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chemistry: organic > topic 1 - atomic structure and the periodic table > Flashcards

topic 1 - atomic structure and the periodic table Flashcards

1
Q

What are atoms made up of?

A

Atoms are made up of three subatomic particles - protons, neutrons and electrons.

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2
Q

Where is most of the mass of the atom concentrated?

A

Most of the mass of the atom is concentrated in the nucleus as it consists of protons and neutrons.

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3
Q

Where are electrons located in an atom?

A

Electrons surround the nucleus in orbitals which take up most of the volume of the atom.

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4
Q

What is the atomic number?

A

The number of protons in the nucleus of an atom - this is also the number of electrons in a neutral atom (if imbalanced, atom will have a charge and become an ion).

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5
Q

What is the mass number?

A

The number of protons and neutrons in the nucleus of an atom.

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6
Q

What are isotopes?

A

Atoms with the same number of protons in the nucleus but a different number of neutrons (same atomic number, different mass number).

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7
Q

Why do isotopes have the same chemical properties?

A

Same chemical properties as it is decided by the number and arrangement of electrons.

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8
Q

Why do isotopes have different physical properties?

A

Different physical properties as it depends on the mass of the atom.

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9
Q

What is relative isotopic mass?

A

The average mass of one atom of an isotope to one twelfth of the mass of a carbon-12 atom. They are not always whole numbers as the mass of a proton is slightly less than the mass of a neutron (usually are whole numbers).

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10
Q

What is relative atomic mass (RAM)?

A

The average mass of an atom of an element (containing mixture of isotopes) relative to one twelfth the mass of a carbon-12 atom. They are the average value for the mixture of isotopes found naturally, so not in whole numbers.

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11
Q

What is relative molecular mass?

A

The average mass of a molecule relative to one twelfth the mass of a carbon-12 atom.

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12
Q

What is mass spectrometry used for?

A

Mass spectra are produced by mass spectrometers which can identify and compare the relative isotopic masses and relative abundances of different elements by separating atoms/molecules according to mass.

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13
Q

Why is mass spectrometry necessary?

A

It is used as individual atoms are far too small to be counted and weighed.

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14
Q

What happens first in mass spectrometry?

A

A gaseous sample is placed into the device.

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15
Q

What happens during ionisation in mass spectrometry?

A

Ionisation of the sample by the bombardment with electrons so before detection, atoms/molecules converted to positive ions in gaseous/vapour state.

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16
Q

Why is there a high vacuum in a mass spectrometer?

A

High vacuum inside mass spectrometer to prevent interference from atoms and molecules in air.

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17
Q

How are ions accelerated in a mass spectrometer?

A

Positive ions accelerated towards negatively charged detection plate due to an electric field.

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18
Q

How are ions separated in a mass analyser?

A

The mass analyser separates ions by mass:charge ratio (m/z).

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19
Q

How does a magnetic field affect ion paths in mass spectrometry?

A

Ions deflected by a magnetic field into a curved path.

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20
Q

How does mass affect ion deflection?

A

The higher the mass, the less deflection.

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21
Q

How does charge affect ion deflection?

A

The higher the positive charge, the more deflection.

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22
Q

How does the ion detector work in mass spectrometry?

A

Ion detector detects and counts the number of each different m/z value; a spectrum is generated by ICT.

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23
Q

What causes a current in the detector?

A

When positive ions hit negatively charged detection plate, they gain an electron producing a flow of charge.

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24
Q

What determines the size of the current in the detector?

A

The greater the abundance, the greater the current produced.

