Structure of the atom and isotopes Flashcards
PEN?
Proton: 1, +1, nucleus
Electron: 1/1840, -1, energy levels surrounding the nucleus
Neutron: 1, 0, nucleus
How to calculate the maximum number of orbiting electrons that can be held by any single shell?
- Depends on the number of the shell (n)
- 2n^2
- e.g. electrons in shell 3 = 2(3^2) = 18
Atomic and mass number?
mass (A) - sum of protons and neutrons (1dp)
Atomic number (Z) - Number of Protons
Isotopes definition?
Atoms of the same elements with the number of protons but different number of neutrons (resulting in a different mass number)
Chemical & physical properties of isotopes?
- no. + arrangement of electrons: chemical - isotopes sames electron configuration so - same chemical properties
- physical tend to depend on mass e.g. densities/rate of diffusion
*Relative atomic mass definition (Ar)?
The weighted mean mass of an atom of an element, compared to 1/12th of the mass of an atom of carbon-12
- (is the avg of all the relative isotopic masses so - usually not whole no.)
- actual mass far too small to weigh normally so mass of 1 atom compared to mass of diff one - C-12
*Relative isotopic mass definition?
The mass of an atom of an isotope, compared with 1/12th of the mass of an atom of carbon-12
- e.g. 35 & 37 of Cl
Relative molecular mass (Mr) definition?
The average mass of a molecule or formula unit, compared to 1/12th of the mass of an atom of carbon-12
- molecular: simple molecules
- formula: compounds that are ionic/giant covalent
Working out Ar?
- Multiply each isotopic mass by its & add
- divide by 100
Ions definition?
Formed when an atom loses or gains electrons meaning it’s no longer neutral and will have an overall charge
What is Time of Flight Mass Spectrometry & the steps?
a form of spectrometry that: records the time it takes for ions of each isotope to reach a detector so - spectra produced showing each isotope present
- Ionisation
- Acceleration
- Ion Drift
- Detection
- Analysis
Ionisation?
- Ionisation: a sample of an element is vapourised + injected into the spectrometer - molecules bombarded with high energy electrons - electron is knocked off/removed from atoms- form +1 charged ions
Acceleration?
- Acceleration: + ions pass through an electric field which accelerated them into the instrument
Ion Drift?
- Ion Drift: ions then deflected by magnetic field into curved path - radius of their path dependent on charge + mass of ion
Detection?
- Detection: ion detector at the end of the tube responds to ions of a particular mass/charge ratio (m/z) and a mass spectrum is produced. (when the + ions hit the negatively charged detection plate - gain electron, producing flow of charge) - *the greater the abundance, the greater the current produced
Analysis?
- Analysis: these current values then used in combination w flight times to produce a spectra print-out w the relative abundance of each isotope displayed
Mass spectra?
- way to identify element from its isotopes
- spectrometers used to find out what samples are made up of by measuring the masses of their components
- x axis: m/z (mass/charge) : the mass of an isotope divided by charge - as most have +1 - m/z = isotopic mass
- y axis: % or not - If in % all isotopes abundances must add to give 100% - For an element height of each peak gives isotopic abundance
- can work out Ar -> then identify element
*isotopic mass must be whole no. (bcoz sum of p & n)
Predicting mass spectra?
- Write percentages as decimals
- Create a table showing the isotope combinations in a molecule of X
- Multiply the decimal abundances of each isotope to get: the relative abundance for each molecule - Any molecules which are the same (combo) add the abundances up
- Divide all the relative abundances by the smallest
- gives a whole number ratio to be used
Mass spectra of molecule?
- Peaks show fragments of the og molecule
- Last Peak: M + 1 peak/molecular iron peak - Same as RMM of molecule
- m/z: The mass of a fragment/charge aka the fragment mass
What are the three types of positive ions deflected by the magnetic field?
- Positively charged atoms
- Positively charged molecules
- Positively charged fragments of molecules
To find Ar of elements/compound containing two or more atoms covalently bonded?
- Figure out what the peaks are corresponding to e.g. Isotopic/molecular masses
- Work out ratio (using heights)
- Use ratio to work out the Ar how you would normally - Instead of ÷100, ÷ by sum of the ratio
To explain the relative heights of the molecular masses peaks?
- Draw a table for the atomic composition (Isotope combinations - mass & formula) of each molecule of X
- Using the isotope ratio, draw a table for the molecular composition (formula & ratio of molecules)…
- multiply the chances together - for the same chance: Add (use fractions)
How to work out Ar from graph?
- Multiply each relative Isotopic mass by abundance & add
- Divide by sum of abundances
How to find the relative molecular mass of a compound?
- Look at molecular ion peak aka peak with highest m/z value - Ignore small n + 1 peaks (occur due to presence of any atoms of carbon-13)
- m/z value = molecular mass
- From then use Mr to find compound
