Physical 1: Atomic Structure Flashcards
what are nucleons
protons and neutrons
relative mass of subatomic particles
proton = 1 neutron = 1 electron = 1 /1840
relative charge of subatomic particles
proton = +1 neutron = 0 electron = -1
atomic number
atomic number = number of protons
mass number
mass number = number of protons + number of neutrons
what is an isotope
same number of protons, different number of neutrons
different isotopes of the same element react in the same way chemically as they have the same electron configurations
what is mass spectrometer used for?
most useful instrument for accurate determination of relative atomic masses
relative atomic mass
Ar = (average mass of 1 atom) / (1/12 mass of 1 carbon 12)
relative molecular mass
Mr = (average mass of molecule) / (1/12 mass of 1 atom of carbon 12)
what are the six stages of time flight mass spectrometry?
- vacuum
- ionisation (2 methods)
- acceleration
- ion drift
- detection
- data analysis
Stage One of TOFMS - Vacuum
whole apparatus is kept under a high vacuum to prevent ions produced colliding with molecules in the air
stage two of TOFMS - Ionisation
- Electrospray Ionisation: sample is dissolved in a volatile solvent and forced through a fine hollow needle that is connected to the positive terminal of a high voltage supply. This produces tiny positively charged droplets get smaller until they may contain no more than a single positively charged ion
- Electron Impact: sample is vaporised and high energy electrons are fired at it from an electron gun, which is a hot wire filament with a current running through which emits a beam of high energy electrons —– this usually knocks off one electron from each particle forming a 1+ ion
X(g) + e- –> X+(g) + 2e-
stage three of TOFMS - acceleration
positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed
stage four of TOFMS - ion drift
the ions pass though a hole in the negatively charged plate, forming a beam and travel along a tube, called the flight tube, to the detector
stage five of TOFMS - detection
when ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. the flight times are recorded. the positive ions pick up an electron which causes a current to flow
stage six of TOFMS - data analysis
the signal from the detector is passed to a computer which generates a mass spectrum
what is an atomic orbital
an electron is considered to be a cloud of negative charge
the atomic orbital is the volume of space the electron fills up
what does the property ‘spin’ mean for electrons
two electrons in the same orbital must have opposite spin
the electrons are usually represented by arrows pointing up or down to show the different directions of spin
what are the three rules for allocating electrons to atomic orbitals
- atomic orbitals of lower energy must be filled first
- atomic orbitals of the same energy must fill singly before pairing due to electrons repelling
- no atomic orbital can hold more than two electrons
what is ionisation energy
required to remove a mole of electrons from a mole of atoms in the gaseous state and is measured in kJmol-1
has the abbreviation IE
ionisation energy trend across period 3
generally increase
ionisation energy change from magnesium to aluminium
-decreases-
despite the increase in nuclear charge
the outer electron in aluminium is in a 3p orbital which is slightly higher energy than the 3s orbital. It therefore needs less energy to remove it
ionisation energy change from phosphorus to sulfur
-decreases-
in phosphorus - each of the three 3p orbitals must contain one electron
in sulfur - one of the 3p orbitals must contain two electrons - the repulsion between these paired electrons makes it easier to remove one of them , despite the increase in nuclear charge
trends in ionisation energies down a group
general decrease because the outer electron is in a main level that gets further from the nucleus in each case
going down the group, the nuclear charge increases, however the positive charge ‘felt’ by an electron in the outer shell is less than full nuclear charge due to inner electrons shielding nuclear charge
