge

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9
Q

What volume of space does an electron fill?

A

atomic orbital

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10
Q

What is the importance of an atomic orbital?

A

it influences the shape of molecules

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11
Q

What determines the chemical properties (how it reacts) of an element?

A

The number of electrons in the outer shell of an atom

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12
Q

What do all atoms of the same element have?

A

The same atomic number

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13
Q

Why do different isotopes of the same element react chemically in the exact same way?

A

Because they have the same electron configuration

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14
Q

What happens when isotopes are unstable?

A

The nucleus of the atom breaks down giving off bits of the nucleus or energetic rays. This causes radioactivity.

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15
Q

The rate of radioactive isotope decaying is measured by what?

A

half life

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16
Q

What is the half-life?

A

the time taken for half of its radioactivity to decay

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17
Q

What idea did Niels Bohr put forward about the atom?

A
  • That the atom consisted of a tiny positive nucleus orbited by electrons to form an atom like a tiny solar system.
  • Electrons orbited in shells of fixed size
  • The movement of electrons from one shell to the next explained how atoms absorbed and gave out light
  • This was the beginning of quantum theory.
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18
Q

What did Erwin Schrodinger discover about the atom?

A

He worked out an equation that used the idea that electrons had some of the properties of waves as well as particles = quantum mechanics, which predicts the behaviour of sub atomic particles

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19
Q

What did James Chadwick discover about the atom?

A

Neutron

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20
Q

What did Gilbert Lewis discover about bonding?

A
  • The inertness of the noble gases was related to their having full out shells of electrons
  • Ions were formed by atoms losing or gaining electrons to attain full out shells
  • Atoms could also bond by sharing electrons to form full out shells
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21
Q

What is the formula for the number of electrons in each shell?

A

2n^2

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22
Q

What does a mass spectrometer do?

A

gives accurate information about the relative isotopic mass and also about the relative abundance of isotopes. It determines the mass of separate atoms

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23
Q

How are relative atomic masses measured and why is it measured this way?

A

They are measured on a scale on which the mass of an atom of C(12) is defined as exactly 12. This is because no other isotope has a relative atomic mass that is exactly a whole number due to the proton and the neutron both not having an exact mass of 1

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24
Q

What is a mass spectrometer used for?

A

Mass spectrometry can be used :

  • to identify elements.
  • to determine relative molecular mass.
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25
Q

Give an outline of what happens in a time of flight mass spectrometer

A

the substances in the sample are converted to positive ions, accelerated to high speed (which depend on their mass to charge ratio), and arrive at a detector

26
Q

What are the 5 steps in TOF mass spectrometer?

A

1) ionisation
2) acceleration
3) ion drift
4) Detection
5) data analysis

27
Q

Why are mass spectrometers kept in a Vacuum?

A

the whole apparatus is kept under a high vacuum to prevent the ions that are reduced colliding with molecules from the air

28
Q

What are the two different types of ionisation?

A

Electrospray and electron impact ionisation

29
Q

What happens during Electrospray Ionisation?

A

the sample to be investigated is dissolved in a volatile solvent and injected through a fine hypodermic needle to give a fine mist. The tip of the needle is connected to the positive terminal of a high voltage supply.

The particles are ionized by gaining a proton from the solvent as they leave the need;e producing the XH+ ions

The solvent evaporates away white the XH+ are attracted towards the negative plate, where they are accelerated

30
Q

What happens during electron impact ionisation?

A

The sample is vaporized and high-energy electrons are fired at it from an electron gun, which is a hot wire filament with a current running through it that emits a beam of high-energy electrons. This usually knocks off one electron from each particle forming a 1+ ion

31
Q

What happens during Acceleration?

A

The positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed

32
Q

What happens during Ion drift?

A

the ion pass through a hole in the negative charged plate, forming a beam and travel along a tube, called the light tube, to a detector

33
Q

What happens during Detection?

A

When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. the flight times are recorded. The positive ions are discharged when they hit the detector plate, generating a movement of electrons and hence causes a current to flow. The size of the current gives a measure of the number of ions hitting the plate.

34
Q

What happens during Data analysis?

A

The signal from the detector is passed to a computer which generates a mass spectrum

35
Q

What is the shape of an s orbital?

A
36
Q

What is the shape of a p orbital?

A
37
Q

What does the shape of the orbitals represent and how do they influence molecules?

A

a volume of space in which there is a 95% probability of finding an electron and they influence the shapes of molecules

38
Q

Describe the concept of an electron spin

A

two electrons in the same orbital must have opposite spins

39
Q

What is high-resolution mass spectrometry?

A

when the relative atomic masses are measured to 5 decimal places of an atomic mass unit

40
Q

What is low-resolution mass spectrometry?

