Physical chem I

Question 1

Define the mass number of an atom

Answer 1

The total number of protons and neutrons in an atom

Question 2

Define relative atomic mass

Answer 2

Average mass of an atom of an element/ 1/12 th mass of a C12 atom

Question 3

Give 2 reasons why it is necessary to ionise the isotopes of chromium before they can be analysed in a TOF mass spectrometer

Answer 3

Ions will be accelerated
Ions will create a current when hitting the detector

Question 4

Describe how the molecules are ionised using electrospray ionisation

Answer 4

Sample is dissolved in a volatile solvent
Passed through a thin needle connected to a high voltage, to create a fine mist
Each particle in the same gains a proton, forming a 1+ charge

Question 5

Define metallic bonding

Answer 5

Strong electrostatic attraction between positive metal ions surrounded by a sea of delocalised electrons

Question 6

Define covalent bonding

Answer 6

Shared pair of electrons between 2 atoms

Question 7

Macromolecules

Answer 7

Silicon
Silicon oxide
Carbon

Question 8

Define ionic bonding

Answer 8

Strong electrostatic attraction between oppositely charged ions

Question 9

Define coordinate bond

Answer 9

Shared electron pair, which have been donated from the same atom

Question 10

Define electronegativity

Answer 10

Power/ability of an atom to attract a pair of electrons in a covalent bond

Question 10

How does hydrogen bonding arise? H and F example

Answer 10

Large difference in electronegativity between the H and F atoms
This creates a strong dipole on the F and H bond
The lone pair of electrons on the F atom attracts the H delta+ on another molecule

Question 11

How do PDDS arise? Eg. H Cl

Answer 11

There is a difference in electronegativity between the H and Cl atoms
This creates a dipole
Dipoles don’t cancel out
Cl delta- attracts H delta+ on another molecule

Question 12

How do IDDS/VdW arise Eg. Cl2

Answer 12

Random movement of electrons
Creates an uneven distribution of electron density
This is a temporary dipole
This induces a dipole in another molecule (neighbouring molecule)
delta+ attracts delta- on another molecule

Question 13

Some of the liquid injected did not evaporate because it dripped into the gas syringe nozzle outside the oven.
Explain how this would affect the value of the Mr of Y calculated from the experimental results.

Answer 13

The volume recorded would be LOWER
Mr would be GREATER than the real Mr

Question 14

Define empirical formula

Answer 14

The simplest/lowest whole number ratio of an element in a compound/substance

Question 15

Why is the second ionisation energy of Mg less than the first ionisation energy of Ng

Answer 15

Electrons being removed from a positive ion
More energy required to remove 1 mole of electrons from mole of positive ions