atomic structure

Question 1

what is the mass number

Answer 1

the protons and neutrons

Question 1

what is the atomic number

Answer 1

the number of protons in the nucleus

Question 2

what is an isotope

Answer 2

isotopes are atoms with the same number of protons and different number of neutrons

Question 3

what is the difference between isotopes and there atoms

Answer 3

they have similar chemical properties due to the fact they have the same electron arrangements
but slightly different physical properties due to their varying masses

Question 4

what does the mass spectrometer do

Answer 4

can be used to identify all the isotopes present in a sample of an element and therefore identify elements

Question 5

why does a mass spectrometer need to be a vacuum

Answer 5

if it was not a
vacuum air particles would ionise and register on the detector

Question 6

what is the first step in a mass spectrometer and what are the two ways of doing it?

Answer 6

ionisation where the atoms are turned into positive ions. there are two ways of doing this: electron impact and electron spray ionisation

Question 7

how does electron impact work

Answer 7

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

Question 8

how does electron spray ionisation work

Answer 8

the sample is dissolved in a volatile polar solvent.
it is then injected through a small needle giving a fine mist or aerosol
the tip of the needle has a high voltage and at the tip of the needle the sample gains protons H+
finally the solvent evaporates away and the positive ions move towards the negative plates

Question 9

what happens in stage two of a mass spectrometer

Answer 9

in stage two the ions accelerate by the electric field to a constant kinetic energy which can be worked out my
KE=1/2mv^2

Question 10

what changes the velocity of different particles

Answer 10

since all the particles have the same kinetic energy this means that the only thing that can effect the velocity is the mass. this means the lighter masses have a higher velocity and the heavier mases have a slower velocity

Question 11

what is the third stage in a mass spectrometer

Answer 11

the third stage is the flight stage where the particles move thought the vacuum with the same kinetic energy but different speeds and so separate depending on there mass. the ions are distinguished by their different flight times.

time of flight= length of flight tube x velocity of particle

Question 12

what is the fourth and final stage of a mass spectrometer

Answer 12

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

Question 13

what is the relative atomic mass

Answer 13

weighted average of all the isotopes of an element

the average mass of one atom of that elemt/ 1/12 of carbon 12

(isotope mass x relative abundance or % abundance) / 100

Question 14

what has mass spectrometer been used for in space

Answer 14

to identify elements on other planets. elements on other planets can have a different composition of isotopes.

Question 15

when is electron impact used in mass spectrometer vs when is electron spray ionisation

Answer 15

electron impact is used for substances with a lower formular mass as if it is larger it can caused it to fragment and electron spray is used for higher formular masses as it is gentler and wont cause fragmentation.

Question 16

how do you measure the Mr of a molecule when it has gone through electron impact in mass spectrometer

Answer 16

when molecules get hit with electron impact ionisation it will often cause the molecule to fragment and so give a series of peaks on the mass spectrum caused by the fragments. the highest peak however will be caused by the full molecule as it will have not fragmented and so you can figure out the Mr from that. this peak is called the molecular ion.

Question 17

how do you measure the Mr of a molecule when it has gone through electron spray ionisation

Answer 17

if a molecule is put through electron spray ionisation then it will not fragment. so their will be one speak equal to the MR of the ion. if you want the MR of the molecule it will be necessary to subtract one as it gained one extra proton at the start.

Question 18

how is the a level atom arranged

Answer 18

electrons are arranged in energy levels number 1 at the nucleus and 2,3,4.. outwards.
these energy levels are split into sub energy levels named s, p, d, f
these sub energy levels are split into orbitals which each hold up to two electrons off opposite spin

Question 19

what can the different sub energy levels hold

Answer 19

s- holds up to two electrons
p-holds up too 6 electrons
d- holds up to 10 electrons
f- holds up to 14 electrons

Question 20

what is an orbital

Answer 20

an orbital represent the mathematical probability of finding an electron at any point within certain spatial distributions around the nucleus. 95% chance of finding an electron

Question 21

what is a s orbital shaped like

Answer 21

a circle

Question 22

what does a p orbital look like

Answer 22

a infinity sign

Question 23

what is the exception to the rules with orbitals

Answer 23

4s comes before 3d

Question 24

what is the shorthand method to write the structures of the substructures

Answer 24

instead of writing out the full structure you can write the previous noble gas plus whatever is added on

Question 25

what are the two exceptions to the typical electron configuration in the subshells

Answer 25

copper has 3d^5 4s^1 instead of filling up 4s first and having 3d^4 4s^2 this is because occupying orbitals singly has lower energy

and chromium is 3d^10 4s^1 instead of 3d^9 4s^2 as complete d subshells are more stable

Question 26

what happens when transition metals form ions

Answer 26

they lose electrons from 4s before 3d

Question 27

explain the property of spin

Answer 27

electrons either spin up or down and only opposite spin electrons can be in the same orbital
and when filling orbitals they’ll fil singly first before doubling up