atomic structure 3.1.1 in papers 1 & 3 Flashcards
(26 cards)
list the different atomic models over the years.
- Dalton
atoms are indivisible, atoms of each element have different masses. - Thomson
atom is positively charged sphere embedded with negative electrons. - Rutherford
the mass of the atom is concentrated is a tiny positively charged center. - Bohr
electrons have fixed energy levels - Shrondinger
electrons are found in orbitals.
what are isotopes?
- atoms with the same number of protons, but different numbers of neutrons.
- they have similar chemical properties because they have the same shell structure.
- they may have slightly varying physical properties due to the different masses.
time of flight mass spectrometry
what is mass spectrometry?
A powerful instrumental method of analysis that can be used to:
- find the abundance and mass of each isotope in an element allowing us to determine its relative atomic mass.
- find the molecular atomic mass of substances made of molecules.
time of flight mass spectrometry
what are the 2 ways a sample can be ionised?
- electron impact ionisation (gun method)
- electrospray ionisation
time of flight mass spectrometry
what is electron imapct ionisation?
- the sample is vapourised and fired with high energy electrons from an electron gun which knocks of 1 electron from each particle.
- the ions formed are attracted towards a negative plate where they are accelerated.
time of flight mass spectrometry
what is electrospray ionisation?
- the sample is dissolved in a volatile solvent and injected through a fine needle to give a fine mist.
- the tip of the needle is attached to the positive terminal of high voltage power supply.
- the particles are ionised by gaining a proton (H+) from solvent as they leave the needle.
time of flight mass spectrometry
what is electron imapct ionisation used for?
- X (g) + e -> X+ (g) + 2e
- elements
- substances made of molecules with a low molecular mass.
- however molecules often fragment.
time of flight mass spectrometry
what is electron spray ionisation used for?
- X(g) + H+ -> XH+(g)
- substances made of molecules with a high molecular mass, including biological ones (proteins).
- molecules rarely fragment.
- resulting ions have a Mr one unit higher due to gain of protons.
- cant be used if particles arent capable o gaining a proton.
time of flight mass spectrometry
what happens in stage 2?
- acceleration
- positive ions are accelerated using an electron field so that they all have the same kentetic energy.
- KE = joules
- mass = KG
- given particles have the same kenetic energy, the velocity of each one depends on its mass, lighter ones are faster.
time of flight mass spectrometry
what happens in stage 3?
- flight tube
- the positive ions travel through a hole in the negatively charged plate into a tube.
- the time of flight depends on velocity which depends on mass.
- v=d divided by t
time of flight mass spectrometry
what happens in stage 4?
- detection
- the postive ions hit a negatively charged electric plate.
- the ions reach the detector and generate a small current, which is fed to a computer for analysis.
- the current is produced by electrons transferring from the detector to the positive ion.
- the size of the current is proportional to the abundance of the species.
- the size of the current gives a measure of the number of ions hitting the plate.
time of flight mass spectrometry
what happens in stage 5?
- data analysis
- a computer uses the data to produce a mass spectrum.
- shows mass of the ion.
time of flight mass spectrometry
how do you work out the Ar?
total mass of each isotope
—————————-.
total abundance
mass spectrometry
how do you work out the relative atomic mass?
R.A.M = (isotopic mass x relative abundance)
—————————-.
total relative abundance
mass spectrum
explain the mass spectrum graph.
- furthest to the right of the significant peaks = molecular ion peak.
- mass/charge = Mr of the molecule.
- other peaks are fragments you ignore.
TOF
calculate the mass of an ion of a particular isotope in Kg.
mass = Ar/L
TOF
calculate velocity of the ion in a particular isotope as it travels through the flight tube.
v = 2KE
-.—–
m
square root it
TOF
how do u calculate the legnth of the flight tube?
d = vt
(need to work out mass then velocity then distance).
electron configuration
what are the 2 types of energy levels?
- principle (main shell, assigned numbers, 1,2,3 etc)
- subsidary ( orbitals, assigned letters s,p,d,f etc)
electron configuration
name each sub level and the maximum number of electrons they hold.
s level - 2
p level (3 types) - 6
d level (5 types) - 10
f level (7 types) - 14
electron configuration
define orbitals.
- a 3D region of space where an electron is found.
- can hold 2 electrons but will have opposite spin to overcome the repulsion between them.
electron configuration
what is the shell order?
only need to know up to 4s
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d10 etc.
- lower energy orbitals are filled first.
electron configuration
what is the electron configuration for chronium and copper?
they are the exceptions
Cr- 1s2, 2s2, 2p6, 3s2, 3p6, 3d5, 4s1
Cu- 1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s1
ionisation energy
what is ionisation energy?
- the energy required to remove a mole of electrons from a mole of atoms in the gaseous state.
- used only for positive ions.
- first ionisation: H(g) -> H+(g) + e-
- second ionisation: : Ti+(g) -> Ti2+(g) + e-
