Ch4 Relative Tomic Mass, Isotopes, Mass Spectrometry

Question 1

Isotopes

Answer 1

Atoms of the same element (same atomic number) but different mass number due to the different number of neutrons in the nucleus.

Question 2

Who built the mass spectrometer and what does it do

Answer 2

Francis William Aston
Measure masses of atoms

Question 3

What did Aston find with neon

Answer 3

Neon gas had two types of atoms one with mass 20, one with mass 22

Concluded that neon gas consisted of atoms with different numbers of neutrons in the nucleus

Question 4

What did Aston also determine

Answer 4

Determined the percentages of the isotopes in a typical sample of these elements

Question 5

How to find avg mass of cl

Answer 5

1.Multiple percentage by mass number for both isotopes

2. Add answers together (100atoms mass)
3. Divide by 100

Question 6

Relative atomic mass

Answer 6

The average of the mass numbers of the isotopes of the element,
As they occur naturally
Taking their abundance into account
And expressed in a scale in which the atoms of the carbon 12 isotope have a mass of exactly 12 units

Question 7

What units does realtive atomic mass have

Answer 7

lol none

Question 8

Positive ion

Answer 8

Cation

Question 9

Negative ion

Answer 9

Anion

Question 10

How many electrons does 17 cl- have

Answer 10

18

Question 11

How many electrons does 12 mg 2+ have

Answer 11

10

Question 12

Uses of a mass spectrometer

Answer 12

-Identify presence of isotopes
-measure relative abundance
-measure relative atomic mass of an element

Question 13

Name the 5 stages of mass spectrometry

Answer 13

1. Vaporisation
2. Ionisation
3. Acceleration
4. Serparation unit in a magnetic field/ deflection
5. Detection

Question 14

Vaporistation

Answer 14

A small amount of gas or liquid is injected in the sample inlet
A vacuum is inside so liquid turns to gas
If a liquid is injected into the sample inlet, it will be vaporised into a gas using the vacuum.

Question 15

Ionisation

Answer 15

atoms or molecules are turned into ions using electric gun (in the ionisation chamber)
-a heated filament that gives off electrons-
These electrons are fired at a sample and knock out electrons from the sample’s particles to produce Positive ions.

Question 16

Why is a vacuum needed inside the spectrometer

Answer 16

So the particles can move along without colliding with any air molecules

Question 17

Accelerator

Answer 17

Positive ions produces pass between series of negatively charged plates.
-positive ions in the ionisation chamber are attracted to the negative plates and are accelerated

A fine beam of ions then passes into the analyser

Question 18

Separation unit - magnetic field

Answer 18

In the analyser, the particles are mad to move in a curved path using a magne tic field.

• lighter particles are easier to deflect than heavier ones
• lighter ones are pushed further off course than heavier

Ions are separated according to their masses

Question 19

Detector

Answer 19

Responds to the number of ions hitting it

-by changing strength of magnetic field, the operator brings ions of diff masses to focus on the detector
- signal is amplified into an electric current and viewed on a computer screen and sent to a recorder.

Question 20

Mass of one atom of an element

Answer 20

1/12 mass of one atom of carbon -12

Question 21

How many electrons can s, p , d sub levels hold

Answer 21

S - 2 ē

P - 6 ē

d - 10 ē

Question 22

Aufbau principle

Answer 22

States that when building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level.

Question 23

Pauli exclusion principle

Answer 23

No more than 2 electrons may occupy an orbital and they must have opposite spin.

Question 24

Hands rule of maximum multiplicity

Answer 24

When 2 or more orbitals of equal energy are available, electrons will electrons occuoy them singly before filling them in pairs

Question 25

Two exceptions and give their electronic configurations.

Answer 25

Cu 29 copper 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10,
Cr 24 chromium 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5