2.1.1 Atomic Structure and Isotopes

Question 1

Describe the structure of an atom

Answer 1

Small, dense nucleus of protons and neutrons surrounded by electrons in energy levels.

Question 2

Subatomic particles, their masses and charges

Answer 2

Proton +1 charge, 1 relative mass
Neutron 0 charge, 1 relative mass
Electron -1 charge, 1/1840 relative mass

Question 3

Number of electrons in each shell

Answer 3

2n^2 where n is the shell
e.g. shell 1 = 2 x 1^2 = 2 electrons
shell 3 = 2 x 3^2 = 18 electrons

Question 4

Mass number and atomic number

Answer 4

Atomic number = number of protons

Mass number = number of protons + number of neutons

Question 5

definition of ion

Answer 5

When an atom gains or loses electrons
Gain of electrons = negative ion (anion)
Loss of electrons = positive ion (cation)

Question 6

Definition of isotopes

Answer 6

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

Question 7

Chemical and physical properties of isotopes

Answer 7

Same chemical properties as they have the same electron configuration.
Different physical properties due to different masses.

Question 8

Definition of relative atomic mass (Ar)

Answer 8

The weighted mean mass of an atom of an element compared to 1/12 the mass of a C-12 atom.

Question 9

Definition of relative isotopic mass

Answer 9

The weighted mean mass of an isotope compared to 1/12 the mass of a C-12 atom.

Question 10

Definition of relative molecular mass (Mr)

Answer 10

The weighted mean mass of molecule of a compound compared to 1/12 the mass of a C-12 atom.

Question 11

Difference between relative molecular mass and relative formula mass

Answer 11

relative molecular mass is used for simple molecular structures. e.g. CO2
Relative formula mass is used for giant structures e.g. giant ionic lattices NaCl

Question 12

How time of flight (TOF) mass spectrometry works

Answer 12

TOF mass spectrometry records the time it takes for ions of each isotope to reach a detector. A spectrum is produced showing each isotope present and the abundances of each isotope.

Question 13

How to calculate Ar

Answer 13

sum of (mass of each isotope x its abundance)/total abundance

Question 14

boron is analysed by TOF. It contains 2 isotopes: B-12 and B-10, where would you expect peaks and what would they represent?

Answer 14

Peak at m/z 10 for 10-B+

Peak at m/z 12 for 12-B+

Question 15

chlorine is analysed by TOF. It contains 2 isotopes: Cl-35 and B-37, where would you expect peaks and what would they represent?

Answer 15

Peak at m/z 35 for 35-Cl+
Peak at m/z 37 for 37-Cl+
Peak at m/z 70 for diatomic Cl2 + composed of 2xCl-35
Peak at m/z 72 for diatomic Cl2 + composed of 1xCl-35 and 1xCl-37
Peak at m/z 74 for diatomic Cl2 + composed of 2xCl-37

Question 16

A sample of boron contains 52% B-10 and 48% B-12 what is the Ar

Answer 16

(52x10)+(48x12)/100 = 10.96

Question 17

A sample of chlorine contains 75% Cl-35 and 25% Cl-37 what is the Ar

Answer 17

(75x35)+(25x37)/100 = 35.5