atomic structure & amount of substance

Question 1

Define relative atomic mass.

Answer 1

Relative atomic mass is the average mass of an atom on a scale where an atom of carbon 12 is 12.

Question 2

Define relative molecular mass.

Answer 2

Relative molecular mass is the average mass of a molecule on a scale where an atom of carbon 12 is 12.

Question 3

Define relative isotopic mass.

Answer 3

Relative isotopic mass is the mass of an isotope on a scale where an atom of carbon 12 is 12.

Question 4

How can relative mass be measured?

Answer 4

Relative mass can be measured with a mass spectrometer.

Question 5

What are the stages of mass spectrometry?

Answer 5

1. Ionisation (electrospray or electron impact)
2. Acceleration
3. Ion drift
4. Detection.

Question 6

What does a mass spectrum plot?

Answer 6

Mass/charge against abundance.

Question 7

How can mass spectrometry be used to identify elements?

Question 8

How do you work out relative atomic mass from a mass spectrum

Question 9

What is ionisation?

Answer 9

Ionisation is the removal of one or more electrons.

Question 10

Define first ionisation energy.

Answer 10

First ionisation energy is the energy needed to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 11

Give and explain three factors that affect ionisation energy.

Answer 11

Nuclear charge: the more protons there are in the nucleus, the more positively charged it is and the harder it is for the atom to lose electrons due to the stronger attraction.
Distance from nucleus: Attraction lowers rapidly with distance.
Shielding. As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction towards the nuclear charge.

Question 12

Define second ionisation energy.

Answer 12

Second ionisation energy is the energy needed to remove one electron from each atom in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions.

Question 13

Give the second ionisation energy of Mg.

Answer 13

Mg+(g) → e− + Mg 2+(g)

Question 14

How does first ionisation energy change down a group and why?

Answer 14

First ionisation energy decreases down group 2 because of increased shielding and distance from the nucleus.,

Question 15

How does first ionisation energy change across a period and why?

Answer 15

First ionisation energy increases across period 3 due to increasing numbers of protons and lack of extra shielding

Question 16

What is pressure measured in in pV = nRT?

Answer 16

Pa (pascal)

Question 17

What is volume measured in in pV = nRT?

Answer 17

m³

Question 18

What is R in pV = nRT?

Answer 18

8.31 J K⁻¹ mol⁻¹

Question 19

What is temperature measured in in pV = nRT?

Answer 19

K

Question 20

What is the equation for percentage yield?

Question 21

What is the equation for atom economy?

Question 22

What is the mass of an electron?

Answer 22

1/2000

Question 23

What is an isotope?

Answer 23

An isotope is an atom of an element with a different number of neutrons.

Question 24

Describe John Dalton’s model of the atom.

Answer 24

Dalton describes atoms as small, indivisible, solid spheres.

Question 25

Describe J.J Thompson's model of the atom.

Answer 25

J.J. Thompson theorised that the atom was like a plum pudding: the atom was a sphere of positive charge, with negative electrons dotted randomly throughout, like the plums in a pudding.

Question 26

Describe Ernst Rutherford's gold foil experiment and the model of the atom that it led to.

Answer 26

Rutherford fired positively charged alpha particles at a thin sheet of gold. The plum pudding model suggested that most alpha particles would be slightly deflected by the positive 'pudding'. However, most particles passed straight through the foil, and only a very small amount were deflected. This led Rutherford to develop the nuclear model of the atom, in which the nucleus of the atom is tiny and surrounded by a cloud of electrons, meaning most of the atom is empty space.

Question 27

Describe Bohr's model of the atom.

Answer 27

Bohr theorised that electrons in a 'cloud' around the nucleus would be attracted towards it due to opposite charges, so he proposed a model of the atom in which electrons orbit the nucleus in energy levels, or 'shells'