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25
What can be interpreted from a mass spectrum graph?
From this graph the isotopic composition and its relative abundances as well as the relative atomic masses/ relative molecular masses can be seen.
26
What happens if an ion has a double charge?
Ions with a double charge can be produced if it is affected more by the magnetic field producing a curved path of smaller radius. This means its m/z ratio is halved and seen on the graph as half the expected m/z value as a small peak (abundance remains the same).
27
How do you calculate RAM from a mass spectrum?
Multiply each relative isotopic mass by its relative isotopic abundance, and add up the results. Divide by the sum of isotopic abundances.
28
What determines the highest peak in a mass spectrum?
Highest peak at molecules which are more abundant
29
What are principal energy levels in atoms?
Electrons orbit the nucleus in principal energy levels or shells, which are given numbers known as principal quantum numbers.
30
Why do outer shells have more energy?
Shells further from the nucleus have a greater energy level than the shells close to the nucleus.
31
How do subshells and orbitals exist?
These shells contain different types of subshell or sub energy levels which have different number of orbitals.
32
What is an orbital?
A region of space in the atom where electrons move randomly. They can hold up to two electrons with opposite spins
33
How are orbitals defined?
Each orbital is defined by its energy level, shape and direction in space.
34
What are the shapes of s and p orbitals?
s-orbitals are spherical whereas p-orbitals have dumbbell shapes; there are three p-orbitals and they're at right angles to one another.
35
How do electrons occupy orbitals?
Orbitals within the same subshell have the same energy - electrons occupy the lowest energy orbitals before they fill the highest energy orbitals.
36
Why must electrons in an orbital have opposite spins?
The electrons in each orbital have to ‘spin’ in opposite directions so that atom is stable as the magnetic attraction resulting from their opposite spins can counteract the electrical repulsion from their negative charges - this is called spin-pairing.
37
Why do electrons occupy orbitals singly first?
Electrons occupy orbitals singly before pairing up, to minimise repulsion (aufbau principle.
38
Why do some atoms rearrange electrons for stability?
If electrons spins are unpaired and therefore unbalanced, it produces a natural repulsion between the electrons making atom very unstable. If this is the case, electrons may take on a different arrangement to improve stability.
39
Why is the gap between higher shells smaller?
As electron shells move farther from the nucleus, they become closer in energy, meaning the energy gap between the second and third shells is smaller than that between the first and second.
40
What happens when 3d and 4s orbitals overlap?
By the fourth shell, the 3d orbital (highest energy in the third shell) overlaps with the 4s orbital (lowest energy in the fourth), so the 4s, 3d, and 4p orbitals fill in that order placing d-block elements accordingly though the 4s electrons are lost first when these elements ionise.
41
What is electromagnetic radiation?
Electromagnetic radiation is energy that’s transmitted as waves, with a spectrum of different frequencies.
42
How does frequency and wavelength change along the electromagnetic spectrum?
Along the spectrum, the radiation increases in frequency and decreases in wavelength.
43
Where are electrons located in their ground state?
In their ground state, atoms have their electrons in their lowest possible energy levels.
44
What happens when electrons absorb energy?
If excited, electrons absorb energy and can move up energy levels which will be evident in electronic configuration.
45
What happens when excited electrons return to lower energy levels?
They emit energy and drop down to lower energy levels and back to ground state.
46
Why do line spectra support give evidence of discrete energy levels?
A line spectrum shows the frequencies of light emitted when electrons drop down from a higher energy level to a lower one, supporting the idea that electrons exist in discrete energy levels.
47
What determines the wavelength of light emitted by electrons?
As the energy of shells is fixed and the distance between them, the radiation will have a fixed frequency.
48
Why do electrons not emit any wavelength in between transitions?
The electrons can only exist in these fixed orbitals, and not anywhere in between.
49
Why are some lines visible and others not in a spectrum?
The wavelength of light is only seen if emitted within the visible region.
50
What does each set of spectral lines represent?
Each set of lines represents electrons moving to a different energy level, supporting the fact that energy levels are discrete and electrons directly 'jump' from one energy level to the next.
51
Why do spectral lines get closer together?
These lines get closer together as the frequency increases.
52
What would happen if energy levels weren't discrete?
