3.1.1 Atomic structure

Question 1

What is the relative mass of an electron?

Answer 1

1/1840

Question 2

What is Z?

Answer 2

Atomic/proton number

Question 3

What is A?

Answer 3

Mass/proton and neutron number

Question 4

What is an isotope?

Answer 4

Same number of protons but different number of neutrons.

Question 5

What does a mass spectrometer do?

Answer 5

Accurately determines relative atomic masses (Ar)

Question 6

Definition of Ar.

Answer 6

Average mass of 1 atom / 1/12 the mas of 1 atom of 12C

Question 7

Definition of Mr.

Answer 7

Average mass of 1 molecule / 1/12 the mass of 1 atom of 12C

Question 8

What is the first step of TOF mass spectrometry? What are the two different ways to do this?

Answer 8

Ionisation. Electrospray or electron impact/bombardment.

Question 9

What are the steps for electrospray ionisation?

Answer 9

Dissolved in volatile solvent
Forced through fine, hollow needle connected to the + terminal of a high voltage supply
Produces + charged droplets that’ve gained a proton from the solvent
Solvent evaporates to leave + charged ions

Question 10

What are the steps for electron impact ionisation?

Answer 10

Sample vapourised
High energy e-s fired at it from an e- gun
Knocks off an e- from each particle forming a 1+ ion

Question 11

What is the equation for electron impact?

Answer 11

X(g) + e- -> X+(g) + 2e-

Question 12

What is the second step of TOF mass spectrometry? How do we do this?

Answer 12

Acceleration
+ ions attracted to - plate and accelerates towards it
Lighter and higher charged ions achieve higher speeds

Question 13

What is the third step of TOF mass spectrometry? How do we do this?

Answer 13

Ion drift
Ions pass through a hole in the - charged plate
Form a beam and travel along the flight tube towards detector

Question 14

What is the last step of TOF mass spectrometry? How do we do this?

Answer 14

Detection
When ions with the same charge get to detector, lighter ones first (have higher velocities)
Flight times are recorded
\+ ions pick up an e- from the detector
Current flows

Question 15

What do we do with the data collected from a TOF mass spectrometry?

Answer 15

Data analysis

Signal from detector is passed to a computer which generates a mass spectrum

Question 16

What does a mass spectra do?

Answer 16

Identifies different isotopes that make up an element
Different isotopes = different masses
Peak height = relative abundance
x axis = m/z (singly charged ion = mass number)

Question 17

What is the calculation for Ar using a mass spectra?

Answer 17

(% x m/z) + (% x m/z) / 100%

Question 18

What are all the subshells?

Answer 18

1s2. 2s2, 2p6, 3s2, 3p6, 3d10, 4s2, 4p6, 4d10, 4f14

Question 19

What is the except to the linear filling of shells?

Answer 19

4s fills before 3d

Question 20

Define ionisation energy.

Answer 20

Energy required to remove a mole of electrons from a mole of atoms in the gaseous state. KJmol^-1.

Question 21

What is the general equation for the first ionisation energy?

Answer 21

X -> X+(g) + e-

Question 22

What is the trend in the 1st IE across a period?

Answer 22

Increases. Nuclear charge increases, more difficult to remove an e-.

Question 23

What are the exceptions to the trend across period 3? Why?

Answer 23

Mg-Al dips, because outer e- in AL is in a 3p orbital with a slightly higher energy than the 3s orbital, therefore less energy is needed to remove it.

P-S dips, because in P each 3p orbital only has 1e-, in S one of the 3p has 2e-s, repulsion between this pair makes it easier to remove one of them.

Question 24

What do the exceptions to the trend across a period prove?

Answer 24

Confirms existence of s and p sublevels.

Question 25

What is the trend in 1st IE down a group?

Answer 25

Decreases. outer e- is further from the nucleus, nuclear charge increases, more shielding.