Atomic Structure (Redone) Flashcards
Democritus’s views on particles
Made up of atoms which cannot be divided further
Boyle’s views on particles
Particles fixed in solids and free in liquids and gases.
Dalton’s views on particles
Atoms are indivisible and indestructible. Elements made up of the same atoms and compounds made up of different atoms
JJ Thomson’s views on particles
Plum pudding model. Electrons are -vely charged particles which are found in a cloud of positive charge
Rutherford’s views on particles
Mass isnt evenly spread, concentrated in the positive nucleus with electrons orbiting it. Electrons kept apart by forces of repulsion. Nucleus made up of protons which he discovered in his scattering experiment.
Explain Rutherford’s scattering experiment
Shot alpha particles at a thin foil sheet of gold and expected them to go straight through. Some were deflected
What did Rutherford conclude from his experiment
Most of the mass of an atom was concentrated in the centre in the nucleus
Nucleus was +ve to repel the alpha particles
Electrons must orbit the nucleus
Chadwick’s views on particles
Discovered neutrons which have same mass as protons but no charge
Bohr’s views on particles
Electrons orbit the nucleus in energy levels that have a fixed energy value
Why aren’t protons in the nucleus repelled?
Because there’s a strong nuclear force that acts over the nucleus and hold it together into a high density.
Define atomic number
The number of protons
Define mass number
The total number of protons and neutrons
Define an isotope
An atom of an element which has the same number of protons but a different number of neutrons. Same atomic number but different mass number
Why do isotopes have the same chemical properties?
Because they have the same electron configuration
Why do isotopes have different physical properties?
Because they have a different number of neutrons so they have a different mass
Define relative isotopic mass
The mass of a single isotope relative to the mass of 1/12 the mass of an atom of carbon-12.
Define isotopic abundance
The percentage of each isotope that occurs naturally on earth
Define relative atomic mass
The average mass of an atom of an element relative to 1/12th the mass of an atom of carbon-12.
Why is carbon-12 used as a standard?
Because its mass is exactly 12 and it’s practical because it’s a solid
What is mass spectrometry?
An instrumental method of analysis
What is mass spec used for?
To find Ar and Mr of elements and compounds. Find abundance and mass.
What are the stages of ToF mass spec?
Ionisation, Acceleration, Ion drift, Detection
Explain electron impact ionisation
Sample is vaporised
High energy electrons fired at it from an electron gun
Electron knocked off to form +ve ion
What is an electron gun
Hot wire filament with a current running through it that emits electrons
When is electron impact ionisation used?
For low formula mass compounds
Explain electrospray ionisation
Sample dissolved in volatile solvent (water/methanol)
Injected through fine hypodermic needle into a mist
Tip attached to +ve terminal of high voltage power supply
Ionised by gaining proton from solvent
Solvent dissolves to just leave sample
Write an equation for electron impact
X + e- —–> X+ + 2e-
Write an equation for electrospray ionisation
X + H+ —–> XH+
For which method does fragmentation occur?
Electron impact
Explain acceleration
Positive ions are accelerated using an electric field
Why are positive ions accelerated?
So that they all have the same kinetic energy so that some dont move faster bc they have more energy. Velocity based on mass
What is the relationship between the mass and the velocity of the particles?
Lighter particles travel faster
Why is there a vacuum in the mass spec?
So that the sample ions don’t hit the air molecules which will affect their flight path
Explain the flight tube
The time taken for positive ions to travel a set distance starting with a constant kinetic energy in an electric field is measured
Explain detection
+ve ions hit -ve plate. Discharged by gaining an electron. Movement of electrons causes a current that can be measured.
What does the number of peaks in a mass spec tell us?
Number of isotopes
What is the molecular ion?
The organic molecule with an electron knocked off to form a positive ion
Which peak is the molecular ion peak?
The last major peak at the highest m/z value
What is the base peak?
Peak with the greatest abundance
How does the distance between energy levels change as you go outwards
Shells get closer
What are shells made up of?
Sub shells
What are the different sub shells called?
s,p,d,f
What are sub shells?
Orbitals or a combination of orbitals
What are orbitals?
3D space which can hold up to two electrons
Why do electrons in an orbital spin in opposite directions?
To minimise repulsions
What’s the order of filling sub shells?
!s, 2s, 2p, 3s, 3p, 4s, 3d, 4p
Why does the 4s sub shell fill before the 3d?
because the n=3 and n=4 energy levels overlap so the 4s sub shell is lower than 3d
What is the ground state of an atom?
When electrons are in their lowest possible energy levels?
What ions do metals form and how?
Positive by losing an electron
What ions do nonmetals form and how?
Negative by gaining an electron
What ions can hydrogen form?
Hydrogen ion H+ or Hydride ion H-
What does isoelectronic mean?
Particles with the same electronic configuration
What is ionisation?
The process of removing electrons from ions and atoms
Define first ionisation energy
The enthalpy change when one mole of electrons is removed from one mole of gaseous atoms, forming one mole of gaseous singly charged cations
Define second ionisation energy
The enthalpy change when one mole of electrons is removed from one mole of singly-charged gaseous cations, forming one mole of doubly-charged gaseous cations
Write an equation for the first ionisation energy
X(g) —> X+ + e-
Write an equation for the second ionisation energy
X+ —-> X2+ + e-
Is ionisation exo or endo?
Endothermic bc energy is required to remove an electron from the attractive forces of the nucleus
How can we improve the existence of energy levels?
Successive ionisation energies of an atom show large jumps between shells bc more energy is required bc of increased effective nuclear charge (increase proton:electron ratio)
Why does ionisation energy decrease as you go down a group?
Atomic radius increases so outer electrons are further away from the attractive forces of the nucleus
More shells = more shielding
So less energy required to remove an outer electron
Why does first ionisation energy increase across a period?
Nuclear charge increases (more protons)
Atomic radius decreases (no extra energy levels)
No extra shielding
So more energy required to remove the outer electron
Why do Group 3 elements show lower than expected ionisation energy?
Division of subshell. 3p1 electron is further from the nucleus and has more shielding so less energy needed to remove it
Why do Group 6 elements show lower than expected ionisation energy?
Because they have 4 electrons in the p orbital so there’s one pair of electrons so there’s repulsion between them so less energy is required
Why do Group 1 atoms have the lowest ionisation energies in any period?
Biggest atomic radius (bc lower no of protons) and lowest nuclear charge
Why do Group 0 atoms have the highest ionisation energies in any period?
Because they have the smallest atomic radius and the highest nuclear charge
How are the patterns in second ionisation energy different to the first?
Shifted one to the left
