Atomic structure & periodic table Flashcards
* means something you don't have to memorise , just understand
mass of electron
what is an isotope-
1/1840
atoms with same no. of protons, different no. of neutrons.
what is ‘atomic’ number
what is ‘mass number’
-atomic number, Z = protons in the nucleus.
- mass number A= total no. of protons + neutrons in atom.
what is carbon 12
Carbon with 6 protons, 6 neutrons- considered to have mass of exactly 12
The most abundant isotope of carbon
what is the significance of carbon 12
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.
define relative isotopic mass
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)
define relative atomic mass
average mass (weighted mean mass) of one atom compared to one twelfth of the mass of one atom of carbon-12
key things to remember about relative isotopic mass
always a whole no.
no units
there is 1 relative isotopic mass for each isotope af an element
Compare chemical and physical properties of different isotopes of one element
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.
- difference between physical and chemical properties
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
equation for relative atomic mass
(relative isotopic mass x abundance%) + (same equation for isotope 2)
ALL divided by 100
*what is relative molecular mass
the average mass of a molecule
compared to one twelfth of the mass of one atom of carbon-12
what is the purpose of relative formula mass-
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
unit for:
relative molecular mass
relative atomic mass
Mr
Ar
purpose of mass spec
work out abundance and mass of isotopes of an element
- how does time of flight mass spec work- dont need to know
-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.’
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
-the energy in a moving object
-ions with same charge eg +1 /+3 will have same Kinetic energy
how does the detector determine mass and abundance
-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
why is the inside of a tof mass spec a vaccum
prevent ions collliding w/ air particles
in mass spectrum graph no. of peaks means-
no. of isotopes
y axis in mass spectrum graph
relative abundance %
x axis in mass spectrum graph
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
How to work out RAM from a mass spectrum graph
=∑ (isotopic mass x % abundance)
/100
OR
if given relative abundance instead of % abundance
= ∑ (isotopic mass x relative abundance)
total relative abundance
what is the isotopic mass of ²⁴Mg2⁺
the m/z mass to charge ratio is 24/2 so mass is 12
what is relative isotopic mass
mass of an isotope
how would you predict mass spectra for O2 . see 9. in chem notes
if a molecule eg ch4 is put through a mass spectrometer, why would you get a series of peaks
If a molecule is put through a mass spectrometer it
will often break up and give a series of peaks caused
by the fragments.
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
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)
in a mass spectra for a molecule eg
C4H10, what is the peak with the largest m/z called
parent ion/ molecular ion peak/ M+
what is the m+1 peak in mass spectrometry of a molecule
what influences the height of the m+1 peak
[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
a compound with 1 chlorine atom will have —– molecular ion peaks
explain why
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
a diatomic chlorine molecule/ a compound containing 2 chlorine atoms will have ——- molecular ion peaks
explain why
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
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
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
how can the relative abundance of the two isotopes be found.
compare the intensity of the signal/ the number of particles of each isotope detected in a mass spectrometer
what are the isotopes of oxygen
of chlorine
of bromineb
16, 17, 18
35, 37
79,81
