Atomic structure Flashcards
mass number:
protons and neutrons
atomic number:
protons
isotopes:
atoms of the same element with the same number of protons but diff number of neutrons.
1803 John Dalton:
atoms are spheres that could not be divided into any smaller parts
1897 JJ Thompsomn:
discovered electrons
atoms was a sphere of positive charge with negative electrons embedded in it
1909 Ernest Rutherford:
discovered the nucleus
nucleus was very small and positively charged
concluded that atoms was mostly empty space
1913 Niels Bohr:
discovered problem with Rutherford experiment
electrons orbit the nucleus at specific distance
Describe the Experimental proof of Niels Bohr:
when EM radiation is absorbed the electrons move between shells
they emit this radiation when electrons move down to lower energy levels
define relative isotopic mass:
the mass of an atom of an isotope compared
with 1/12 of the mass of an atom of carbon-12
define relative atomic mass:
the weighted mean / average mass of an atom of an
element compared with 1/12 of the mass of an atom of carbon-12
define relative molecular mass:
the weighted mean/ average mass of a molecule
compared with 1/12 of the mass of an atom of carbon-12
define relative formula mass:
the weighted mean mass of a formula unit
compared with 1/12 of the mass of an atom of carbon-12
what are the four stages of mass spectrometer?
ionisation
acceleration
ion drift/ flight tube
detection
describe the process of ionisation: electron impact:
-vaporised sample is injected at low pressure
-an electron gun fires high energy electrons at the sample
-knocks out an electron forming a +1 ion
describe the process of ionisation:electron spray:
- sample is dissolved in a volatile polar solvent
-injected through a fine needle at high voltage
-at the tip of the needle the sample molecule gains a proton
-solvent then evaporates away while the + ions are attracted towards a negatively charged plate.
describe the process of acceleration:
-positive ions are accelerated by an electric field
accelerated to have the same KE
-+1 ions have the same KE so their velocity depends on their mass
what does the velocity of a particle depend on?
its mass and so lightest particle move faster than the heaviest particle
describe the process of ion drift:
positive ions enter the flight tube
particles will move at diff velocity depending on their mass
velocity at which an ions moves will determine its time of flight ( time it takes for particles to move through the tube)
t=d/v and KE=1/2mv^2
t=d square root of m/2KE
describe the process of detection:
once passed through the mass spectrometer the +1 ions will hit a negatively charged detector plate
as they hit the detector plate they gain an electron
gaining of the electron discharges the ion and causes a current to be produced
This size of the current is proportional to the abundance of those ions hitting the plate and gaining an electron
The detector plate is connected to a computer, which produces the mass spectrum
define ionisation:
- minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in gaseous state
describe the effect on shielding:
- the more electron shells between the positive nucleus and the negative electron that is being removed, the less energy required.
-there is a weaker attraction
describe the effect on nuclear charge:
-the more protons in the nucleus, the greater the attraction between the nucleus and outer electron
- this means more energy required to remove the electron
describe the effect on atomic size:
the bigger the atom, the further away the outer electrons are from the nucleus
less attractive forces between nucleus and outer electron so easier to remove
electron configuration of cr
1s2 2s2 2p6 3s2 3p6 3d5 4s1
define successive ionisation
-the removal of more than 1 electron from the same atom
why does ionisation energy decrease as we go down a group?
-the atomic radius increases as we go down the group because the outer electron is further away from the nucleus. weaker attraction forces . less energy required to remove electron
-Shielding increases . More shells between the nucleus and the outer shell. attractive forces are weaker . less energy needed to remove the electron.
why does ionisation energy increase as we move across a period?
-increasing number of protons in the nucleus . increases the nuclear attraction
-shielding is similar and distance from the nucleus marginally decreases,
- more energy is required to remove an outer electron.
Explain why the first ionisation energy of Al is less than that of Mg?
the outer electron of Al is removed from the 3p subshell whereas the outer electron in Mg is removed from the 3s subshell
the 3p subshell in in higher energy level than the 3s subshell
-aluminiums outer electron is further away from the nucleus and so weak attraction.-
less energy needed to remove outer electron in Al
Explain why the first ionisation energy of sulfur is different from that of phosphorus?
sulphur: 1s2 2s2 2p6 3s2 3p4
phosphorus: 1s2 2s2 2p6 3s2 3p3
In the 3p orbital of sulphur, the electrons are paired
In the 3p orbital of phosphorus, it contains a lone electron
paired electron in sulphur causes an electron repulsion so less energy is needed to remove an electron from an orbital of 2 in than 1 like Phosphorous
