Atomic Structure Flashcards
Timeline of model of the atom
- Democritus
- John Dalton
- J.J Thompson
- Rutherford
- Neils Bohr
- James Chadwick
Democritus
- Greek philosopher
- atomos = indivisible
- atoms could not be split
John Dalton
- came up with atomic theory
- all matter composed of atoms
- they are indivisible and indestructible building blocks
- represented atoms as hard spheres that couldn’t be split
- atoms of an element were identical
- different elements had atoms of different size and mass
J.J Thompson
- atoms were indivisible
- discovered atoms contained negatively charged particles (electrons)
- put forward plum pudding model
- atoms were spheres of positive charge with negative electrons randomly embedded throughout
- realised when discovering electrons that atoms could not be solid spheres and could be broken down into smaller subatomic particles
Rutherford
- gold foil experiment proves that plum pudding model was incorrect
- fired positively charges alpha particles through gold foil
- proved that atoms have their positive charge concentrated in a very tiny volume and that most of the atom was completely empty space
- if the plum pudding model correct, then most of the alpha particles fired at the gold foil would be deflected, but most passed straight through
Niels Bohr
- if electrons were a ‘cloud’ around the nucleus then it would spiral sown into the he nucleus causing it to collapse
- thus Bohr proposed a new theory:
- electrons can only exist in fixed orbits/shells
- each shell has a fixed energy
Niels Bohr revised model
- scientists discovered that not all electrons in the same shell had the same energy
- meant somehow the previous Bohr model wrong
- refined to add sub-shells/orbitals
- Bohr believed each shell can only hold a fixed number of electrons
- also, elements reactivity is due to its electrons, so when the shell is full, it is inert.
- modified Bohr model includes the idea of sub shells and orbitals and we still use this model to explain basic ideas about bonding
James Chadwick
- devised an experiment to prove the existence of neutrons
Different sub-atomic particles
- nucleons = protons + neutrons
- electrons
Properties of subatomic particles
- proton
- neutron
- electron
Isotopes
- Atoms with the same number of protons and electrons but different number of neutrons
- They have the same atomic number but a different mass number
- the reactivity of isotopes are identical as they have the same number of electrons
Atomic number
The number of protons
Mass number
Total number of protons an neutrons
What affects the reactivity of an element
The number of electrons
Equation for RAM
Ar = sum of the abundance x atomic number / total number of abundance
Relative atomic mass (RAM) (Ar)
The relative atomic mass is the average mass of its atoms compared to 1/12 the mass of a carbon-12 atom
Calculate the abundance of the different Chlorine molecules
Different stages of TOF
- Ionisation
- Acceleration
- Flight Tube (Ion drift)
- Detection
Stage 1 Ionisation for elements and low Mr compounds
- for ionisation to colour it has to be a gas
- high energy electron are fired by an electron gun
- this knocks out an electron of each particle
- the particle becomes a positive ion
Stage 1 Ionisation for high Mr compounds
- ionisation is in an aqueous solution (sample in a volatile solvent)
- passed through a hypodermic needle attached to positive terminal of high voltage power supply
- the particle gains a proton
Equation for Stage 1 elements and low Mr
equation for stage 1 ionisation with high Mr compounds
Stage 2 acceleration
- the positive ions are accelerated by using an electric field
- the ions are accelerate so that they have the same kinetic energy
Stage 3 flight tube (ion drift)
- particles have the same kinetic energy
- ions with a smaller mass will travel faster along the tube
Stage 4 detection (3 marks)
- positive ions hit the negative plate and produce and electric current
- the electrons move from the plate to the ion
- the size of current is proportional to the number of ions
Equations for TOF
KE = 1/2mv^2 t = d/v
Two types of ionisation
Electron impact (gun) Electrospray (needle)
How to calculate the mass of an ion
1 mole of Mass of element/1000 to get into kg
Then ANS/6.022x10^23 To get mass of 1 ion in kg
What is a species
- atom or molecules
Why is there a small peak at the Mr+1
What are the different orbitals?
s, p, d, f
How many electrons can an s orbital hold
2
How many electrons can a p orbital hold
6
How many electrons can be held on a d orbital
10
Electronic configuration of Chromium
[Ar} 4s1 3d5
Not [Ar] 4s2 3d4
Electronic Configuration of copper
[Ar] 4s1 3d10
Not [Ar] 4s2 3d9
What is the first ionisation energy
- this is the energy needed to remove one mole of electrons from
- one mole of atoms in their gaseous state
- to form one mole of 1+ ions (also in their gaseous state)
Ionisation energy down a group
- ionisation energy decreases
- atomic radius increases
- more shells/shielding
- weaker attraction between nucleus and OUTER electron
Equation for first ionisation, second ionisation energy…
General trend of ionisation energy across a period
- increases
- smaller atomic radius
- more protons
- stronger forces of attraction between nucleus and OUTER electron
- same shielding/ same shells
Why does going from group two to three dip in ionisation energy
- going to a different sub shell, eg 2s to 2p and p is a higher energy than s
- the distance is further away
- so the forces of attraction is weaker between nucleus and electron
- less energy required to remove the electron
Why does it dip from group 5 to group 6 in ionisation energy
- there is an electron pair repulsion
- p e- from orbital with one e-
- s e- from orbital with two e-
- there is more electron electron repulsion in s
Successive ionisation energy
- atoms with more than one electron can have them successfully removed
Second ionisation energy
- the energy required to remove one mole of electrons
- from one mole of gaseous unipostive ions
- to form one mole of gaseous dispositive ions
Trend of successive ionisation energy
- increases as the electron is being pulled away from a more positive species
A large increase occurs when there is a change of shell because there is a big decrease in shielding - large increases can be used to predict the group of an unknown element
What does it mean if there is a really big number jump in successive ionisation energy
This shows which group the element is in
