Important Bits Atomic Structure and Amount of Substance Flashcards
Why is it necessary to ionise atoms in the sample?
Turn into positive ions to be detected and accelerated.
What is adjusted so each isotopes can be detected in turn?
Magnetic field, different fields of different masses reaching the detector.
Why is actual yield not 100 percent?
- Incomplete reactions
- Practical losses (eg. pouring or filtering)
- Side reactions
- Reversible reactions
- Impurities in reactants
Convert degrees C to K
+273
Convert KPa to Pa
x1,000
Convert cm^3 to m^3
x10^-6
Convert dm^3 to m^3
x10^-3
Easiest moles equation?
Moles = mass/Mr
Moles equation using volume of gas using dm^3?
Moles = volume of gas in dm^3 / 24
Moles equation using volumes of gas in cm^3?
Moles = volume of gas in cm^3 / 24,000
Equation for concentration in moldm^-3?
Conc. in moldm^-3n = conc in gdm^-3 / Mr
Factors that affect ionisation energy.
Atomic radius, nuclear charge, shielding.
Explain how atomic radius affects ionisation energy.
The closer the e-s to the nucleus the stronger the attraction from the nucleus to the e-s.
Explain how nuclear charge affects ionisation energy.
The more protons in the nucleus the stronger the attraction from the nucleus to the e-s.
Explain how shielding affects ionisation energy.
The less shells of e-s shielding/repelling the e-s the stronger the attraction from the nucleus to the e-s.
Equation for electron impact.
X(g) -> X+(g) + e-
Equation for electrospray.
X(g) + H+ -> XH+(g)
Electron impact summary.
- Sample vaporised
- ‘Electron gun’ fires high energy e-s at sample
- Knocks e- off
- Becomes 1+ ion
What is electron impact used for?
Low Mr compounds and elements.
Electrospray summary.
- Sample dissolved in volatile solvent
- Injected through fine hypodermic needle to give aerosol at high pressure
- High voltage applied through needle
- Each particle gains a proton (H+) ion
- Solvent evaporates
- Leaves 1+ ions
What is electrospray used for?
High Mr compounds (eg. proteins).
Define rel. atomic mass.
One atom of an element / 1/12 mass of one atom of carbon-12
Calculate Ar.
Total mass of all atoms / total number of atoms
What is special about Cr e- arrangement?
4s1, 3d5
What is special about Cu e- arrangement?
4s1, 3d10
Define 1st ionisation energy
The energy required to remove 1 e- from each atom in a mole of gaseous atoms producing 1 mole of gaseous 1+ atoms.
Ionisation energy trend down a group.
Downward trend. Bigger atomic radius, more shielding so weaker attraction from nucleus to e- in outer shell.
Ionisation energy trend across a period.
Upward trend. Increased nuclear charge, smaller atomic radius, similar shielding so stronger attraction from nucleus to e- in outer shell.
Exceptions to ionisation energy trend across a period.
Group 2-3 dip. Electron in p orbital higher energy than s subshell, extra shielding from extra s orbital so easier to remove e-.
Group 5-6 dip. G6 loses e- from orbital with 2 e-s (p4), G5 loses e- from orbital with 1 e- (p5) so extra electron repulsion makes it easier to lose form p4 than p5.
Define empirical formula.
The simplest whole no. ratio of atoms of each element in a compound.
Define molecular formula.
The actual no. of atoms in each element in a compound.
Steps to calculate empirical formulae.
% / mass in periodic table, / lowest no. from step 1, if fraction x to get whole no.s.
Steps to calculate molecular formulae.
Find empirical mass (little no. x mass in periodic), Mr/empirical mass, scale up by result in step 2.
Steps to calculate water of crystallisation.
% / formula mass of compound, / by lowest no. from step 1, that number is .x .
Define relative molecular mass (Mr).
Mr = average mass of one molecule / 1/12 mass of one element of carbon-12
Avagadro’s constant?
6.022 x 10^-23`
Define molar mass.
Mass of 1 mole of a substance in g.
Steps to reacting mass calculations.
Find moles of one you know, use ratio in equation to get moles of unknown, mass = moles x Mr.
Steps to calculating volumes of gases in equations.
Moles of one you know, ratio to find one you don’t, vol. = moles x 24.
Equation for % yield?
% yield = actual yield / theoretical yield x 100
Define actual yield.
What you make in the lab.
Define theoretical yield.
What you should make using a calculation.
% atom economy equation?
% atom economy = total Mr of desired product / total Mr of all reactants x 100
For % atom econ. what should you include in calculations?
BIG NUMBERS!
Moles equation using conc. and vol.?
Moles = conc. x vol. in dm^3
Steps to titration calculations.
Find the moles of one you know (use vol. and conc.), find moles of unknown with equation, find conc. of unknown (conc. = moles/vol. in dm^3)
