Atomic structure

Question 1

define what an isotope is

Answer 1

atoms with the same number of protons but different number of neutrons

Question 2

what are the two types of ionisation?

Answer 2

1. electrospray
2. electron impact

Question 3

why does mass spectrometer need to be under a vacuum

Answer 3

this is so that air particles dont ionise and register on the detector

Question 4

describe electron impact ionisation

Answer 4

a vapourised sample is injected at low pressure and an electron gun fires high energy electrons at the sample this knocks off an electron forming a 1+ ion

Question 5

equation for electron impact

Answer 5

Ti (g) —— Ti + (g) + e-

Question 6

describe electrospray ionisation

Answer 6

the sample is dissolved in a volatile solvent and is then injected through a fine hypodermic needle giving a fine mist. the tip of the needle has high voltage at the tip of the needle the sample gains a proton from the solvent forming XH+

Question 7

what is electron impact typically used for ?

Answer 7

for elements and substances with a low formula mass ( fragmentation)
electron impact can cause larger organic molecules to fragment

Question 8

whats electrospray ionisation used for?

Answer 8

used for larger organic molecules . the “softer” conditions means fragmentation doesnt occur

Question 9

Acceleration - what happens?

Answer 9

• positive ions are accelerated by an electric field to a constant velocity.
  NOTE: given that all particles have the same kinetic energy the lightest particles will reach the detector first.

Question 10

Detection ( final step)

Answer 10

the ions reach the detector and generate a small current. the current is produced by electrons transferring from the detector to the positive ions

Question 11

which is lost first when forming an ion 3d or 4s?

Answer 11

4s

Question 12

define first ionisation energies

Answer 12

The first ionisation energy is the energy required to remove one mole of electrons from one mole of atoms of an element to form one mole of 1+ ions E.g. the first ionisation energy of gaseous calcium:
Ca (g) → Ca+ (g) + e-

Question 13

define second ionisation energies

after1st ionisation energy

Answer 13

Second ionisation energy is defined by the equation:

X+(g) X2+(g) + e-

It is the energy required to remove a second electron from each ion in 1 mole of gaseous 1+ ions to give gaseous 2+ ions.

Question 14

what are the factors that affect ionisation energies

Answer 14

1) nuclear charge ( the more protons in the nucleus the greater the attraction)
2) shielding ( an electron in an outer shell is repelled by electrons in complete inner shells )
3) atomic radius ( the bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus.

Question 15

why are successive ionisation energies always larger?

Answer 15

this is because when the first electron is removed it forms an positive ion. The ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger

Question 16

why does Helium have the largest ionisation energy?

Answer 16

its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. Helium has a bigger first ionisation energies than H as it has one more proton.

Question 17

why does ionisation energy decrease down a group?

Answer 17

this is because as you go down the group the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of nucleus becomes smaller

Question 18

why is there a general ionisation energy increase across a period?

Answer 18

as you go across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. however the number of protons increases making the attraction of the nucleus greater

Question 19

why does sodium (Na) have lower ionisation energy than neon?

Answer 19

this js because Na will have its outer electron in the 3s subshell further from the nucleus and is more shielded therefore meaning Na outer electron is easier to remove and has a lower ionisation energy

Question 20

why is there a small drop from Mg to Al?

Answer 20

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

Question 21

why is there a small drop from P to S

Answer 21

this is because in sulfur there are 4 electrons in the 3p subshell meaning that one of the 3p orbital will be fully filled this causes a slight repulsion between the two negatively charged electrons which makes the electron in sulfur easier to remove

Question 22

define the term orbital

Answer 22

a region around the nucleus which can hold up to two electrons