Atomic structure

Question 1

where are protons, neutrons and electrons located in an atom ?

Answer 1

protons and neutrons are located in the middle of the atom (nucleus)

electrons occupy energy levels/ shells that orbit the nucleus

Question 2

what is the atomic number ?

Answer 2

the number of protons (and electrons) in an atom of an element
normally the smaller number

Question 3

what is the mass number ?

Answer 3

this is the amount of protons and neutrons combined

Question 4

when can an ion be positive or negative?

Answer 4

positive = protons > electrons

negative = protons < electrons

Question 5

what is an isotope ?

Answer 5

isotopes are atoms with the same number of protons and a different amount of neutrons

Question 6

what is evidence to support Rutherford’s model ?

and why is Neil Bohr’s model have shells ?

Answer 6

at point P most alpha particles were detected so he concluded atom is mostly made out of open space

at point Q 1 out of 8000 alpha particles was detected which he concluded particle was repelled by a small-dense, positive nucleus

Neil Bohr’s model having shells comes from measuring ionisation energies

Question 7

what’s the definition for ionisation energy ?

Answer 7

ionisation energy is the amount of energy needed to remove a mole of electrons from a mole of atoms in the gaseous state

e.g,

C (g) ——> C+ (g) + e-

Question 8

three factors which effect ionisation energy ?

Answer 8

1) nuclear charge (number of protons)
2) distance from nucleus
3) sheilding

Question 9

electron shells

Answer 9

s = 2e-
p = 6e-
d = 10e-
f = 14e-

Question 10

what goes before the d sub shell

Answer 10

4s2 comes before 3d10

1s2 2s2 2p6 3s2 3p6 4s2 3d10

Question 11

why is it easier to remove an electron in the P subshell compared to the S subshell when there’s only one electron in the P subshell

Answer 11

p subshell is higher in energy which makes it easier to remove an electron

Question 12

why is it easier to remove an electron from a paired P subshell compared to a P subshell with an unpaired electron

Answer 12

because electrons in a paired subshell repel making it easier for an electron to be removed

Question 13

which two anomalies are in the 4s2 3d10 subshells

Answer 13

1) chromium
should be - 1s2 2s2 2p6 3s2 3p6 4s2 3d4
is actually - 1s2 2s2 2p6 3s2 3p6 4s1 3d5
thus making it more stable

2)copper
should be - 1s2 2s2 2p6 3s2 3p6 4s2 3d9
is actually - 1s2 2s2 2p6 3s2 3p6 4s1 3d10
thus making it more stable

Question 14

how does the ionisation energy change down a group ?

Answer 14

atoms get bigger
more shielding
weaker attraction from nucleus to electron in outer shell
ionisation energy decreases down the group

Question 15

trends going across group 2 and 3

Answer 15

generally increases in ionisation energy going across the groups
as you go across - the nuclear charge increase
they have the same shielding
so a greater attraction between the nucleus and the outer electron

Question 16

why are sample particles ionised ?

Answer 16

so they can accelerate towards the negatively charged plate
so they can generate a current when they hit the detector

Question 17

how is the ion accelerated ?

Answer 17

positive ion attracted to negative plate
all ions have the same kinetic energy

Question 18

how are ions separated in the flight tube ?

Answer 18

ions travelling at higher speeds have a smaller mass
ions travelling at slower speeds have a higher mass

Question 19

how are ions detected ?

Answer 19

each ion hits the detector
ion gains an electron
generates a current
size of the current is proportional to the abundance of the ion

Question 20

electrospray ionisation

Answer 20

1) the sample is dissolved in a volatile solvent
2) The solvent is injected using a hypodermic needle producing a fine mist
3) The needle is attached to a high voltage power supply, so as the sample is injected
4) the particles are ionised by gaining a proton from the solvent
X (g) + H+ → XH+ (g)

5) The solvent evaporates and the XH+ ions are attracted towards a negatively charged plate
This accelerates them through the mass spectrometer

1) sample dissolved in volatile solvent
2) injected through a fine hypodermic needle giving a fine mist
3) tip of needle has high voltage
4) each gains a proton as it leaves the needle

Question 21

electron impact

Answer 21

1) The sample being analysed is vaporised and then high energy electrons are fired at it.
2) The high energy electrons come from an ‘electron gun’ which is a hot wire filament with a current running through it that emits electrons.
3) This usually knocks off one electron from each
particle forming a 1+ ion.
X(g) ——> X+(g) + e-

4) The 1+ ions are then attracted towards a negative electric plate where they are accelerated.

1) high energy electrons
2) from electron gun
3) fired at sample
4) knocks of one electron

Question 22

learn Ar - abundance - KE

Answer 22

from the booklet and questions

Question 23

how TOF works

Answer 23

vacuum
ionisation
acceleration
ion drift
detection
data analysis

Question 24

what happens to the 4s2 sub shell first and then the 3d10 subshell ?

Answer 24

the 4s2 subshell gains and looses electrons first and then the 3d10 subshell does

Question 25

main 4 you need to know

Answer 25

ionisation
acceleration
ion drift
detection

Question 26

This prevents particles colliding with other particles and affecting their time of flight →

Sample particles are ionised so that they can receive an electron →

Proportional to current →

The same for all ions after acceleration →

Sample particles are ionised so that they are attracted to the negative plate →

Larger ions travel slower →

Answer 26

→ Vacuum in flight tube,

→ Detection,

→ Abundance,

→ Kinetic energy,

→ Acceleration,

→ Ions separate during ion drift