how has the atomic model developed over time
plum pudding model
electron shell model
relative mass/ charge of particles
- proton: +1, 1 mu
- neutron: 0, 1 mu
- electron: -1, 1/1840 mu
what consists an atom?
a nucleus containing protons and neutrons surrounded by electrons
what holds particles in an atom together?
- protons+neutrons are held together by the strong nuclear force
- electrons+protons are held together by electrostatic forces (weaker than strong nuclear forces)
what is the mass number of an atom (represented by A)?
no. of protons+no. of neutrons in atom ∴ has to be a whole number
what is the atomic number of an atom (represented by Z)?
no. of protons in an atom
how to calculate Ar
[(abundance of isotope 1 x mass) + (abundance of isotope 2 x mass)]/sum of abundances
isotopes definition in terms of…
- fundamental particles - atoms of the same element with the same no. of protons but diff no. of neutrons
- atomic/mass number - atoms of the same element the same atomic number but diff mass number
uses of mass spectrometry
- provides accurate info abt relative isotopic mass and relative abundance of isotopes
- identify elements
- determine relative molecular mass of molecules
- deduce info abt structure of molecules
characteristics of TOF mass spectrometry
- used to determine the mass of an element or compound
- speed ions travel at is dependent on their mass to charge ratio (m/z)
TOF mass spectrometry
- Ionisation - sample is vapourised+injected into mass spectrometer where a high voltage is passed over the chamber=sample is ionised as electrons are lost=1+ ions left
- Acceleration - Positive ions are attracted to negatively charged
plate which accelerates it. Lighter ions=higher speed - Ion drift - Ions pass through a hole in (-ve) plate, forming a beam and travel along flight tube.
- Detection - lighter ions will arrive at detector quicker than heavier ions with the same charge. Flight time recorded. Positive ions gain an electron from the detector=current to flow
- Data analysis - signal from detector is passed to a computer=generates a mass spectrum
What are the diff types of ionisation for TOF mass spectrometry?
- electrospray
- electron impact
what is electron impact?
- sample is vaporised
- high energy electrons are fired at it=loss of an electron from each particle=forms a 1+ ion
electron impact equation
X(g)+e- → X+ + 2e-
what is electrospray?
- sample is dissolved in a volatile solvent+injected through a fine hypodermic needle=fine mist
- particles gain a proton from the solvent
electrospray equation
X(g) + H+ → XH+(g)
first ionisation energy definition
the energy needed to remove 1 mole of gaseous electrons from 1 mole of gaseous atoms of an element to 1 mole of gaseous ions w a single positive charge
first ionisation energy equation
X(g) –>X+(g) + e-
second ionisation energy definition
the energy needed to remove 1 mole of gaseous electrons from 1 mole of gaseous single charged ions of an element to 1 mole of gaseous ions w a double positive charge
second ionisation energy equation
X+(g) –>X2+(g) + e-
successive ionisation energies
refer to 1st, 2nd, 3rd, etc IE for a particular element
factors influencing ionisation energies
- nuclear charge=more protons=more + charged nucleus=more strongly attracted electrons are to it=harder to lose
- electron shielding=more shells=↓attraction between nucleus +outer electron=easier to lose
- distance from outermost electron from nucleus=electron closer to nucleus=↑attracted=↑tightly held=harder to lose
1st IE trend down a group
- ↑ nuclear charge
- ↑ distance from outer electron from nucleus
- ↑ shielding
∴ ↓ IE down a group=easier to remove outer shell electrons
1st IE trend across a period
- ↑ nuclear charge
- electron being removed from same shell=same shielding
- across a period → (generally) greater attraction between electron being removed+nucleus=∴ ↑ energy required to remove it
- ∴ ↑IE
