Atomic Structure Flashcards
Describe the development of the atom.
Democritus - claimed atoms couldn’t be split
John Dalton - determined atoms were tiny particles (hold spheres that couldn’t be split) which made up elements.
J.J. Thomson - Discovery of electrons and proof that could be split
Rutherford - Developed nuclear model (mass concentrated in centre and electrons in shell orbiting)
James Chadwick - Experiment showed existence of neutrons
Name the 3 sub-atomic particles.
Protons, neutrons and electrons
What is the relative mass and charge of a proton?
Relative Mass = 1
Relative Charge = +1
What is the relative mass and charge of an electron?
Relative Mass = 1/1840
Relative Charge = -1
What is the relative mass and charge of a neutron?
Relative Mass = 1
Relative Charge = 0
What is the mass number?
Number of protons and neutrons.
What is the atomic number?
The number of protons.
What is an isotope?
Atoms with the same number of protons but different number of neutrons.
The mass number is different because of the different number of neutrons
What is different about the reactivity of isotopes?
They react chemically the same because of the same electron configuration.
What is time of mass spectrometry?
Powerful instrument method of analysis.
It can be used for:
- Finding the abundance and mass of each isotope in an element allowing us to determine its relative atomic mass
-Find the relative molecular mass of substances made of molecules
What is a common form of mass spectrometry?
Time of flight spectrometry - particles of the substance are ionised to form +1 ions which are accelerated so they all have the same kinetic energy. The time to travel a fixed distance is then used to find the mass of each ion in the sample
What is the name of the first stage and name the two techniques?
Ionisation - Electron Impact & Electrospray
Describe electron impact.
- Sample is vaporised to a gas
- High energy electrons fired at it from an electron gun
- Electron gun is hot wire filament with current running through it that emits electrons
- Usually knock off one electron from each particle forming a 1+ ion.
- 1+ ions then attracted towards a negative electric plate where they are accelerated
What is the electron impact used for?
Elements and substances with low formula mass (can be inorganic and organic)
Describe the electrospray ionisation.
- Sample dissolved in a volatile substance
- Injected through fine hypodermic needle giving a fine mist/ aerosol
- Tip of needle attached to positive terminal of high voltage supply
- Particles are ionised by gaining a proton as it leaves the needle
- Solvent evaporates whilst ions are attracted towards negative plate where they’re accelerated
What is the second stage of time flight spectrometry?
Acceleration
Describe acceleration
- Positive ions accelerated using an electric field so that they all have the same kinetic energy
- The velocity of each particle depends on its mass.
- Lighter particles have faster velocity and heavier particles have a slower velocity
What is the third stage of time flight and spectrometry and describe it?
Flight tube
- Positive ions travel through a hole in the negatively charged plate into a tube.
- ToF of each particle through this flight tube depends on its velocity which in turn depends on its mass (lighter = faster , heavier = slower)
What is the fourth stage of time flight spectrometry and describe it?
Detection
- +tive ions hit negatively charged electric plate.
- When hitting the detector plate, positive ions are discharged by gaining electrons from the plate.
- Generates movement of electrons hence an electric current is measured.
- Size of the current gives a measure of the number of ions hitting the plate
What is the mass spectrum?
- A computer uses data to produce the mass spectrum.
- It shows the mass to charge (m/z) ratio and abundance of each ion that reaches the detector.
- m/z effectively the mass of each ion
Why may there be peaks at lower m/z values?
Due to fragments caused by the break up of molecular ion
How many electrons can fit on a s-sub-level?
2
How many electrons can fit on a p-sub-level?
6
How many electrons can fit on a d-sub-level?
10
