3.1.1 Atomic Structure

Question 1

Dalton and Thomson Models

Answer 1

19th century Dalton - Atoms are spheres, different spheres make up different elements.
Thomson - atoms contains electrons
‘plum pudding model’

Question 2

Rutherford’s model

Answer 2

Gold foil experiment, fired alpha particles at gold foil.
Most particles passed straight through, very small number reflected backwards.
Nuclear model.
Mostly empty space, positive central nucleus and random electrons in empty space
Problem: cloud of electrons would spiral down into nucleus.

Question 3

Bohr’s model

Answer 3

Electrons only exist in fixed orbitals with fixed energy levels.
When electrons move between shells electromagnetic radiation is emitted or absorbed.
Level of radiation has a fixed frequency.
Later changed to include sub-shells.

Question 4

Sub-atomic particles relative charge

Answer 4

Proton +1
Neutron 0
Electron -1

Question 5

Sub-atomic particles relative mass

Answer 5

Proton +1
Neutron +1
Electron 1/2000

Question 6

The structure of the atom

Answer 6

All elements are made of atoms.

Atoms contain protons and neutron in a nucleus and orbiting electrons in fixed energy levels (shells)

Question 7

Mass number

Answer 7

A - number of protons and neutrons

Question 8

Atomic number

Answer 8

Z - number of protons.

Question 9

Isotopes

Answer 9

Different atoms of the same element, same number of protons, different number of neutrons.
In general have same chemical reactivity as same electronic configuration.

Question 10

Purpose of a mass spectrometer

Answer 10

Find relative atomic mass by identifying the mass and abundance of isotopes in a sample.
Finding the relative molecular mass of a substance made of molecules.
Identify elements

Question 11

Electrospray ionisation

Answer 11

sample is dissolved in a volatile solvent
injected through a fine hypodermic needle to give a fine mist
attached to the positive terminal of a high voltage power supply.
Gains a proton (mass number increases by one)
One plus ion.

Question 12

Electrospray ionisation Equation

Answer 12

X(g) + H+ —> XH+(g)

Question 13

Electron impact ionisation

Answer 13

Sample is vaporised
High energy electrons are fired at it from an electron gun
Knocks off one electron to form a one plus ion

Question 14

Electron impact ionisation Equation

Answer 14

X(g) + e- —–> X+(g) + 2e-

Question 15

When is electron impact ionisation used?

Answer 15

Elements and substances with low formula mass

Question 16

When is electrospray ionisation used?

Answer 16

Substances with a high molecular mass.

Biological molecules such as proteins.

Question 17

Acceleration (TOF)

Answer 17

Ions are attracted towards a negative plate where they are accelerated.
Have the same Kinetic energy.
Uses an electric field

Question 18

Kinetic energy equation and units

Answer 18

KE = 0.5 x m x v2
KE joules
m Kilograms
v meters per second

Question 19

Flight tube (TOF)

Answer 19

Positive ions travel through a hole in a negatively charged plate.
Travel through flight tube.
As all have same kinetic energy are separated by mass, lightest ions travel the fastest.

Question 20

Speed distance time equation and units.

Answer 20

Speed = distance / time
Speed meters per second
Distance meters
Time seconds

Question 21

Detector (TOF)

Answer 21

Lightest ions travel the fastest so take the less time to reach the detector.
Positive ions hit a negatively charged plate.
Discharged by gaining an electron from the plate.
Movement of charge generates a current.
Size of current is proportional to the abundance.

Question 22

Mass spectrum tips

Electrospray ionisation

Answer 22

Molecular ion is highest peak to the right
Smaller peaks to the left are due to fragmentation
Surrounding peaks are because of isotopes.
Remove one from the molecular ion due to mass of added proton.

Question 23

Mass spectrum tips

Electron impact ionisation

Answer 23

Smaller peaks due to different ion eg (2+) efecting mass charge ratio on the x axis.
Height of peaks proportional to abundance of ion.

Question 24

Relative molecular mass

Answer 24

The average mass of one molecule relative to one twelfth the mass of one molecular of carbon twelve.

Question 25

How to calculate relative molecular mass?

Answer 25

total abundance

Question 26

maths tips for time of flight

Answer 26

Divide mass number by 1000 to get in Kg for KE equation.
Divide mass number by Avogadro’s constant for the mass of one ion for KE equation.
m1/t1 = m2/t2

Question 27

Electron configuration order

Answer 27

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

4s fills and empties before 3d

Question 28

Copper electronic configuration

Answer 28

1s2 2s2 2p6 3s2 3p6 4s1 3d10

Question 29

Chromium electronic configuration

Answer 29

1s2 2s2 2p6 3s2 3p6 4s1 3d5

Question 30

Ionisation energy

Answer 30

The minimum amount of energy required to remove one mole of electrons from one mole of gaseous ions to form one mole of gaseous one plus ions.

Question 31

Ionisation energy equations

First and second

Answer 31

X(g) —-> X+(g) + e-

X+(g) —–> X2+(g) + e-

Question 32

Why is the second ionisation energy higher than the first?

Answer 32

Electron is removed from a more positive species, stronger nuclear charge.

Question 33

Electron configuration with arrows

Answer 33

Two arrows in one box
Each box equals an orbital
Each arrow equals an electron
All boxes in one sub shell are singly occupied first then singly occupied.
Lower energy subshells are filled first
Arrows in the same box must have opposite spins.

Question 34

Shortened electron configuration

Answer 34

Gives symbol of closest natural gas in square brackets then continues configuration

Question 35

Factors effecting ionisation energy

Answer 35

Nuclear charge
Distance from the nucleus
Shielding
Alters force of attraction between the nucleus and outer electron

Question 36

Ionisation energy across group 2

Answer 36

Decreases
Larger atomic radius/ more shells
More shielding
Weaker force of attraction between the nucleus and outer electron.

Question 37

Ionisation energy across a period

Answer 37

Increases
Smaller atomic radius
Similar shielding
More protons/ stronger nuclear force
Stronger force of attraction between the nucleus and outer electron.

Question 38

Change in ionisation energy between group 2 and group 3

Answer 38

Move from s to p orbital
Higher energy level
Weaker force of attraction between the nucleus and outer electron

Question 39

Change in ionisation energy between group 5 and group 6

Answer 39

Change from p3 to p4 orbital.
Orbital is now doubly occupied.
Increases electron-electron repulsion.

Question 40

Identifying group of element from ionisation energy graph

Answer 40

Count the number of electrons removed with only small increases between energy. Stop before big increase.
This is the number of electrons in the outer shell so is the group number.