3.1.1 Atomic structure Flashcards
Developing the idea of the atom
1661 - boyle proposed no substances smaller
1803 - dalton elements composed of spheres called atoms
1897 - JJ thompson - electrons
1911 - rutherford small pos nucleus in the middle
Gold foil experiment
Fire alpha radiation at gold foil
5. 1913 - bohr electrons in shell6. 1932 - chadwick discovers the neutron
Forces in the nucleus
Strong nuclear forces - protons and neutrons together
Electrostatic forces - electrons and protons
Uses for the scientists model
Daltons model - explain the geometry of crystals
Bohr’s model - ionic and covalent
Electrons orbiting in shells - bonding
TOF Mass spectrometer
Used to find out relative atomic masses
Mass spectra identify different isotopes that make up an element
Happens in a vacuum
1. Vaporization
dissolved in a volatile solvent
2. Ionization
2.. Acceleration
3. Ion drift
4. Detection
5. Data analysis
Signal passed to a computer which generates mass spectra
High resolution mass spectrometry
Atomic masses up to 5dp
Low resolution - 1dp
What is the m/z value
Mass / charge ratio
TOF electrospray ionization
- Electrospray Ionisation
o This method is used for substances which have a higher molecular mass
. fragmentation is unlikely to happen
o For this method, the sample is dissolved in a volatile solvent
o The solvent is injected into the mass spectrometer using a hypodermic needle
This produces a fine mist or aerosol
o The needle is attached to a high voltage power supply, so as the sample is injected, the particles are ionised by gaining a proton from the solvent
X (g) + H+ → XH+ (g)
Using mass spectrometer to calculate relative atomic mass of an element
= (abundance x m/z) + (abundance x m/z) / 100
Electron configuration
Shell - subshell - orbits
4s, 3d
4s is a lower energy than 3d - so fills first
Electrons into atomic orbitals Rules
Atomic orbitals of lower energy are filled first
Orbitals fill singularly before doubling up - as they repel each others in orbitals
No orbitals more than two electrons
Ionization energy
The energy required to remove a mole of electrons from a mole of atoms in gaseous state
Measured in KJmol-1
Elected by
Shielding
Atomic charge
Atomic size
Succession ionization energies
first electron - needs the least energy to remove it as being removed from a neutral atom
Second electrons - need more energy as removed from a 1+ ion
And so on
come from the 4s before the 3d as more shielding so takes less energy
Trends in ionization energies down a group
Decreases
Ar increases
Shielding
Trends in ionisation energy along a period
Increases across
More protons increased nuclear charge
Shielding is similar across
Ionization energy exceptions
Aluminium - slightly higher energy in subshell - slightly further from the nucleus than in magnesium
Sulphur - electron repulsion - taken from full orbital - repel less energy needed - shielding the same
Anomalies in energy level diagrams
Chromium + copper - half full 4s - creates a more stable half full orbital
the ion that reaches the detector first in TOF
make sure to write charge the lightest m/z
medical use for magmesium hydroxide
intergrestion relife
Sub atomic particles
Protons - 1, +1
Electrons -1 , 1/2000
Neutrons 1,0
Proton number and mass number
Protons in the nucleus is called the atomic number
Number of protons + number of neutrons
Isotopes
Same number of protons and same number of electrons different number of neutrons
React chemically the same way - same el
ectron configuration
Vary in mass number
Electron shells
2,8,8,18
Stage 2: Acceleration
Stage 2: Acceleration
* They are all accelerated to have the same kinetic energy
o This is important for you to remember when completing calculations
* Since all 1+ ions will have the same kinetic energy, their velocity will depend on their mass
o Lighter ions will move faster and heavier ions will move slower
Stage 3: Ion Drift (in the flight tube)
The 1+ ions will pass through a hole in the negatively charged plate and move into a flight tube
Stage 4: Detection
- Once they have pass through the mass spectrometer, the 1+ ions will hit a negatively charged ‘detector’ plate
- As they hit this electric plate, they gain an electron
- This gaining of an electron discharges the ion, and causes a current to be produced
o This size of the current is proportional to the abundance of those ions hitting the plate and gaining an electron
TOF electron impact ionization
Electron Impact Ionisation
* This method of ionisation is used for elements and substances which have a lower molecular mass
* The sample is vaporised and then bombarded with high energy electrons
* The electrons are ‘fired’ from an electron gun
o The electron gun is a hot wire filament which emits electrons as a current runs through it
* As the sample is bombarded by these electrons, an electron is knocked off each particle, forming a 1+ ion
peaks on a TOF graph
- The peak with the highest mass is the molecular ion peak, M+, and the peak which has the largest abundance (tallest peak) is called the base peak
