3.1.1 Atomic Structure Flashcards
Mass number definition
Total number of protons and neutrons in an atom. Known as A
Proton/atomic number definition
Number of protons in an atom. Known as Z.
Mass of a proton, neutron and electron
Proton: 1
Neutron: 1
Electron: 1/1840
Charge of a proton, neutron and electron
Proton: +1
Neutron: 0
Electron: -1
5 steps of TOF
- Ionisation
- Acceleration
- Ion drift
- Ion detection
- Data analysis
What information does TOF give
Relative isotopic mass
Relative isotopic abundance
Two methods of ionisation for TOF
Electron impact
Electrospray ionisation
Electrospray ionisation + equation
- Sample is dissolved in volatile solvent
- Injected through hollow needle connected to positive terminal of high voltage supply
- Each molecule gains a proton
M(g) + H+ –> MH+(g)
Electron impact + equation
- Sample is vaporised
- Electron fired at sample
- Electrons collide with sample and knock off an electron, forming positive ions
- Can cause fragmentation with large molecules
M+(g) e- –> M+(g) + 2e-
Why is it necessary to ionise samples in TOF
- Ions will interact with and be accelerated by an electric field
- Ions will create a current when they hit the detector
Detection stage of TOF
- Ions are accelerated towards a negatively charged metal plate
- Speed at which they reach the plate depends on their mass
- Positive ion picks up an electron from the detector, inducing a current
- The greater the abundance or charge the greater the current
First Ionisation energy
The amount of energy needed to remove one mole of electrons from one mole of gaseous atoms, forming a mole of gaseous 1+ ions
Ionisation energy trends
- Along the period ionisation energy increases as atomic radius decreases, meaning the electrons are more attracted to the nucleus and less easily lost
- Down the group ionisation energy decreases as shielding and atomic radius increases, so electrons are less attracted to the nucleus and more easily lost
Explain the pattern in the first ionisation energies of the elements from lithium to
neon. (6)
General trend
1. Ionisation energy generally increases along the period
2. Due to smaller atomic radius
3. And similar shielding
Deviation Be to B
4. B lower than Be
5. 2p sub shell is of higher energy than 2s sub shell
Deviation N to O
6. O lower than N
7. As it has paired electrons which repel each other
Relative atomic mass definition
Average mass of an atom of an element compared to 1/12 the mass of a carbon 12 atom
Relative molecular mass definition
Average mass of a molecule compared to 1/12 the mass of a carbon 12 atom.
Relative formula mass definition
Average mass of an ionic compound compared to 1/12 the mass of a carbon 12 atom.
What is Avogadro’s constant
The number of particles in a mole
6.022x10^23
How are moles calculated
Moles = Mass/Mr
Moles = concentration x volume
Ideal gas equation
PV = nRT
Ideal gas equation units
P- Pa
V - m^3
n - mol
R - 8.314
T - K
Empirical formula definition
The simplest whole number ratio of atoms of each element in a compound.
Molecular formula definition
The actual number of atoms of each element in a compound
Percentage atom economy equation
(Mr of desired product ÷Mr of reactants) x 100
