3.1.1 Atomic Structure Flashcards
What was John Dalton’s model of the atom like? (2)
Solid spheres
Different spheres made up different elements
What was JJ Thomson’s model of the atom like? (2)
The ‘Plum Pudding’ Model
An atom contains smaller, negatively charged particles (electrons) surrounded by a positively charged ‘pudding’
What was Rutherford’s model of the atom like? (3)
A tiny, positively charged nucleus at the centre
A ‘cloud’ of negative electrons surrounding the nucleus
Most of the atom is empty space
What was Bohr’s model of the atom like? (3)
Electrons only exist in fixed orbits (shells)
Each shell has a fixed energy
When an electron moves between shells, electromagnetic radiation of fixed frequency is emitted or absorbed
What is the relative charge of a proton?
+1
How did the gold foil experiment disprove the plum pudding model?
They were expecting most of the alpha particles to be deflected slightly by the ‘pudding’ but most passed straight through the gold foil instead
Why was Rutherford’s model for the atom disproved?
If electrons were in a ‘cloud’ around the nucleus, they would quickly spiral down into the nucleus and the atom would collapse
What is the relative mass of a proton?
1
What is the relative charge of a neutron?
0
What is the relative mass of a neutron?
1
What is the relative charge of an electron?
-1
What is the relative mass of an electron?
1 / 2000
What does the letter A represent?
Mass number
What does the letter Z represent?
Atomic (proton) number
How is relative atomic mass calculated?
(Isotopic mass x percentages) / total percentage
How is relative molecular mass calculated?
Add up the relative atomic mass of all atoms in the molecule
What is the difference between relative molecular mass and relative formula mass? (2)
Relative formula mass is used on ionic and giant covalent compounds
Relative molecular mass is used used on other molecules
TOF Mass Spectrometry:
Concept (3)
Particles of a substance are ionised to form 1+ ions
They are accelerated so they have the same kinetic energy
The time taken to travel a fixed distance is used to find the mass of each ion in the sample
TOF Mass Spectrometry:
Uses (3)
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
Identify elements
TOF Mass Spectrometry:
Electron Impact / Electron Ionisation (4)
The sample is vaporised
An electron gun (a hot wire filament with a current that emits electrons) fires high energy electrons at the vaporised sample
This usually knocks off one electron from each particle, forming a 1+ ion known as a molecular ion
X(g) ➖ X+(g) + e-
TOF Mass Spectrometry: Electrospray Ionisation (3)
The sample is dissolved in a volatile solvent (e.g. water or methanol)
It is injected through a fine hypodermic needle attached to the positive terminal of a high-voltage power supply to give a fine mist (aerosol)
The particles gain a proton (H+) from the solvent as they leave the needle and the solvent evaporates away
X(g) + H+ ➖ XH+(g)
TOF Mass Spectrometry:
Which method of ionisation should be used? (2)
Electron impact is used for substances with a low formula mass (organic or inorganic)
Electrospray ionisation is used for substances with a higher molecular mass (including biological molecules) such as proteins
TOF Mass Spectrometry:
Fragmentation (2)
The molecular ion formed from electron impact often breaks down into smaller fragments which are also detected in the mass spectrum
Electrospray ionisation is a ‘soft’ technique so fragmentation rarely takes place
TOF Mass Spectrometry:
Acceleration (2)
The positive ions are accelerated using an electric field as they are attracted to a negative plate
The field gives the same kinetic energy to all of the ions
