Physical 1: Atomic Structure

Question 1

what are nucleons

Answer 1

protons and neutrons

Question 2

relative mass of subatomic particles

Answer 2

proton = 1 
neutron = 1 
electron = 1 /1840

Question 3

relative charge of subatomic particles

Answer 3

proton = +1
neutron = 0 
electron = -1

Question 4

atomic number

Answer 4

atomic number = number of protons

Question 5

mass number

Answer 5

mass number = number of protons + number of neutrons

Question 6

what is an isotope

Answer 6

same number of protons, different number of neutrons

different isotopes of the same element react in the same way chemically as they have the same electron configurations

Question 7

what is mass spectrometer used for?

Answer 7

most useful instrument for accurate determination of relative atomic masses

Question 8

relative atomic mass

Answer 8

Ar = (average mass of 1 atom) / (1/12 mass of 1 carbon 12)

Question 9

relative molecular mass

Answer 9

Mr = (average mass of molecule) / (1/12 mass of 1 atom of carbon 12)

Question 10

what are the six stages of time flight mass spectrometry?

Answer 10

1. vacuum
2. ionisation (2 methods)
3. acceleration
4. ion drift
5. detection
6. data analysis

Question 11

Stage One of TOFMS - Vacuum

Answer 11

whole apparatus is kept under a high vacuum to prevent ions produced colliding with molecules in the air

Question 12

stage two of TOFMS - Ionisation

Answer 12

1. Electrospray Ionisation: sample is dissolved in a volatile solvent and forced through a fine hollow needle that is connected to the positive terminal of a high voltage supply. This produces tiny positively charged droplets get smaller until they may contain no more than a single positively charged ion
2. Electron Impact: sample is vaporised and high energy electrons are fired at it from an electron gun, which is a hot wire filament with a current running through which emits a beam of high energy electrons —– this usually knocks off one electron from each particle forming a 1+ ion
   X(g) + e- –> X+(g) + 2e-

Question 13

stage three of TOFMS - acceleration

Answer 13

positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed

Question 14

stage four of TOFMS - ion drift

Answer 14

the ions pass though a hole in the negatively charged plate, forming a beam and travel along a tube, called the flight tube, to the detector

Question 15

stage five of TOFMS - detection

Answer 15

when ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. the flight times are recorded. the positive ions pick up an electron which causes a current to flow

Question 16

stage six of TOFMS - data analysis

Answer 16

the signal from the detector is passed to a computer which generates a mass spectrum

Question 17

what is an atomic orbital

Answer 17

an electron is considered to be a cloud of negative charge

the atomic orbital is the volume of space the electron fills up

Question 18

what does the property ‘spin’ mean for electrons

Answer 18

two electrons in the same orbital must have opposite spin

the electrons are usually represented by arrows pointing up or down to show the different directions of spin

Question 19

what are the three rules for allocating electrons to atomic orbitals

Answer 19

1. atomic orbitals of lower energy must be filled first
2. atomic orbitals of the same energy must fill singly before pairing due to electrons repelling
3. no atomic orbital can hold more than two electrons

Question 20

what is ionisation energy

Answer 20

required to remove a mole of electrons from a mole of atoms in the gaseous state and is measured in kJmol-1
has the abbreviation IE

Question 21

ionisation energy trend across period 3

Answer 21

generally increase

Question 22

ionisation energy change from magnesium to aluminium

Answer 22

-decreases-
despite the increase in nuclear charge
the outer electron in aluminium is in a 3p orbital which is slightly higher energy than the 3s orbital. It therefore needs less energy to remove it

Question 23

ionisation energy change from phosphorus to sulfur

Answer 23

-decreases-
in phosphorus - each of the three 3p orbitals must contain one electron
in sulfur - one of the 3p orbitals must contain two electrons - the repulsion between these paired electrons makes it easier to remove one of them , despite the increase in nuclear charge

Question 24

trends in ionisation energies down a group

Answer 24

general decrease because the outer electron is in a main level that gets further from the nucleus in each case
going down the group, the nuclear charge increases, however the positive charge ‘felt’ by an electron in the outer shell is less than full nuclear charge due to inner electrons shielding nuclear charge