Atomic structure & periodic table

Question 1

mass of electron
what is an isotope-

Answer 1

1/1840
atoms with same no. of protons, different no. of neutrons.

Question 2

what is ‘atomic’ number
what is ‘mass number’

Answer 2

-atomic number, Z = protons in the nucleus.
- mass number A= total no. of protons + neutrons in atom.

Question 3

what is carbon 12

Answer 3

Carbon with 6 protons, 6 neutrons- considered to have mass of exactly 12
The most abundant isotope of carbon

Question 4

what is the significance of carbon 12

Answer 4

masses in chemistry are relative/compared to mass of carbon 12, bcse the real mass of atoms in g or kg is too small to measure.

Question 5

define relative isotopic mass

Answer 5

mass of 1 atom of an isotope compared to 1/12 of the mass of 1 atom of carbon-12
(anything with 1/12 of mass of c12 is considered to have mass of 1)

Question 6

define relative atomic mass

Answer 6

average mass (weighted mean mass) of one atom compared to one twelfth of the mass of one atom of carbon-12

Question 7

key things to remember about relative isotopic mass

Answer 7

always a whole no.
no units
there is 1 relative isotopic mass for each isotope af an element

Question 8

Compare chemical and physical properties of different isotopes of one element

Answer 8

similar chemical properties -react in the same way bcse they have same electron configuration
MAY slightly vary in physical properties bcse they have different masses.

Question 9

• difference between physical and chemical properties

Answer 9

physical- physical characteristics of substance that can be observed/measured w/out changing identity of substance
chemical-ability of substance to undergo specific chemical change

Question 10

equation for relative atomic mass

Answer 10

(relative isotopic mass x abundance%) + (same equation for isotope 2)
ALL divided by 100

Question 11

*what is relative molecular mass

Answer 11

the average mass of a molecule
compared to one twelfth of the mass of one atom of carbon-12

Question 12

what is the purpose of relative formula mass-

Answer 12

used for compounds with giant structures like ionic compounds. EG large crystals will have more atoms than small crystals so we use the empirical formula- simplest whole number ratio of atoms of each element in compound and then work it out like we would with Mr

Question 13

unit for:
relative molecular mass
relative atomic mass

Answer 13

Mr
Ar

Question 14

purpose of mass spec

Answer 14

work out abundance and mass of isotopes of an element

Question 15

• how does time of flight mass spec work- dont need to know

Answer 15

-Sample of element/compound injected into a vaccum
-IONISATION- electrons fired at sample, all atoms ionised into +ve ions. (electron impact ionisation)
-ELECTRIC FIELD used to ACCELERATE +ve ions. (negatively charged plate attracts +ve ions, they speed to reach -ve side of field)
-IONS DRIFT- ions stop accelerating. they drift with no electric field at same speed they were travelling in the field
DETECTOR- lighter ions hit before heavier ions. ions gain electrons when hitting detector (to fill outer shell)- creating electric current that’s detected.’

Question 16

when the ions accelerate, the kinetic energy of the ions increases.
what is kinetic energy
will ions of the same charge eg +3 have same/different kinetic energy

Answer 16

-the energy in a moving object
-ions with same charge eg +1 /+3 will have same Kinetic energy

Question 17

how does the detector determine mass and abundance

Answer 17

-mass determined by time taken to hit detector
-ions drift down chamber at different velocities,reach detector earlier/later, lighter move faster
-abundance determined by size of current produced when each isotope hits detector
-more abundant isotope creates greater current

Question 18

why is the inside of a tof mass spec a vaccum

Answer 18

prevent ions collliding w/ air particles

Question 19

in mass spectrum graph no. of peaks means-

Answer 19

no. of isotopes

Question 20

y axis in mass spectrum graph

Answer 20

relative abundance %

Question 21

x axis in mass spectrum graph

Answer 21

m/z ratio
ratio of the mass of each ion to its charge

almost all ions have a +1 charge (1 electron knocked off in the mass spectrometer) so m/z is usually just the relative mass of the ion

Question 22

How to work out RAM from a mass spectrum graph

Answer 22

=∑ (isotopic mass x % abundance)
/100

OR
if given relative abundance instead of % abundance

= ∑ (isotopic mass x relative abundance)
total relative abundance

Question 23

what is the isotopic mass of ²⁴Mg2⁺

Answer 23

the m/z mass to charge ratio is 24/2 so mass is 12

Question 24

what is relative isotopic mass

Answer 24

mass of an isotope

Question 25

how would you predict mass spectra for O2 . see 9. in chem notes

Question 26

if a molecule eg ch4 is put through a mass spectrometer, why would you get a series of peaks

Answer 26

If a molecule is put through a mass spectrometer it
will often break up and give a series of peaks caused
by the fragments.

Question 27

what is important about the peak with the largest m/z (mass to charge ratio) / the last peak in a mass spec graph of a molecule

Answer 27

the peak with the largest m/z/last peak, will be due to the original complete molecule.
the m/z will be the Mr of the complete molecule (as long as its charge is +1)

Question 28

in a mass spectra for a molecule eg
C4H10, what is the peak with the largest m/z called

Answer 28

parent ion/ molecular ion peak/ M+

Question 29

what is the m+1 peak in mass spectrometry of a molecule
what influences the height of the m+1 peak

Answer 29

[M+1] peak is a smaller peak which is due to the natural abundance of the isotope carbon-13
-depends on how many carbon atoms are in that molecule; more carbon atoms= higher [M+1] peak

Question 30

a compound with 1 chlorine atom will have —– molecular ion peaks
explain why

Answer 30

2 peaks because there are two isotopes of chlorine.
some molecules may contain Cl35 while others will have Cl37. This changes the m/z or the molecular ions

Question 31

a diatomic chlorine molecule/ a compound containing 2 chlorine atoms will have ——- molecular ion peaks
explain why

Answer 31

3 molecular ion peaks because there are three different combinations of Chlorine atoms the molecule/compound can contain.
Cl35 and Cl35
Cl35 and Cl37
Cl37 andCl37

Question 32

in a mass spectrum of a chlorine molecule- Cl₂ what would the M+, M+2, M+4 peaks be caused by.

-which peak would be doubled in height

Answer 32

M+ would be due to Cl 35 and Cl 35
M+2 due to Cl 35 and Cl 37
M+4 due to Cl 37 and Cl 37

the M+2 peak- Cl 35 and Cl 37 - as there is a double chance of this being the combination

Question 33

how can the relative abundance of the two isotopes be found.

Answer 33

compare the intensity of the signal/ the number of particles of each isotope detected in a mass spectrometer

Question 34

what are the isotopes of oxygen
of chlorine
of bromineb

Answer 34

16, 17, 18
35, 37
79,81