Atomic structure

Question 1

atomic number

Answer 1

Z, The number of protons in the nucleus

Question 2

Mass number

Answer 2

A is the total number of protons and neutrons in the atom

Question 3

Number of neutrons

Answer 3

= A-Z

Question 4

Isotopes

Answer 4

Isotopes are atoms with the same number of protons, but different number of neutrons

Question 5

Isotopes have similar,

Answer 5

chemical properties because they have the same electronic structure

Question 6

They may have slightly varying..

Answer 6

physical properties because they have different masses

Question 7

What does the mass spectrometer determine,

Answer 7

All the isotopes present in a sample of an element and to therefore identify elements

Question 8

Why does it need to be kept under a vacuum

Answer 8

Air particles would ionise and register on the detector

Question 9

Ionisation - electron impact

Answer 9

• a vaporised sample is injected at low pressure
• an electron gun fires high energy electrons at the sample
• this knocks out an outer electron
• forming positive ions with different charges

Question 10

Ionisation - electro spray ionisation

Answer 10

• The sample is dissolved in a volatile, polar solvent
• Injected through a fine needle giving a fine mist or aerosol
• the tip of needle has high voltage
• at the tip of the needle the sample molecule, M gains a proton - forms MH+
• The solvent evaporates away while the MH+ ions move towards a negative plate

Question 11

Why is electro spray ionisation is preferably used

Answer 11

• larger organic molecules
• the softer conditions of this mean fragmentation does not occur

Question 12

Acceleration

Answer 12

• positive ions are accelerated by an electric field
• to a constant kinetic energy
  Ke = 1/2mvsquare
  rearranged v= root 2Ke/m

Question 13

Flight tube

Answer 13

• The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster
• The heavier particles take longer to move through the drift area
• the ions are distinguished by different flight times
• t=d/v

Question 14

Detection

Answer 14

• The ions reach the detector and generate a small current, which is fed into a computer for analysis.
• The current is produced by electrons transferring from the detector to the positive ions.
• The size of the current is proportional to the abundance of the species

Question 15

For each isotope the mass spectrometer can measure a …

Answer 15

m/z and an abundance

Question 16

R.A.M

Answer 16

isotopic mass X % abundance / 100

Question 17

Sub energy levels are -

Answer 17

s - 2 electrons
p - 6 electrons
d - 10 electrons
f - 14 electrons

Question 18

Order of sublevels -

Answer 18

1s2 , 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d10, 5p6

Question 19

When d - block elements form ions they lose

Answer 19

the 4s electrons first before 3d

Question 20

First ionisiation energies

Answer 20

The first ionisation energy is the amount of energy required to remove one mole electrons from gaseous atoms of that element

Question 21

First ionisation energy equation -

Answer 21

H(g) - H+ (g) + e -

Question 22

Second ionisation energy -

Answer 22

The second ionisation energy is the enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge

Question 23

Factors that affect ionisation energy -

Answer 23

• The attraction of the nucleus
  (The more protons in the nucleus the greater the attraction)
• The distance of the electrons from the nucleus
  (The bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus
• Shielding of the attraction of the nucleus
  (An electron in n outer shell is repelled by electrons in complete inner shells weakening the attraction of the nucleus)

Question 24

Successive ionisation energies

Answer 24

The patterns in successive ionisation energies for an element give us important information about the electronic structure for that element

Question 25

Periodicity is

Answer 25

A repeating pattern across a period is called periodicity

Question 26

Why do first ionisation energies decrease down a group -

Answer 26

As one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller

Question 27

Why is there a general increase in first ionisation energy across a period -

Answer 27

As one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective attraction of the nucleus greater

Question 28

Why has Na a much lower first ionisation energy than neon -

Answer 28

This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. So Na's outer electron is easier to remove and has a lower first ionisation energy

Question 29

Why is there a small drop from Mg to Al -

Answer 29

Al is starting to fill a 3p sub shell whereas Mg has its outer electrons in the 3s sub shell. The electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons