3.1.1 Atomic Structure

Question 1

Purpose of a mass spectrometer:

Answer 1

To measure the mass of atoms and molecules very accurately

Question 2

What did Robert Boyle do?

Answer 2

Put forward the idea that certain substances could not be broken down further (1661)

Question 3

What did John Dalton do?

Answer 3

Suggested that elements were atoms which could not be broken down.
Atoms of the same element had the same mass but different to atoms of other elements.
(1803)

Question 4

What did Henri Bequerel discover?

Answer 4

Radioactivity (1896)

Question 5

What did JJ Thomson do?

Answer 5

Discovered the electron and showed it was negatively charged (1897)

Question 6

What did Ernest Rutherford do?

Answer 6

Showed that most of the mass and positive charge was in the nucleus (1911)

Question 7

What did Niels Bohr do?

Answer 7

Suggested that atoms consisted of of a tiny positive nucleus orbited by negatively charged electrons (1913)

Question 8

Who was Schrödinger?

Answer 8

Developed the Quantum Theory which could be used to predict the behaviour of subatomic particles. (1932)

Question 9

Relative mass of an electron?

Answer 9

1 / 1840

Question 10

Symbol for mass number:

Answer 10

A

Question 11

Symbol for atomic number:

Answer 11

Z

Question 12

Mass number:

Answer 12

Total number of protons and neutrons in the nucleus of an atom

Question 13

What are isotopes?

Answer 13

Atoms of the same element with the same number of protons but different numbers of neutrons (different mass number)

Question 14

Relative atomic mass:

Answer 14

The average mass of an atom of an element on a scale where an atom of Carbon-12 has a mass of exactly 12

Question 15

Uses of mass spectrometer:

Answer 15

-Gives accurate information about relative atomic mass
-Gives accurate information about the relative abundance of isotopes
-Used to identify elements
Determines relative molecular masses

Question 16

Time of Flight Mass Spectrometer

Answer 16

-Particles are ionised to form 1+ ions
-Ions are accelerated so they all have the same kinetic energy
-Time taken to travel a fixed distance is used to find each ion’s mass

Question 17

Electron impact

Answer 17

-Sample is vaporised
-High energy electrons fired at sample from an electron gun
-Results in loss of an electron, forming a 1+ ion
-Ions are then attracted to a negative electric plate where they are accelerated

Question 18

When is electron impact used

Answer 18

Elements with low formula masses

If a molecule is ionised in this way, its called the molecular ion

Question 19

Electrospray ionisation

Answer 19

-Sample is dissolved in a volatile polar solvent
-Sample is injected through a fine hypodermic needle at high voltage to produce a fine mist
-Particles are ionised by gaining a proton from the solvent as they leave the needle producing XH+ ions
-Solvent evaporates away while ions are attracted to negative plate and accelerated
-Positive ions travel through a hole in the negatively charged plate into a tube, velocity is calculated
-Positive ions are discharged by gaining electrons from the negative plate
-This generates a movement of electrons - size of current measures number of ions hitting the plate

Question 20

When is electrospray ionisation used?

Answer 20

For substances with higher molecular masses (eg biological molecules such as proteins)

Question 21

Advantage of electrospray ionisation

Answer 21

Fragmentation rarely takes place

Question 22

Equation for kinetic energy:

Answer 22

1/2 x m x v^2

Question 23

Velocity equation for particles in mass spectrometer

Answer 23

V = root (2KE / m)

Question 24

Interpreting a mass spectrum

Answer 24

For elements, each line represents a different isotope of the element

Question 25

Name the sub shells

Answer 25

S
P
D
F

Question 26

Describe sub shell s

Answer 26

1 orbital
2 electrons

Question 27

Describe sub shell p

Answer 27

3 orbitals
6 electrons

Question 28

Describe sub shell d

Answer 28

5 orbitals
10 electrons

Question 29

Describe sub shell f

Answer 29

7 orbitals
14 electrons

Question 30

Rule when electrons are lost to form ions:

Answer 30

Lost from the 4s orbital before the 3d

Question 31

Ionisation energy

Answer 31

The amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous phase

Question 32

What does a high ionisation energy mean

Answer 32

That there is a strong attraction between the electron and the nucleus so more energy is needed to remove the electron

Question 33

Why does nuclear charge affect ionisation energy

Answer 33

The more protons the nucleus contains, the stronger the positive charge and the stronger the attraction to the electrons

Question 34

Why does distance from the nucleus affect ionisation energies

Answer 34

The greater the distance from the nucleus of the electron, the weaker the attraction and the lower the activation energy

Question 35

What is the shielding effect

Answer 35

As number of electron shells increases, outer shell electrons are less attracted to nucleus
This decreases ionisation energy

Question 36

Ionisation trends down group 2

Answer 36

Going down , each element has one more electron shell than the one above, so gets bigger
This extra shell shields the outer electrons from nucleus, and is not compensated for by an increase in the number of protons in the nucleus
Therefore attraction is weaker and so ionisation energy values decrease going down the group

THIS PROVIDES EVIDENCE THAT ELECTRON SHELLS EXIST

Question 37

Ionisation trends across period 3

Answer 37

General trend is that IE increases due to increase in number of protons and similar shielding

EXCEPT Mg to Al and P to S

Aluminium:

Outer shell electron is in 3p orbital , easier to remove

Sulfur:

Electron is being removed from a double occupied orbital, more repulsion, less energy needed

THUS, provides evidence for the existence of sub shells