Atomic Structure

Question 1

What does an atom consist of? Charges and masses?

Answer 1

Electrons - negative charge, mass of 1/1840
Protons - positive charge, mass of 1
Neutrons - no charge, mass of 1
Nucleus with protons and neutrons in, electrons in shells

Question 2

The evolution of the atom

Answer 2

Thomson - discovered the electron (plum pudding model - positively charged ball with electrons dotted in)
Rutherford - electrons orbit with most of the mass concentrated in the nucleus (alpha particle test)
Bohr - electrons move in orbits

Question 3

What is an isotope?

Answer 3

Element with same proton number, different number of neutrons

Question 4

Time of Flight Spectrometer Method

Answer 4

Sample injected with a hypodermic needle
Ionisation
Acceleration
Separation
Detector

Question 5

TOF - Electron Impact Ionisation

Answer 5

Used for elements/substances with a low Mr
Shoot high energy electrons from an electron gun at the sample
It knocks of an electron - forming a 1+ ion
It is random so often breaks down into fragments that get detected on the spectrum

Question 6

TOF Electron Impact Ionisation Equation

Answer 6

X(g) + e- —> X+ (g) + 2e-
Or
CH4 (g) + e- —> CH4+ (g) + 2e-

Question 7

TOF - electrospray ionisation

Answer 7

Used for high Mr molecules/elements
Rarely gives fragments
Sample is dissolved in a volatile solvent
Injected with the hypodermic needle
Tip of needle has a voltage applied to it
Each molecule gains a H+ proton

Question 8

TOF electrospray ionisation equation

Answer 8

M (g) + H+ —> MH+ (g)

Question 9

TOF -acceleration of ions

Answer 9

1+ ions are accelerating using an electric field (negatively charged plate)
So all the ions have the same kinetic energy (Ek)
Formula - Ek = 1/2mv^2

Question 10

TOF - separation of ions

Answer 10

Positive ions travel through a hole in the negative plate into the flight tube
TOF of each particle depends on its velocity (and hence its mass)
d = vt

Question 11

TOF - detection

Answer 11

Detector is a negatively charged plate (ions gain e-)
This generates a current
The size of current is proportional to the abundance of isotopes

Question 12

Relative atomic mass equation (using abundance)

Answer 12

(Mass x abundance) + (mass x abundance) / total abundance

Question 13

TOF calculations

Answer 13

To find mass - Ar / L (Avogadro’s Constant) / 1000 to get it into kg
To find velocity - rearrange equation using the mass you just found
To find distance - use the velocity you just found x time (in metres)

Question 14

Mass spectra

Answer 14

Chlorine ratio = Cl35 (75%) and Cl37 (25%)
Bromine ratio = Br79 (50%) and Br81 (50%)
Find the possible outcomes which reflect the ratios
The more abundant the isotope is, the higher the peak is

Question 15

How to predict the appearance of mass spectra for diatomic molecules

Answer 15

Make the isotopes into a ratio
Change the ratio into fraction form
Calculate the possibilities of combinations by MULTIPLYING the fractions together
Add together any that have 2 possibilities
Simplify back into a ration (can be decimal or percentage)

Question 16

What are the 4 sub shells and how many electrons can be held in each

Answer 16

S = 2
P = 6
D = 10
F = 14

Question 17

How to remember the filling order for electron configuration

Answer 17

4S is filled before 3D
This is because 4S has lower energy
1
2s 2p
3s 3p 3d
4s 4p 4d 4f

Question 18

Short structure + how electrons fill up in electron configuration

Answer 18

Electrons prefer to be on their own in the orbitals, however do pair up when no or orbitals left of the same energy
Short structure - use the noble gas before the element and then rest of structure
E.g 1s2 2s2 2p5 = [He] 2s2 2p5

Question 19

Electron configuration - pesky transition metals

Answer 19

Chromium = 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Promoted 1 e- to 3d, both have half filled sub-levels
Copper = 4s1 3d10
One half filled and one full

Question 20

What is it called when electrons have the same configuration?

Answer 20

Isoelectronic species

Question 21

As you go down a group, why does the atomic radius increase?

Answer 21

More electron shells/shielding
Has a weaker attraction between the nucleus and the outer electrons

Question 22

As you go across a period, why does the atomic radius decrease?

Answer 22

Electrons are in the same shell (same shielding)
Therefore, there is a stronger attraction between the nucleus and the outer electrons
More protons means bigger nuclear charge (pulling electrons closer)

Question 23

Definition of first ionisation energy

Answer 23

Enthalpy change required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

Question 24

Example of ionisation energy equations

Answer 24

1st Na (g) —> Na+ (g) + e-
2nd Na+ (g) —> Na2+ (g) + e-

Question 25

What 3 factors affect the first ionisation energy

Answer 25

Distance from the nucleus (atomic radius)
The closer the electron being removed to the nucleus, the stronger the attraction between the nucleus and the outer electron

Nuclear charge
The more protons, the stronger the attraction is between the nucleus and the electron being removed

Shielding
The less inner shells of electron shielding, the stronger the attraction between the nucleus and the outer electron
Less shielding = higher ionisation energy

Question 26

As you go down a group, what happens to the ionisation energy and why?

Answer 26

Ionisation energy decreases

Why =
More electron shielding meaning more full electron inner shells
Larger atomic radius - electron being removed is further from the nucleus
Means a weaker attraction between the nucleus and the electron being removed

Question 27

As you go across a period, what happens to the ionisation energy and why?

Answer 27

The ionisation energy increases

Why =
Same shielding
Increase in nuclear charge
Smaller atomic radius so stronger attraction between the nucleus and electron being removed

Question 28

Deviation in the ionisation energy across a period

Answer 28

Dip from group 2 to 3
Electron is removed from the 3p orbital
It is slightly further away from the nucleus ( + higher energy)

Dip from group 5 to 6
A pair of electrons in the 3p orbital which REPEL each other