Physical Chemistry- Atomic Structure Flashcards
What is the charge and mass of:
Proton
Neutron
Electron
Charge
P- +1
N- 0
E- -1
Mass
P-1
N-1
E-1/1840
What decides the chemical properties of an element?
Electron configuration
Why do isotopes have the same chemical properties?
They have the same electron configuration
Why do isotopes have slightly different physical properties?
Physical properties depend on the mass of the atom. Isotopes have different mass numbers.
What is the relative atomic mass?
The average mass of an atom of an element relative to 1/12th the mass of one atom of carbon-12
What is relative isotopic mass?
Mass of an isotope relative to 1/12th the mass of one atom of carbon-12
How to calculate relative atomic mass?
(Isotopic mass x percentage abundance)/100
What does a mass spectrometer calculate?
Relative atomic mass of an element and relative abundance of its isotopes
What are the four stages of mass spectrometry?
1) Ionisation
2) Acceleration
3) Ion drift
4) Detection
What is electron impact ionisation?
1) Sample is vapourised
2) Electron gun fires a high energy electron at sample causing for an electron to be knocked off
3) A +1 ion is formed
What is electro spray ionisation?
1) Sample is dissolved in a volatile solvent
2) Sample is injected into mass spectrometer through a hypodermic needle to give a fine mist
3) Tip of the needle is attached to the positive terminal of a high voltage supply
4) A high voltage is applied causing for it to gain a proton
5) The solvent is removed, leaving a gas
NB- sample increases in mass by 1 (+H)
What happens during acceleration?
An electric field accelerates the positive ions.
It gives the same kinetic energy to the ions with the same charge.
Lighter ions experience a greater acceleration than heavier ions
What happens during ion drift?
Ions enter a region with no electric field
They drift through the region at same speed as they left the electric field
What happens during detection?
The positive ions hit the detector
They gain an electron= causes for current to be produced
Detector detects current produced and time taken for ion to pass through spectrometer= size of current is directly proportional to abundance of the ion
Why must the sample be ionised?
So that it can be detected and accelerated = electric field will only accelerate ions
Why must the spectrometer be kept under vacuum?
Prevents the ions colliding with air moleules
What are the different types of sub-shells?
s sub-shell = 1 orbital = 2 electrons
p sub-shell = 3 orbitals = 6 electrons
d sub-shell = 5 orbitals = 10 electrons
f sub-shell = 7 orbitals = 14 electrons
What is an orbital?
An orbital holds up to 2 electrons that have opposite spins
Define molecule
Two or more atoms covalently bonded together (Cl2, H2, H2O, CO2)
Define compound
Two or more different types of atoms ionically/covalently bonded together
Formulae of acids
Hydrochloric acid
Nitric acid
Sulfuric acid
Phosphoric acid
HCl
HNO3
H2SO4
H3PO4
Define an acid
A substance that donates H+ ions/protons
Define a base
A substance that accepts H+ ions/protons
Define an alkali
A base that releases OH- ions in an aqueous solution
Define ionisation energy
Ionisation energy is the amount of energy required to remove one mole of electrons from one mole of atom in the gaseous state
What factors affect ionisation energy?
1) Distance between e- to be removed and nucleus
2) Amount of shielding
3) Number of protons
Explain the trend of the first ionisation energy down a group
IE decreases
More shielding
More shells
Greater atomic radius
So force of attraction between nucleus and outer electron is weaker = less energy is required
Explain the trend of the first ionisation energy across a period
IE increases
Same shielding and number of shells
Number of protons in nucleus increase = more attraction between nucleus and outer electron = more energy is required
Example of a deviation in trend of IE across a period
Group 2: Be - B
Group 3: Mg - Al
E- being removed in B is in the 2p subshell = further away from nucleus = more shielding = weaker force of attraction between nucleus and outer e-
Why do successive IEs increase?
Each subsequent electron needs greater IE to be removed from a more positive ion = attraction between the nucleus and outer electron is stronger
