1.1 - Atomic Structure

Question 1

What is the mass of an electron?

Answer 1

1/2000

Question 2

What is mass number?

Answer 2

Number of protons and neutrons in the nucleus

Question 3

What is an isotope?

Answer 3

Atoms with the same number of protons but a different number of neutrons.

Question 4

What did John Dalton describe atoms as?

Answer 4

Solid spheres. Different spheres make up different elements.

Question 5

What did J.J. Thomson describe atoms as?

Answer 5

He discovered electrons and showed that atoms weren’t solid and indivisible. He formed the plum pudding model, with a positively charged “pudding” and negative electrons scattered on it.

Question 6

Describe the gold foil experiment.

Answer 6

Ernest Rutherford and his students conducted this experiment. They fired positive alpha particles at a thin sheet of gold. The plum pudding model suggested that most alpha particles would be slightly deflected by the positive pudding. Instead, most of the particles passed straight through and small number were deflected backwards. Most of the atom is empty space.

Question 7

What was Bohr’s model?

Answer 7

Electors exist in shell. When electrons move between shells, electromagnetic radiation is emitted or absorbed. This fitted experimental observations.

Question 8

What was discovered after Bohr’s model?

Answer 8

Not all electrons in a shell have the same energy. Sub-shells were included, explaining bonding and ionisation energy trends.

Question 9

What is relative atomic mass /Ar

Answer 9

Average mass of an atom of an element compared to 1/12 of a carbon-12 atom

Question 10

What is relative isotopic mass? What’s special about it compared to Ar?

Answer 10

Mass of an atom of an isotope of an element compared to 1/12 of a carbon-12 atom. Ar is usually not a whole number, whereas relative atomic mass is usually a whole number.

Question 11

What is relative molecular mass/ Mr

Answer 11

The average mass of a molecule compared to 1/12 of a carbon-12 atom.

Question 12

What is electrospray ionisation?

Answer 12

Dissolve the sample and push through a small nozzle at a high pressure. Apply a high voltage to it. Each particle gains a H+ ion.

Question 13

What is the equation for electrospray ionisation?

Answer 13

X (g) + H^+ -> XH^+ (g)

Question 14

What is electron impact ionisation?

Answer 14

Sample is vaporised and an electron gun fires high energy electrons at it, knocking one electron off each particle to form 1+ ions

Question 15

What happens in acceleration TOF?

Answer 15

Positively charged ions are accelerated by an electric field so they all have the same kinetic energy. Lighter ions move faster than heavier ions.

Question 16

What happens in Ion drift TOF?

Answer 16

Ions enter a region with no electric field, so lighter ions drift faster than heavier ions.

Question 17

What happens in detection TOF?

Answer 17

Lighter ions reach detector faster than heavier ions (in less time). Detector detects charged particles and forms an electric current when it is hit.

Question 18

What does a mass spectrum tell you?

Answer 18

Y axis is abundance, x axis is m/z ratio. If the sample is an element, each line will represent a different isotope. The height of each peak would represent the relative isotopic abundance.

Question 19

What would be the difference in a mass spectrum graph if electrospray ionisation is used?

Answer 19

H+ ion is added to each particle. Therefore each peak would be one unit greater than the relative mass of each isotope.

Question 20

How do you calculate Ar from a mass spectrum?

Answer 20

(Abundance 1 x m/z 1) + (Abundance 2 x m/z 2)… / total abundance

Question 21

What is the exception in electron configurations?

Answer 21

4s before 3d

Question 22

Why are chromium and copper weird? What are their electron configurations?

Answer 22

They donate one of their 4s electrons to the 3d sub-shell. It is more stable with a full or half-full d sub-shell.
Cr (24e) - 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Cu (29e) - 1s2 2s2 2p6 3s2 3p6 4s1 3d10

Question 23

What’s different about transition metals in terms of electron configuration?

Answer 23

When they become ions, they lose their 4s electrons before their 3d electrons.

Question 24

From left to right on the period table, what are the blocks for the outer shell electrons?

Answer 24

S, d, p

Question 25

What decides the chemical properties of an element?

Answer 25

Electronic structure.

Question 26

What is first ionisation energy?

Answer 26

Energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 27

What are the three factors affection ionisation energy? Explain them.

Answer 27

Nuclear charge. More protons, stronger nuclear charge and stronger attraction between nucleus and outer electron.
Distance from nucleus. Further away means less attraction between nucleus and outer electron.
Shielding. Increases shielding reduces attraction between nucleus and outer electron.

Question 28

Why does ionisation energy increase within each shell?

Answer 28

More protons, stronger nuclear attraction between nucleus and electron. Same shielding.

Question 29

What do big jumps in ionisation energy show?

Answer 29

New shell closer to nucleus.

Question 30

Why does ionisation energy decrease down group 2?

Answer 30

More number of shells, electrons further distance away from nucleus, more shielding.

Question 31

Across the period, between which groups are the first drop in ionisation energy? Why? Give an example.

Answer 31

Groups 2 and 3. There is a drop from magnesium to aluminium. Aluminium’s outer elector is in a 3p orbital, which has a higher energy and more shielding than the outer electron of magnesium which is in a 3s orbital.

Question 32

Where does the second drop occur across the period? Why? Give an example.

Answer 32

Between groups 5 and 6. From phosphorus to sulfur, the shielding is identical because the electron is being removed from an identical orbital. In phosphorus the electron is single, and in in sulfur the electron is in a pair. Therefore there is repulsion and it is easier to remove the outer electron from the shared orbital.

Question 33

Where is the second ionisation energy of sulfur compared to phosphorus?

Answer 33

Higher

Question 34

Give a reason why the second ionisation energy of silicon is lower than the second ionisation energy of aluminium.

Answer 34

Electron in silicon is removed from 3p orbital which has a higher energy than the 3s orbital for the electron in aluminium. Or you could say the electron in silicon is more shielded.

Question 35

What is the technique in exam style questions about ionisation energy?

Answer 35

Talk about the orbital that the outer electron is REMOVED from.

Question 36

Why are ionisation energies endothermic?

Answer 36

Energy needed to overcome the attraction between the negative electron and positive nucleus.

Question 37

What is important when writing ionisation equations.

Answer 37

Remember GASEOUS!

Question 38

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

Answer 38

The ions produce a current and gain an electron.
The size of the current determines the relative abundance.