Atomic Structure Flashcards
Mass Number
Number of protons/electrons
Atomic Number
Number of protons
Proton
- Charge: +1
- Mass: 1
Neutron
- Charge: 0
- Relative Mass: 1
Electron
- Charge: -1
- Mass: 1/1836
Isotopes
Atoms of an element with the same number of protons but a different number of electrons
Structure of the Atom
- Mostly empty space
- Small nucleus in the centre
- Nucleus is made up of protons and neutrons, is positively charged and has a radius of 1x10^-14
Relative Atomic Mass
Total mass of atoms/Total number of atoms
Robert Boyle
- 1662
- Proposed there were some substances that couldn’t be made simpler
John Dalton
- 1803
- Suggested elements were made of invisible atoms that can’t be broken down
Henri Becquerel
- 1896
- Discovered radioactivity showing that particles could come from inside the atom (decay)
JJ Thompson
- 1897
- Discovered the electron
- Proposed the plum pudding model
Ernest Rutherford
- 1911
- Suggested the atom was mostly empty space with a dense nucleus containing the positive charge
- Suggested the nuclear model
- Discovered the proton
Geiger and Marsden
- 1908-1913
- Conducted the gold foil experiment which showed the atom was mostly empty space
Niels Bohr
- 1913
- Suggested electrons orbit the nucleus in shells that are at regular distances from the nucleus
James Chadwick
- 1932
- Discovered the neutron
Mass Spectrometry
Used to determine the elemental and isotopic composition of a sample
Electrospray Ionisation
- The sample is dissolved in a volatile solution
- The solution is forced through a fine hollow needle connected to the positive terminal of a power supply
- This produces tiny positively charged droplets which have lost electrons to the positive charge supply
Electron Impact Ionisation
- The sample is vapourised and high energy electrons are fired at it using an electron gun
- This knocks off an electron from the sample forming a 1+ ion
Mass Spectrometry: Ionisation
- All the different isotopes of an element are placed in a sample chamber
- Atoms are all ionised and converted to positive ions
Mass Spectrometry: Acceleration
- Positively charged ions become attracted to a negatively charged plate
- This causes the ions to accelerate which increases the kinetic energy of the ions
- Ions with the same charge have the same kinetic energy
Mass Spectrometry: Ionic Drift
- When the ions pass through the plate they stop accelerating and drift down the chamber toward the detector
- Lighter ions move faster towards the detector than heavier ions
- As a result they reach the detector first
Mass Spectrometry: Detection
- The positive ions gain electrons at the detector
- Electron transfer causes current to flow
Why is the interior of a mass spectrometer a vacuum?
To prevent ions from colliding with molecules in the air
How can you tell the Mass of an Isotope?
Finding out the time it took for the ions of a sample to reach the detector
How can you tell the abundance of an Isotope?
- Find out the size of the current produced when each isotope hits the detector
- A more abundant isotope produces a greater current
Mass Equation
(Ar/1000) x moles (Avogadro’s Constant)
