atomic structure

Question 1

What is the atomic number

Answer 1

The number of protons, it defines the element

Question 2

What is the mass number

Answer 2

The protons and the neutrons

Question 3

How do you calculate the neutrons

Answer 3

Mass number - proton number

Question 4

What is the Bohr model

Answer 4

Atoms are made of three subatomic particles, protons, neutrons & electrons

E-s in shells surrounding the nucleus
Protons & neutrons in the nucleus

Question 5

What is the relative mass & charge of the following

Proton
Neutron
Electron

Answer 5

Proton - 1, +1
Neutron- 1, 0
Electron - 1/1840, -1

Question 6

Define isotope

Answer 6

Same number of protons, different number of neutrons

Question 7

What are the chemical properties of isotopes

Answer 7

Isotopes have the same chemical properties
Because they have the same electronic configuration

Question 8

What evidence was found to support Rutherfords model

Answer 8

Most of the alpha particles passed straight through the gold foil
Atoms are mainly empty space

Small number of particles bounced back
Atoms have a smalls positive nucleus

Question 9

What are the key differences between Thompson’s model & Bohr’ model

Answer 9

Bohr model has e’s surrounding nucleus in shells
Small positive nucleus

Question 10

Define ionisation energy

Answer 10

The amount of energy required to remove one mole of electron (E-s) from one mole of atoms in gaseous state

Question 11

Give the first 3 ionisation energy of Na

Answer 11

Na (g) -> Na+ (g) + E-
Na+ (g) -> Na2+ (g) + E-
Na2+ (g) -> Na3+ + E-

Question 12

What are the 3 factors that will influence ionisation energy

Answer 12

Nuclear charge, amount of protons-
More protons means a stronger attraction between the nucleus and the outer e-s
More energy is needed to remove the outer e-

Distance from the nucleus-
Outer e- is closed it the nucleus
Means there is a stronger attraction between the outer e- and nucleus
More energy needed to remove outer e-

Shielding -
More shielding
Weaker attraction between outer e- and the nucleus
Less energy needed to remove the outer e-

CONSIDER SHIELDING FIRST

Question 13

What are the trends in the first IE across a period

Answer 13

Increases across a period

Atomic radius decreases across a period
Some shielding
Increases protons -> increasing attraction between protons & outer e-s

Question 14

What is the electronic configuration for chromium

Answer 14

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

Question 15

What is the electronic configuration for copper

Answer 15

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

Question 16

Trends in ionisation energies across period 2

Answer 16

General increase in 1st IE
Shielding is the same for all atoms
Number of protons increase - increasing attraction between outer e- and nucleus

Question 17

Trends in ionisation energies in period 3

Answer 17

General increase in 1st IE
Shielding is the same for all atoms
Number of protons increase - increasing attraction between outer e- and nucleus

Question 18

How does ionisation energy change down a group

Answer 18

IE decreases down groups because
Atomic radius increases
Shielding increases
Outer e-s less attracted to nucleus

Question 19

State and explain the trend is atomic radius down a group

Answer 19

Atomic radius increases
Shielding increases
Outer e-s less attracted to nucleus

Question 20

Why does atomic radius get smaller from right to left across a period

Answer 20

Shielding stays the same
Number of protons increases
Outer electrons are more attracted to the nucleus

Question 21

How can time of flight be measured

Answer 21

T = d/v

T = d square root m/2KE

Question 22

What does KE equal
What does m equal
What does v2 equal

Answer 22

KE + 1/2 mv^2
M = KE / 1/2 v2
V2 = square root KE/ 1/2 m

Question 23

What two factors does the mass spectrometer measure

Answer 23

Relative abundance
Mass/charge ratio (m/z)

Question 24

Why are the sample particles ionised?

Answer 24

• So they can be accelerated towards the negatively charged plate
• So they generate a current when they hit the detector

Question 25

How is the ion accelerated?

Answer 25

•Positive ions attracted to the negatively charged plate
• All ions have the same kinetic energy

Question 26

How are ions separated in the flight tube?

Answer 26

• lons travelling at higher speeds (small m/z) move ahead of those travelling more slowly (large m/z)

Question 27

How are the ions detected?

Answer 27

• Each ions hits the detector
• Ion gains an electron
• Generates a current
• Size of the current is proportional to the abundance of the ion

Question 28

What is the formula for electron impact

Answer 28

X(g) —> X+ (g) + e-

Question 29

What is the equation for electro spray ionisation

Answer 29

H+ —> XH+

Question 30

Describe electrospray ionisation

Answer 30

The sample X is dissolved in a volatile solvent (eg water or methanol) and injected through a fine hypodermic needle to give a fine mist (aerosol). The tip of the needle is attached to the positive terminal of a high-voltage power supply.

The particles are ionised by gaining a proton (ie an H + ion which is simply one proton) from the solvent as they leave the needle producing XH* ions (ions with a single positive charge and a mass of Mr + 1).

Question 31

Describe electron impact

Answer 31

The sample being analysed is vaporised and then high energy electrons are fired at it.

The high energy electrons come from an ‘electron gun’ which is a hot wire filament with a current running through it that emits electrons.

This usually knocks off one electron from each particle forming a 1+ ion