Atomic structure Flashcards
What did Democritus discover about atoms and when?
-They were indivisible particles in a spherical shape
-430 bce
What did John Dalton discover about atoms and when?
-All matter was composed of atoms (indivisible building blocks)
-Different elements had different sized atoms
1803
What did JJ Thompson discover about the atom and when?
-Atoms contained negatively charged particles (electrons)
-Ball of positive charge with electrons embedded inside
-Plum pudding model
1897
What experiment did Rutherford do relating to the atom?
-Gold foil experiment
-Fired positively charged alpha particles through foil
What were the results of Rutherford’s alpha scattering experiment?
-Most passed straight through the foil but some deflected back
Who’s model did Rutherford prove wrong and when?
JJ Thompson’s plum pudding model in 1911
What did Niels Bohr discover about the atom and when?
-Electrons orbited the nucleus at different fixed energy levels called shells
-They spiralled down into the nucleus causing it to collapse
1913
What is the refined Bohr model?
-Scientists discovered that not all electrons in the same shell had the same energy levels
-Added sub shells
-Explained why some elements are inert
What did Bohr believe about electron shells and elements reactivity?
-They can only hold a fixed number of electrons
-Reactivity is due to the elements electrons so if the shell is full the element is inert
What did James Chadwick discover and when?
The existence of neutrons in 1932
What is the relative mass of protons, neutrons and electrons?
proton-1
neutron- 1
electron-1/1840
What is the relative charge of protons, neutrons and electrons?
protons- +1
neutron- 0
electron- -1
Why is the reactivity of different isotopes of an element identical?
they have the same number of electrons
What is the share of percentages of isotopes of chlorine?
75% chlorine-35
25% chlorine- 37
How many protons and electrons do isotopes of carbon have?
6 protons and so 6 electrons
Define relative atomic mass:
the average mass of its atoms, compared to 1/12 the mass of a carbon -12 atom
What are the key steps in a time of flight mass spectrometer?
- Ionisation
- Acceleration
- Ion Drift
- Detection
What happens during ionisation?
-The sample is ionised to enter the mass spectrometer
-Ionisation- the atom loses an electron and forms a 1+ positive charge
What are the two methods of ionisation?
- Electrospray ionisation
- Electron impact ionisation
What happens during electrospray ionisation?
- Sample is dissolved in solvent
- pushed through small nozzle at high pressure
- A high voltage applied - gains H+ ions and increases mass by 1
- Solvent is removed - leaves gas made of positive ions
What happens during electron impact ionisation?
- Sample is vaporized
- Electron gun used to fire HIGH ENERGY electrons at it
- this knocks off one electron off one each particle - becomes +1 ions
What happens during acceleration?
- Positive ions are reflected by an electric field.
- Electric field gives the same kinetic energy to all ions.
- The lighter ions experience a greater acceleration
What happens during ion drift?
- The ions enter a region with no electric field
- They drift through it at the same speed as they left the electric field.
- Lighter ions will be drifting at high speeds
What happens during detection?
- Lighter ions reach the detector faster
- Data from detector (current and time of flight) is used to calculate mass/charge values needed to produce a mass spectrum
What does the detector measure?
The current created by ions and their time of flight.
What does the y-axis represent in a mass spectrum?
The abundance of ions as a percentage.
What does the height of each peak represent in a mass spectrum?
The relative isotopic abundance.
What does the x-axis represent in a mass spectrum?
The mass/charge (m/z) ratio
What is the relative isotopic abundance?
The amount of each isotope present in the sample
How is the mass/charge ratio of each peak related to the isotope’s mass?
The mass/charge ratio is equal to the relative mass of the isotope since each ion is +1 charged
What charge do ions have in a mass spectrometer?
Positive - mass spectrometer removes electrons
What unit is mass/charge often shown in?
M/z
What is first ionization energy?
Energy needed to remove one electron from each atom of an element in 1 mole of gaseous atoms, to form 1 mole of gaseous ions with a +1 charge
What are the factors affecting ionization energy?
- Nuclear charge : More protons = higher attraction
- Distance from Nucleus : Further electrons are easier to move
- Shielding : More inner electrons reduce the attraction to outer electrons
Why does each successive electron require more energy?
So they can be removed due to increased nuclear charge and reduce shielding
What is the general trend of 1st ionisation energy going down a group?
Decreases as you go down a group
Why does 1st ionisation energy decrease as you go down the group?
- atomic radius increases
- distance between the nucleus and outer electron increases
- shielding increases
THEREFORE the attraction between the nucleus and outer electron decreases, less energy required to remove the outer electron
What is the general trend of 1st ionisation energy across a period?
Increases across a period
Why does 1st ionisation energy increase as you go across a period?
- nuclear charge increases
-same shielding/ same distance of outer electron to nucleus
THEREFORE attraction between outer electron and nucleus increases, more energy needed to remove the outer electron
When going across a period, why is there an exception for the trend between groups 2 and 3?
Be/B and Mg/Al
it is easier to remove due to shielding by full ‘s’ orbital (higher energy levels)
When going across a period, why is there an exception for the trend between groups 5 and 6?
N/O and P/S
it is easier to remove due to electron pair repulsion
What is successive ionisation energies?
the energy required to remove electrons one by one from the same atoms
What are the equations for 2nd and 3rd ionisation energies?
Why is there a general increase in ionisation energy (successive ionisation energies)?
Due to increasing effective charge on the nucleus
Why are there large ‘jumps’ on the successive ionisation energies graphs?
Caused by electrons being taken from an energy level that is closer to the nucleus ie. decreased distance + decreased shielding THEREFORE stronger attraction
