PHYSICAL CHEM - ATOMIC STRUCTURE

Question 1

What is the diameter of the nucleus?

Answer 1

approx 10^-15 m

Question 2

What is the diameter of an atom?

Answer 2

approx 10^-10 m (~100000x the diameter of the nucleus)

Question 3

What is the relative charge of a proton?

Answer 3

+1

Question 4

What is the relative charge of a neutron?

Answer 4

0

Question 5

What is the relative charge of an electron?

Answer 5

-1

Question 6

What is the relative mass of a proton?

Answer 6

1

Question 7

What is the relative mass of a neutron?

Answer 7

1

Question 8

What is the relative mass of an electron?

Answer 8

1/1840

Question 9

Why do protons not repel each other in the nucleus?

Answer 9

protons and neutrons are held together by strong nuclear force which is strong enough to overcome the repulsion between protons in the nucleus

Question 10

What are isotopes?

Answer 10

atoms of the same element with the same no. of protons but a diff no. of neutrons

Question 11

How can we use isotopes for carbon dating?

Answer 11

• some isotopes are unstable and radioactive. they become stable by emitting radiation over time
• this means that we can use the amount of an isotope in an object to work out how old it is

Question 12

What are the 4 types of sub-shell?

Answer 12

• s
• p
• d
• f

Question 13

How many orbitals does each subshell contain?

Answer 13

• s: 1
• p: 3
• d: 5
• f: 7

Question 14

How many electrons can each orbital hold?

Answer 14

2

Question 15

What is the Aufbau principle?

Answer 15

orbitals with the lowest energy are filled up first

Question 16

What is the Pauli exclusion principle?

Answer 16

each orbital can only hold 2 electrons and they must have opposite spins

Question 17

What is Hund’s rule?

Answer 17

electrons fill orbitals separately before they start sharing

Question 18

Which orbital is filled first: 3d or 4s? why?

Answer 18

4s - lower in energy than 3d

Question 19

What 2 elements are exceptions to the rules when filling up orbitals and why?

Answer 19

• copper - only fills 1 electron in the 4s orbital allowing 10 to go into the 3d orbital in order to have a more stable configuration
• chromium - only fills 1 electron in 4s and 5 go into 3d because 5 single electrons in each d orbital is more stable

Question 20

What is ionisation energy?

Answer 20

the energy required to remove 1 mole of electrons from a mole of atoms in the gaseous state (measured in KJ mol ^-1)

Question 21

What is the trend in first ionisation energy down a group?

Answer 21

IE decreases

Question 22

Explain why ionisation energies decrease when you go down a group?

Answer 22

• increase in shielding
• increase in distance of outer electron
• less attraction between outer electron and nucleus

Question 23

What is the trend in first ionisation energy across a period?

Answer 23

IE increases

Question 24

Explain why ionisation energies increase when you go across a period?

Answer 24

• increased nuclear charge
• greater force of attraction between nucleus and outer electron
• same amount of shielding

Question 25

Why is it easier to remove an electron from Al than Mg?

Answer 25

- outer electron in Al is in 3p orbital, outer electron in Mg is in 3s orbital - 3p orbital is slightly higher in energy than 3s orbital

Question 26

Why is it easier to remove an electron from sulfur (S) than from phosphorus (P)?

Answer 26

- outer electron in S is paired with another electron - it is easier for S to lose one electron due to repulsion between paired electrons

Question 27

What is a mass spectrometer?

Answer 27

accurate scientific instrument used to determine relative isotopic mass and isotopic abundance (these values are then used to calculate RAM)

Question 28

What are the uses of mass spectrometry?

Answer 28

- carbon-14 dating - detecting illegal drugs - forensic science

Question 28

What are the 4 stages of mass spectrometry?

Answer 28

- ionisation - acceleration - ion drift in flight tube - detection

Question 29

Electrospray ionisation

Answer 29

- sample dissolved in volatile solvent and pushed through needle at high pressure - high voltage applied causing each atom to gain a proton (H^+ ion) - X (g) + H^+ --> XH^+ (g)

Question 30

Electron impact ionisation

Answer 30

- sample is vaporised - high energy electron fired at sample to knock one electron off of each particle - X (g) --> X^+ + e^-

Question 31

What happens during the 2nd step of mass spectrometry?

Answer 31

- acceleration - +vely charged ions accelerated by electric field so they all have the same Ek

Question 32

What happens during the 3rd step of mass spectrometry?

Answer 32

- ion drift in flight tube - ions enter region with no electric field so they drift - lighter ions drift faster than heavier ions therefore heavier ions take longer to reach the detector

Question 33

What happens during the 4th step of mass spectrometry?

Answer 33

- detection - ions reach detector (-ve plate) and generate a small current (produced by e^- transferring from -ve detector to +ve ions) - current size is proportional to abundance of isotope

Question 34

What is a mass spectrum?

Answer 34

plot of relative abundance against mass : charge ratio (m/z)

Question 35

How do you calculate time of flight?

Answer 35

TOF (s) = length of flight tube (m) x √ ( mass (kg) / 2 x kinetic energy (J)) t = d√(m/2Ek)