Atomic Structure Flashcards
What does an atom consist of? Charges and masses?
Electrons - negative charge, mass of 1/1840
Protons - positive charge, mass of 1
Neutrons - no charge, mass of 1
Nucleus with protons and neutrons in, electrons in shells
The evolution of the atom
Thomson - discovered the electron (plum pudding model - positively charged ball with electrons dotted in)
Rutherford - electrons orbit with most of the mass concentrated in the nucleus (alpha particle test)
Bohr - electrons move in orbits
What is an isotope?
Element with same proton number, different number of neutrons
Time of Flight Spectrometer Method
Sample injected with a hypodermic needle
Ionisation
Acceleration
Separation
Detector
TOF - Electron Impact Ionisation
Used for elements/substances with a low Mr
Shoot high energy electrons from an electron gun at the sample
It knocks of an electron - forming a 1+ ion
It is random so often breaks down into fragments that get detected on the spectrum
TOF Electron Impact Ionisation Equation
X(g) + e- —> X+ (g) + 2e-
Or
CH4 (g) + e- —> CH4+ (g) + 2e-
TOF - electrospray ionisation
Used for high Mr molecules/elements
Rarely gives fragments
Sample is dissolved in a volatile solvent
Injected with the hypodermic needle
Tip of needle has a voltage applied to it
Each molecule gains a H+ proton
TOF electrospray ionisation equation
M (g) + H+ —> MH+ (g)
TOF -acceleration of ions
1+ ions are accelerating using an electric field (negatively charged plate)
So all the ions have the same kinetic energy (Ek)
Formula - Ek = 1/2mv^2
TOF - separation of ions
Positive ions travel through a hole in the negative plate into the flight tube
TOF of each particle depends on its velocity (and hence its mass)
d = vt
TOF - detection
Detector is a negatively charged plate (ions gain e-)
This generates a current
The size of current is proportional to the abundance of isotopes
Relative atomic mass equation (using abundance)
(Mass x abundance) + (mass x abundance) / total abundance
TOF calculations
To find mass - Ar / L (Avogadro’s Constant) / 1000 to get it into kg
To find velocity - rearrange equation using the mass you just found
To find distance - use the velocity you just found x time (in metres)
Mass spectra
Chlorine ratio = Cl35 (75%) and Cl37 (25%)
Bromine ratio = Br79 (50%) and Br81 (50%)
Find the possible outcomes which reflect the ratios
The more abundant the isotope is, the higher the peak is
How to predict the appearance of mass spectra for diatomic molecules
Make the isotopes into a ratio
Change the ratio into fraction form
Calculate the possibilities of combinations by MULTIPLYING the fractions together
Add together any that have 2 possibilities
Simplify back into a ration (can be decimal or percentage)
What are the 4 sub shells and how many electrons can be held in each
S = 2
P = 6
D = 10
F = 14
How to remember the filling order for electron configuration
4S is filled before 3D
This is because 4S has lower energy
1
2s 2p
3s 3p 3d
4s 4p 4d 4f
Short structure + how electrons fill up in electron configuration
Electrons prefer to be on their own in the orbitals, however do pair up when no or orbitals left of the same energy
Short structure - use the noble gas before the element and then rest of structure
E.g 1s2 2s2 2p5 = [He] 2s2 2p5
Electron configuration - pesky transition metals
Chromium = 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Promoted 1 e- to 3d, both have half filled sub-levels
Copper = 4s1 3d10
One half filled and one full
What is it called when electrons have the same configuration?
Isoelectronic species
As you go down a group, why does the atomic radius increase?
More electron shells/shielding
Has a weaker attraction between the nucleus and the outer electrons
As you go across a period, why does the atomic radius decrease?
Electrons are in the same shell (same shielding)
Therefore, there is a stronger attraction between the nucleus and the outer electrons
More protons means bigger nuclear charge (pulling electrons closer)
Definition of first ionisation energy
Enthalpy change required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
Example of ionisation energy equations
1st Na (g) —> Na+ (g) + e-
2nd Na+ (g) —> Na2+ (g) + e-
What 3 factors affect the first ionisation energy
Distance from the nucleus (atomic radius)
The closer the electron being removed to the nucleus, the stronger the attraction between the nucleus and the outer electron
Nuclear charge
The more protons, the stronger the attraction is between the nucleus and the electron being removed
Shielding
The less inner shells of electron shielding, the stronger the attraction between the nucleus and the outer electron
Less shielding = higher ionisation energy
As you go down a group, what happens to the ionisation energy and why?
Ionisation energy decreases
Why =
More electron shielding meaning more full electron inner shells
Larger atomic radius - electron being removed is further from the nucleus
Means a weaker attraction between the nucleus and the electron being removed
As you go across a period, what happens to the ionisation energy and why?
The ionisation energy increases
Why =
Same shielding
Increase in nuclear charge
Smaller atomic radius so stronger attraction between the nucleus and electron being removed
Deviation in the ionisation energy across a period
Dip from group 2 to 3
Electron is removed from the 3p orbital
It is slightly further away from the nucleus ( + higher energy)
Dip from group 5 to 6
A pair of electrons in the 3p orbital which REPEL each other
