Atomic Structure

Question 0

Define the term mass number of an atom.

Answer 0

The number of protons and neutrons in the nucleus.

Question 1

Define the term relative atomic mass of an element.

Answer 1

Ar = average mass per atom of an element x 12 / mass of one atom of carbon - 12

Question 2

Define the term atomic number of an atom.

Answer 2

The number of protons in the nucleus of an atom.

Question 3

In terms of fundamental particles, state the difference between isotopes of an element.

Answer 3

Different number of neutrons.

Question 4

State why isotopes of an element have the same chemical properties.

Answer 4

Same number of electrons.

Question 5

Suggest one reason why particles with the same mass and velocity can be deflected by different amounts in the same magnetic field.

Answer 5

The deflection of an ion depends on the ratio of its mass to charge (m/z).

Question 6

Explain how the detector in a mass spectrometer enables the abundance of an isotope to be measured.

Answer 6

Ions hit the detector and cause current to flow. Bigger current = More of the isotope.

Question 7

Name the four key stages in the separation of isotopes (Mass Spectrometer).

Answer 7

Ionisation
Acceleration
Deflection
Detection

Question 8

Equation for Mass Spectrometer?

Answer 8

X(g) ➕ e- ➡️ X+ ➕ 2e-

Question 9

Isotopes of tungsten include 182W and 186W.

i) Deduce the number of protons in 182W.
ii) Deduce the number of neutrons in 186W.

Answer 9

i) 74

ii) 112

Question 10

Give two reasons why the sample must be ionised. (Mass Spectrometer)

Answer 10

To accelerate it.

To deflect it.

Question 11

State what can be adjusted in the mass spectrometer to enable ions formed by the different isotopes to be directed onto the detector.

Answer 11

Strength of the magnetic field.

Question 12

Vaporisation?

Answer 12

The sample is turned into gas using an electrical heater.

Question 13

Ionisation?

Answer 13

The sample is bombarded with electrons using an electron gun. This knocks out another electron so that positive ions (cations) are produced.

Question 14

Acceleration?

Answer 14

The positive ions (cations) are accelerated by an electric field. Ions move towards the negative plate and are focused into a beam by slits.

Question 15

Deflection?

Answer 15

The positive ions’ paths are altered with a magnetic field. Lighter ions have less momentum and are deflected more than heavier ions.

Question 16

Detection?

Answer 16

The magnetic field strength is slowly increased. Ions hit the detector, accept electrons, lose their charge and create a current.

A computer works out the value of the mass to charge ratio (m/z), of the original ion. A graph: relative abundance of ions against mass to charge ratio (m/z).

Question 17

Define the term relative molecular mass.

Answer 17

Mr = average (mean) mass of the compound x 12 / mass of one atom of carbon - 12

Question 18

Electronic Configuration of Chromium (Cr)?

Answer 18

1s(2), 2s(2), 2p(6), 3s(2), 3p(6), 3d(5), 4s(1)

Question 19

Electronic Configuration of Copper (Cu)?

Answer 19

1s(2), 2s(2), 2p(6), 3s(2), 3p(6), 3d(10), 4s(1)

Question 20

Electronic Configuration of Fe(3+)?

Answer 20

1s(2), 2s(2), 2p(6), 3s(2), 3p(6), 3d(5)

Question 21

Electronic Configuration of Cl-?

Answer 21

1s(2), 2s(2), 2p(6), 3s(2), 3p(6)

Question 22

Cation?

Answer 22

A positively charged ion.

Question 23

Anion?

Answer 23

A negatively charged ion.

Question 24

State what is used to accelerate ions in a mass spectrometer.

Answer 24

An electric field.

Question 25

State what is used to deflect ions in a mass spectrometer.

Answer 25

A magnetic field.