A

when relative atomic masses are measured to one decimal place

41
Q

Why is there sometimes a very low mass/charge ratio on the mass spectrum?

A

due to fragments caused by the break up of molecular ions = fragmentation

42
Q

Why are there some peaks with higher m/z ratios?

A

due to some molecules containing isotopes

43
Q

Explain how ions are detected and relative abundance is measured in a TOF mass spectrometer

A

Ions hit the negative detector plate , each ion gains an electron, which generates a movement of electrons and hence a current is measured. The abundance is proportional to the size of the current

44
Q

Explain why it is necessary to ionise molecules when measuring their mass in TOF

A

only ions will create a current at the detector and pick up electrons

only positive ions are accelerated (by an electric field)

45
Q

What is ionization energy?

A

the enthalpy change when we remove 1 electron from each atom in 1 mole of gaseous atoms to produce 1 mole of gaseous 1+ ions

46
Q

Which elements fill up 3d before 4s

A

Chromium and copper

47
Q

Describe successive ionisation energies?

A
  • The first electron needs the least amount of energy to be removed because it is being removed from a neutral atom (first IE)
  • Second electron = more energy = being removed from a 1+ ion ( second IE)
  • so on and so on
48
Q

The term ionisation energy is only used for what?

A

the formation of positive ions

49
Q

What is electron affinity?

A

the energy change when each atom in one mole of gaseous atoms gains one electron to form mole of gaseous -1 ions

50
Q

What are the three main factors that affect ionisation?

A
  1. The attraction of the nucleus (The more protons in the nucleus the greater the attraction)
  2. The distance of the electrons from the nucleus (atomic radius) (The bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus)
  3. Shielding of the attraction of the nucleus (An electron in an outer shell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus)
51
Q

What can successive electron configuration tell us about the electron configuration of an atom? (use the picture as an example)

A

there is a gradual increase in ionisation energy as we remove the first four electrons due to successive ionisation= as we remove one electron, the remaining electron in the shell pull closer to the nucleus (greater attraction between outer electrons and nucleus).

There is a big increase in ionisation energy for the 5th and 6th electron, implying that there in the inner energy level, so the electrostatic attraction towards the nucleus is greater, hence it requires more energy for the electron to be removed

52
Q

Why is it harder to remove electrons from the first energy shell than from the second energy shell?

A

Because the first energy level is closer to the nucleus and electrons in the first shell experience must less shielding = greater attraction to the nucleus

53
Q

What happens to the ionisation energy as you move down the group and why?

A

the ionisation energy decreases because:

  • the atomic radius increases = outer electron further away from the nucleus = less attaction
  • number of internal energy levels increases = more shielding
54
Q

What happens to the ionisation energy as you move across the period and why?

A

it generally increases due to nuclear charge increasing as the number of protons increases. This increases the attraction between the electrons and the nucleus.

Because nuclear chargee is increased, the greater attractions to the electrons pulls the electron cloud closer to the nucleus, which results in a smaller atomic radius

electron shielding remains constant contributing to the increasing ionisation energy levels

55
Q

Why does the 1st ionization energy decrease between Mg and Al?

A

Al outer electron is in a p sublevel, which is a higher level than MG outer electron shell, which is in an s - sublevel. This means, that it is further away from the nucleus, so there is less attraction to the nucleus for AL outer electron than Mg’s outer electron, hence its easier to lose

56
Q

Explain why the Ist ionization energy decrease between P and S

A

Phosphorus as 3 electrons in the p-sublevel, so they are in separate orbitals. However, in sulfur, it has 4 electrons, so there is one electron par. this pair or electrons have a repulsion between them, so less energy is required for an electron to be removed.

57
Q

Why is the ionization energy of K (period 4) , much lower than the 1st ionisation energy of Ar (period 3)

A

K is a much bigger atom than Ar, so it has a bigger atomic radius and has more shielding due to the outer electrons having a weaker attraction to the nucleus

58
Q

Explain why the mass spectrometer can not be used to distinguish between 54 Cr2+ 27 Al+

A

Calculate m/z for each ion = size of current is proportional to abundance

59
Q

What is the definition of relative atomic mass?

A

the average mass of its atoms, including its isotopes, compared to 1/12th the mass of a carbon, which has a mass of 12

60
Q

What is the definition of a molecular ion?

A

the molecule with an electron knocked off

the ion with the biggest m/z ratio

61
Q

Explain why the successive ionization energies increase.

A
  • Electrons are being removed from an increaingly positive ion
  • higher proton to electron ratio, so the same number of protons are attracting less electrons
  • ions get smaller
  • less shielding
  • electrons are closer to the nuclear and nuclear charge has increased

A level Chemistry AQA (30 decks)

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