3.1.1 Atomic Structure

Question 1

mass number

Answer 1

total amount of protons + neutrons

Question 2

relative atomic mass

Answer 2

average mass of all isotopes in an element compared to 1/12th of Carbon - 12

Question 3

what does Mass Spectrometry determine?

Answer 3

-mass of atom / molecule
-isotopic abundance
-relative mass
-structure of complex molecules

Question 4

what are the 4 stages of mass spectrometry?

Answer 4

1) ionisation
2) acceleration
3) flight tube
4) detection

Question 5

what are the 2 methods of ionisation?

Answer 5

-Electron Impact
-Electrospray

Question 6

explain Electron Impact

Answer 6

-sample vapourised and injected at low pressure

-high energy electrons fired at sample by an electron gun

-1 and sometimes 2 outer electrons knocked off to form +1 or in some cases +2 charge

-X -> X+ + e-

Question 7

explain Electrospray

Answer 7

-sample is dissolved in volatile solvent (which is volatile so you can remove it later)

-injected at high pressure through fine needle attached to positive terminal to form a mist in chamber

-sample ionised by picking up H+ from solvent

-solvent evaporates while XH+ ions don’t

(C7H15N + H+ —> C7H16N+)

Question 8

explain Acceloration

Answer 8

-positive ions are accelerated using a negative plate
-regardless of mass all particles have same kinetic energy

Question 9

explain Flight Tube

Answer 9

-given that all particles have the same kinetic energy
-they will all travel at different speeds accord to their matter

Question 10

explain Detection

Answer 10

-positive ions hit negatively charged plate
-positive ions are discharged by gaining an electron
-current generated is measured

bigger abundance = bigger current = bigger signal

Question 11

how to calculate spectra of molecules for diatomic elements?

Answer 11

-add masses of the same, and different
-create a punnet square of them, labelling them with fractions based of their abundance
-assign the masses with fractions
-plot graph where x axis = mass number & y axis = ratio number

Question 12

equation for kinetic energy

Answer 12

2KEt^2 = md^2

Question 13

units for KE

Answer 13

J

Question 14

units for distance

Answer 14

m

Question 15

unit for time

Answer 15

s

Question 16

unit for mass in tof calculations

Answer 16

kg
-> only for tof mass calculations!!!
-> this IS NOT mass number (Ar) this the LITERAL mass
(use equation mass number = avogadros constant x mass)

Question 17

equation for mass

Answer 17

mass (g) = mass number / avogadros constant

the mass = the element in literal terms

Question 18

what type of molecule is electrospray usually used for

Answer 18

larger molecules so fragmentation does not occur

Question 19

why is mass spectrometry in a vacuum?

Answer 19

to prevent ions produced colliding with molecules in air

Question 20

what type of ions travel faster in TOF mass spectrometry

Answer 20

-all ions have constant kinetic energy
-lighter ions travel fastest since their velocity is dependent on their mass

Question 21

what does mass number always have to be

Answer 21

a whole number

Question 22

what do electrons occupy

Answer 22

orbitals

Question 23

what is an orbital?

Answer 23

a small pocket of space that can hold up to 2 electrons

Question 24

In 1s^2 what do each stand for?

Answer 24

1 = shell number / energy level
s = sub-orbital / sub-level
^2 = number of electrons in sub-orbital / sub-level

Question 25

ionisation energy

Answer 25

the energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions

Question 26

is ionisation an endothermic or an exothermic reaction?

Answer 26

endothermic -> takes in energy

Question 27

chromium electron configuration

Answer 27

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

Question 28

copper electron configuration

Answer 28

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

Question 29

what factors affect ionisation?

Answer 29

-**Atomic Radius** -**Shielding** -**Nuclear Charge**

Question 30

how does **Atomic Radius** affect ionisation?

Answer 30

-the greater the atomic radius the weaker the force of attraction between positive nucleus + outer electron being removed -ionisation energy **decreases**

Question 31

how does **Shielding** affect ionisation?

Answer 31

-more shielding leads to a weaker force of attraction between nucleus & electron -ionisation energy **decreases**

Question 32

how does **Nuclear Charge** affect ionisation?

Answer 32

-more protons, nucleus is more positive, force of attraction between nucleus + electron increases (atom smaller & more compact) -ionisation energy **increases**

Question 33

what happens to ionisation energy down a group?

Answer 33

-**decreases** -there is an increase in **atomic radius** -there is an increase in **shielding** -the force of attraction between nucleus + electron being removed is weakened -easier to remove electron

Question 34

what happens to ionisation energy across a period?

Answer 34

-**increases** -there is a decrease in **atomic radius** -as greater number of protons + electron cause atom to contract as the force of attraction is stronger -there is an increase in **nuclear charge** -**shielding** stays same

Question 35

exceptions for ionisation energy going across a period?

Answer 35

-group **2** -> **3** -group **5** -> **6**

Question 36

explain the exception for group **2** -> **3** ionisation energy going across a period?

Answer 36

-if electron being removed is from a higher energy level it means it’s easier to remove -the ionisation energy required is lower

Question 37

explain the exception for group **5** -> **6** ionisation energy going across a period?

Answer 37

-if electron is paired in sublevel -the electron experiences a force of repulsion -therefore requiring less energy to remove

Question 38

what makes an electron easier to remove

Answer 38

-if it’s higher in energy -if it’s experiencing a force of repulsion