Atomic Structure

Question 1

What is the mass number?

Answer 1

The top number which tells you the protons and neutrons.

Question 2

What is the atomic number?

Answer 2

The bottom number which tells you the number of protons. (also electrons)

Question 3

Charge of Proton, Neutron and Electron:

Answer 3

P - +1

N - 0

E - -1

Question 4

Mass of Proton, Neutron and Electron:

Answer 4

P - 1

N - 1

E - 1/1860

Question 5

How many electrons can fit in the shells?

Answer 5

2,8,18

Question 6

How are protons and neutrons held together?

Answer 6

By strong nuclear forces which are stronger than electrostatic forces of attraction between the protons which overcomes the repulsion.

Question 7

What are isotopes?

Answer 7

Atoms with the same number of protons but different neutrons = different mass number.

Question 8

Do isotopes still react the same way?

Answer 8

Yes because they have the same electron configuration.

Question 9

How did the atoms develop?

5

Answer 9

Robert Boyle - said there were substances that couldn’t be simpler.

John Dalton - discovered atom

Henri Becquerel - discovered radioactivity which shows there are particles inside atoms.

• J J Thomson - plum pudding model.
• Ernest Rutherford - alpha scattering

Question 10

How did the arrangement of the electrons develop? (4)

Answer 10

• Neil Bohr, like a tiny solar system, electrons orbit nucleus.
• Erwin S electrons have same properties as waves, Quantum Mechanics discovered which predicts behaviour of sub atomic particles.
• James Ch - discovered Neutron.
• Lewis - modern ideas about bonding and how ions we’re formed.

Question 11

What is Carbon Dating?

Answer 11

It is a way to find out the age of a carbon- based material up to 60,000 years old.

Question 12

One well known radioactive carbon isotope is…

Answer 12

Carbon-14 with a half life of 5730 years and is produced by cosmic ray activity in the atmosphere.

Question 13

Does the level of Carbon-14 stay the same?

Answer 13

Yes because all living things give out and take in carbon so it stays the same. Once it dies though, the radioactive carbon breaks down and the radioactivity falls.

Question 14

Carbón-14 half life is:

Answer 14

5730.

Question 15

What do scientists use the half life for in a material which has carbon?

Answer 15

Scientists use this half life to work backwards so they work out how long it has taken for the level of radioactivity to fall from what it is in a living organism to what it is in the sample.

Question 16

What is the Mass Spectrometer?

Answer 16

The most useful instrument for the accurate determination of relative atomic masses.

Question 17

What happens in the time of flight mass spectrometer?

Answer 17

Basically the substances in the sample are converted to positive ions, accelerated to high speeds and arrive at the detector.

Question 18

The whole mass spectrometer apparatus is kept under…

Answer 18

A high vacuum to prevent the ions that are produced colliding with molecules from the air.

Question 19

What is the first stage in the time of flight mass spectrometer?

Answer 19

Ionisation. There are two types:

• electron Impact
• electro spray ionisation.

Question 20

What happens in Electron Impact?

Answer 20

The sample is vaporised and high energy electrons are fired at it from an electron gun - this knocks one electron of each particle forming a positive ion.

Question 21

What happens in Electrospray Ionisation?

Answer 21

The sample is dissolved in a volatile solvent and forced through a fine hollow needle connected to the positive terminal of a high voltage supply which produces tiny positively charged droplets.

Question 22

What is the second stage in the time of flight mass spectrometer?

Answer 22

Acceleration - the positive ions are attracted towards a a negatively charged plate and they accelerate towards it.

Question 23

Where do the ions pass through in the negatively charged plate?

Answer 23

A hole in the plate, forming a beam and they travel along this flight tube to a detector.

Question 24

What happens at the ion detector?

Answer 24

The lighter ones arrive first as they have higher velocities - flight times are recorded and the positive ions pick up an electron from the detector causing a current to flow.

Question 25

The signal from the detector is passed…

Answer 25

To a computer which generates a mass spectrum.