Physical - Atomic Structure Flashcards
(27 cards)
When and what did Robert Boyle contribute to ideas of the atom
some substances could not be made simpler: now known as chemical elements.
When and what did John Dalton contribute to ideas of the atom?
Elements were composed of indivisible atoms. All the atoms of a particular element had the same mass. Other elements had different masses. Atoms could not be broken down.
When and what did Henri Becquerel contribute to ideas of the atom?
discovered radioactivity and thus disproved that atoms were divisible.
The following year J.J. Thomson discovered the electron. The electrons negative charge meant positively charged protons had to exist. Thomson developed the plum pudding model.
When and what did Ernest Rutherford contribute to ideas of the atom?
found that most of the mass and all the positive charge of the atom was in a tiny central nucleus.
When and what did Niels Bohr contribute to ideas of the atom?
atoms consist of a tiny positive nucleus orbited by electrons in shells of fixed size. Movement of electrons between shells explained how atoms absorb and give out light.
When and what did Erwin Schrödinger contribute to ideas about the atom?
worked out an equation which used the ideas that electrons have some properties of waves. Created quantum mechanics which can be used to predict the behaviour of subatomic particles.
When and what did James Chadwick contribute to ideas of the atom?
discovered the neutron.
Name the 3 subatomic particles and their relative charge and relative mass.
Protons - Relative Mass (1), Relative Charge (+1)
Neutrons - Relative Mass (1), Relative Charge (0)
Electrons - Relative Mass (1/1840), Relative Charge (-1)
Where are the protons and neutrons found in the atom? What holds them there?
In the nucleus, held by the nuclear strong force. This is much stronger than electrostatic forces of attraction so overcomes the repulsion of the positively charged protons.
Which subatomic particles are known as nucleons?
Protons and neutrons.
Which letter represents the atomic number?
Z
Which letter represents the mass number?
A
Explain the existence of isotopes.
All atoms of an element have the same number of protons.
However atoms of the same element can have varying numbers of neutrons.
This creates isotopes such as carbon-12, carbon-13, carbon-14.
They are all carbon because of their 6 protons but are isotopes due to their different numbers of neutrons and thus different mass numbers.
How many electrons can fit in the s sub-shell?
2 - 2 per orbital
How many electrons can fit in the p sub-shell?
6 - 2 per orbital
How many electrons can fit in the d sub-shell?
10 - 2 per orbital.
Define first ionisation energy.
Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form one mole of +1 ions. Measured in (KJ mole^-1)
Write an equation for the first ionisation energy of element X
X (g) —> X+(g)+ e-
Explain the trend in first ionisation energy across period 3. (Na-Ar)
-General increase due to increased nuclear charge and increased attraction between positive nucleus and negative electrons.
- Decrease in first IE between magnesium (1s2,2s2,2p6,3s2) and Aluminium (1s2,2s2,2p6,3s2,3p1)
This is because the outer electron is in the 3p orbital which is of slightly higher energy than the 3s orbital, therefore less energy is needed to remove it.
- There is also a small drop between Phosphorus (…3p3) and Sulfur (…3p4). In phosphorus each 3p orbital contains one electron. In Sulfur there is one pair of electrons in one 3p orbital. The repulsion from the other electron reduces the energy needed to remove it, despite increased nuclear charge.
- These deviations from the trend are evidence of s- and p-sub-levels.
Explain the trends in ionisation energies down group 2 (Be-Ba)
- General decrease going down the group because the outer electron is in a main level that gets further from the nucleus - more shielding, lower attraction between nucleus and electron.
- Increased nuclear charge does not increase ionisation energy due to the increased shielding.
What are the steps of Time of Flight (TOF) mass spectrometry?
- Ionisation
- Acceleration to the same kinetic energy
- Ion drift
- Ion detection
- Data analysis
Explain electron impact/bombardment ionisation.
- A vaporised sample is injected at low pressure.
- An electron gun fires high energy electrons at the sample.
- This knocks out an outer electron.
- This forms positive ions.
Explain electro spray ionisation.
- Sample is dissolved in a volatile, polar solvent, injected through a fine needle, giving a fine mist.
- The tip of the needle has a high voltage.
- At the tip of the needle, the sample molecule (M) gains a proton (H+) from the solvent forming MH+.
-M(g) + H+ -> MH+(g) - The solvent evaporates away and MH+ ions move towards a negative plate.
Describe the acceleration stage of TOF spectrometry.
- Positive ions are accelerated by an electric field.
- All ions are accelerated to the same kinetic energy.
- (Ek = 0.5mv2) so the velocity of each particle depends on its mass.
- Lighter particles have a higher velocity, heavier particles have a lower velocity.