If shells/subshells didn’t exist, any wavelength of light can be emitted and white light can be observed, electrons take any energy on continuum
53
What is the first ionisation energy?
The energy needed to remove one electron from each atom in a mole of gaseous atoms to form one mole of gaseous ions with a single positive charge.
54
Why is ionisation an endothermic process?
This is an endothermic process as energy is absorbed to ionise an atom or molecule and overcome attraction between an electron and the nucleus.
55
What does a high ionisation energy indicate?
A high ionisation energy means there's a strong attraction between the electron and the nucleus, so more energy is needed to overcome the attraction and remove the electron. Each time an electron is removed there is a successive ionisation energy which is evidence to support the idea of electron subshells
56
How does nuclear charge affect ionisation energy?
As the number of protons increases, the more positively charged the nucleus is and the stronger the attraction for outermost electrons.
57
How does atomic radius affect ionisation energy?
As the distance increases, the weaker the attraction between the positive nucleus and the outermost electron.
58
How does shielding affect ionisation energy?
Inner shells create a ‘barrier’ that reduces attraction between the positive nucleus and electrons (effective nuclear charge).
59
What does a graph of successive ionisation energies show?
A graph of successive ionisation energies is evidence to support the idea that electrons exist in energy levels within atoms and suggests the group to which the element belongs.
60
What indicates a new energy level on an ionisation graph?
A sudden large increase indicates a change in energy level. This is because the electron being removed is from an orbital closer to the nucleus so more energy is required.
61
Why do successive ionisations require more energy?
Electrons are being removed from an increasingly positive ion. Less repulsion amongst the remaining electrons, so they're held more strongly by the nucleus.
62
How can group number be determined from an ionisation energy graph?
By observing the number of electrons removed at the lowest energy before a large change in energy.
63
Why is the outer electron more easily removed?
The outer electron is relatively easily removed due to shielding which reduces attraction.
64
What is periodicity?
Periodicity is the repeating pattern of physical or chemical properties going across the periods.
65
How is the modern periodic table arranged?
It arranges elements by atomic number.
66
What do elements in a period have in common?
All the elements in a period have the same number of electron shells, so there are repeating trends in physical and chemical properties.
67
What do elements in a group have in common?
All the elements in a group have the same number of electrons in their outer shell, so there is a trend of similar chemical properties.
68
Why does ionisation energy increase across a period?
Atomic number increases so nuclear charge increases, pulling electrons closer, decreasing atomic radius and increasing ionisation energy, no effect of shielding
69
Why does ionisation energy decrease down a group?
Number of shells increases so atomic radius increases and shielding reduces the effect of nuclear charge, making electrons easier to remove.
70
Why is first ionisation energy lower for Al than Mg?
* In aluminium outer electron is in a 3p orbital rather than a 3s like magnesium. The electrons in 3p orbital has a slightly higher energy than the 3s orbital, so the electron is, on average, to be found further from the nucleus. * The 3p orbital has additional shielding provided by the 3s2 electrons. * Both these factors together are strong enough to override the effect of the increased nuclear charge
71
Why is first ionisation energy lower for S than P?
* The shielding is identical in both atoms, and the electron is being removed from an identical 3p orbital. * In phosphorus, the electron is being removed from a singly-occupied orbital. But in silicon the electron is being removed from an orbital which is spin-paired with two electrons. * The repulsion between two electrons in an orbital means that electrons are easier to remove from shared orbitals, overriding effect of increased nuclear charge
72
Why has Na a much lower first ionisation energy than Neon?
This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. So Na’s outer electron is easier to remove and has a lower ionisation energy
73
Why has helium the largest first ionisation energy?
Its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. He has a bigger first ionisation energy than H as it has one more proton
74
What is the bonding for period 2 and 3 elements?
* Na, Mg, Al - metallic bonding, charge density (atomic radius) * Si - macromolecular: many strong covalent bonds between atoms * Cl2 (g), S8 (s), P4 (S) - simple molecular - S8 has a higher mp than P4 because it has more electrons (S8 =128)(P4=60) so has stronger London forces between molecules * Ar - monoatomic, weak London Forces between atoms

chemistry: organic (6 decks)

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