physical chem; atomic structure

Question 1

describe the history of the atom over the years

Answer 1

1803 (dalton) - atoms are spheres & each element is made up from different spheres

1897 (j.j. thompson) - discovered the e-. plum pudding model was developed

1909 (rutherford) - discovered the nucleus. gold leaf experiment

1913 (bohr) - proposed e- were in fixed energy shells

atomic model today - e- don’t have the same energy in shells, they have subshells - explains IE trends

Question 2

what was the gold leaf experiment?

Answer 2

+ve alpha particles were fired at a thin gold leaf
most went through the gold leaf - mainly empty space
a small number deflected back - they hit a small +ve nucleus

Question 3

what is the experimental proof?

Answer 3

when EM radiation is absorbed, e- move between the shells
and they emit this radiation when e- move down to lower-energy shells

Question 4

what does an atom consist of?

Answer 4

an atom consists of a nucleus containing protons & neutrons surrounded by electrons

Question 5

what are the relative charges & masses of the subatomic particles in an atom?

Answer 5

proton: rc = +1 & rm = 1
neutron: rc = 0 & rm = 1
electron: rc = -1 & rm = 1/1840

Question 6

how is the no.of neutrons calculated?

Answer 6

no.of neutrons = mass number - atomic number

Question 7

define the term ion

Answer 7

ions are atoms/molecules with a different number of protons and electrons

Question 8

define the term isotope

Answer 8

isotopes are elements with the same no.of protons & electrons but have a different no.of neutrons

Question 9

name & explain the 1st stage in the TOF mass spectrometer

Answer 9

vaporisation
sample is vaporised so it can travel through the TOF mass spec

Question 10

name & explain the 2nd stage in the TOF mass spectrometer

Answer 10

ionisation
the sample is pushed through a nozzle machine making a high pressure jet
a high voltage is passed through causing loss of e-
a gaseous +vely charged sample is produced
called electrospray ionisation

Question 11

name & explain the 3rd stage in the TOF mass spectrometer

Answer 11

acceleration
+ve ions passed through an electric field
particles with a lower mass/charge (m/z) ratios will accelerate quicker

Question 12

name & explain the 4th stage in the TOF mass spectrometer

Answer 12

ion drift
particles travel through with a constant speed & KE
they drift through & particles with lower mass/charge (m/z) ratios travel faster

Question 13

name & explain the 5th stage in the TOF mass spectrometer

Answer 13

detection
ions are detected as an electric current is made when particle hits the plate
particles with lower m/z reach detector 1st as they travel the fastest

Question 14

define relative atomic mass (Ar)?

Answer 14

it’s the average mass of an atom of an element compared to 1/12th mass of a carbon-12 atom

Question 15

define relative molecular mass (Mr)

Answer 15

it’s the average mass of a molecule compared to 1/12th mass of a carbon-12 atom

Question 16

define relative isotopic mass

Answer 16

it’s the mass of an atom of an isotope of an element compared to 1/12th mass of a carbon-12 atom

Question 17

how is relative atomic mass calculated?

Answer 17

R.A.M = ∑(isotopic mass x relative abundance) ÷ total relative abundance

Question 18

how are orbitals filled?

Answer 18

orbitals are filled singly & then pair up - due to e- repulsion

Question 19

whats the difference in removing electrons between ions & transition metals?

Answer 19

in ions e- are removed from the highest energy levels first whereas in transition metals an e- moves from the 4s to 3d orbital - to create more stable half full / full 3d subshell

Question 20

define the term ionisation energy

Answer 20

it’s the minimum amount of energy required to remove 1 mole of e- from 1 mole of atoms in the gaseous state

Question 21

does IE’s have +ve/-ve values & why

Answer 21

IE always have a +ve value as they are always an endothermic process - as they require energy

Question 22

name & describe the factors that affect IE

Answer 22

shielding - more e- shells between +ve nucleus & e- = less energy required to remove e- as there is a weaker attraction

nuclear charge - more protons in nucleus = stronger attraction between nucleus & outer e- which means more energy is required to remove e-

atomic size - the bigger the atom = the greater the distance between nucleus & outer e- so attraction gets weaker making it easier to remove e-

Question 23

define the term successive ionisation

Answer 23

it’s the removal of more than 1 e- from the same atom

Question 24

what is the IE trend for groups?

Answer 24

IE decreases down a group

Question 25

explain the reason for the IE trend for groups

Answer 25

IE decreases as:
atomic radius increases - outer e- further from nucleus = weaker attraction so less energy required to remove e-

shielding increases - more shells = weaker attraction so less energy required to remove e-

Question 26

what is the IE trend for periods?

Answer 26

IE increases across periods

Question 27

explain the reason for the IE trend for periods

Answer 27

across a period:
increasing no.of protons = increases nuclear attraction
similar shielding

more energy required to remove outer e- so IE increases

Question 28

explain the evidence for atoms having subshells

Answer 28

a decrease in Al (in period 3 IE trends)
the outermost e- sits in a higher subshell slightly further from the nucleus than in Mg making e- easier to remove than Mg

Question 29

explain the evidence for electron repulsion in orbitals

Answer 29

a decrease in sulfur (in period 3 IE trends)
P & S both have outer e- in 3p orbital so shielding is the same
removing e- from S involves taking it from orbital with 2e- = easier to remove e- as e- repel

easier to remove e- in P as there is only 1e- in the 3p orbital than S which has 2e-