AS Live Session Spring 2024
Mrs Nerys Stephens�Chemistry Teacher and �Head of Years 9, 10 & 11� Ysgol Bro Pedr
Spring 2024 AS Sessions:
Session 1 – Radioactivity and Ionisation Energies (NS)
Session 2 – Gravimetric Practical (PB)
Session 3 – Instrumental Analysis (NS)
Session 4 – Making up a Standard Solution and Titrations (PB)
Radioactivity
and
Ionisation Energies
(AS Chemistry)
RADIOACTIVE EMISSION
Alpha (α) particles
Alpha particles are made of two protons and two neutrons that are ejected from the nucleus at high speed. Alpha particles can also be described as helium nuclei 42He2+.
Beta (β) particles
Beta particles are electrons (0-1e) that are ejected from the nucleus at high speed.
RADIOACTIVE EMISSION
Positrons (β+)
Positrons are anti-electrons (01e) that are ejected from the nucleus at high speed. An anti-electron has the same mass as an electron but a different electrical charge: positive.
When a positron comes into contact with an electron, they obliterate each other and create gamma radiation
RADIOACTIVE EMISSION
Gamma (γ) radiation
Gamma radiation is high energy electromagnetic radiation. Gamma radiation is emitted when a heavy nucleus rearranges itself into a more stable configuration.
Gamma radiation is also emitted after a process called electron capture. Electron capture occurs when a proton-rich nucleus absorbs an inner electron. This electron combines with a proton to form a neutron.
Nuclear Equations
It is very important that you understand the effect that radioactive emission has on the mass and atomic number of the atom that emits it.
When an alpha particle is emitted, the new atom formed has a mass number 4 lower and an atomic number 2 lower than the original atom:
Nuclear Equations
It is very important that you understand the effect that radioactive emission has on the mass and atomic number of the atom that emits it.
When a beta particle is emitted, the new atom formed has an atomic number 1 higher than the original atom because a neutron is changed into a proton. The mass number is unchanged:
Nuclear Equations
It is very important that you understand the effect that radioactive emission has on the mass and atomic number of the atom that emits it.
When a positron is emitted, the new atom formed has an atomic number 1 lower than the original atom because a proton is changed into a neutron. The mass number is unchanged
He
Ne
Ar
Kr
Xe
1st Ionisation Energy values show a periodic trend. There is a ‘general increase’ across a period before the value drops dramatically for the start of another period.
The values get smaller down groups as the electron removed comes from an orbital further from the nucleus - there is more shielding.
Variation in 1st Ionisation Energy - PERIODS
1s 2s 2p
1s 2s
1s 2s
1s
1s
ATOMIC NUMBER
1st IONISATION ENERGY / kJmol-1
EXPLANATION
There is a DROP in the value for Boron. This is because the extra electron has gone into one of the 2p orbitals. The increased shielding makes the electron easier to remove
It was evidence such as this that confirmed the existence of sub-shells. If there hadn’t been any sub-shell, the value would have been higher than that of Beryllium.
Variation in 1st Ionisation Energy
BORON
5
1s 2s 2p
1s 2s 2p
1s 2s 2p
1s 2s 2p
1s 2s
1s 2s
1s
1s
ATOMIC NUMBER
1st IONISATION ENERGY / kJmol-1
Variation in 1st Ionisation Energy
EXPLANATION
There is a DROP in the value for Oxygen. The extra electron has paired up with one of the electrons already in one of the 2p orbitals. The repulsive force beteen the two paired-up electrons means that less energy is required to remove one of them.
OXYGEN
8
Successive Ionisation Energies
Atoms with more than one electron can have them successively removed.
2nd I.E. The energy required to remove one mole of electrons (to infinity) from one mole
of gaseous unipositive ions to form one mole of gaseous dipositive ions.
e.g. Na+(g) Na2+(g) + e-
Al+(g) Al2+(g) + e-
Trends Successive ionisation energies are always greater than the previous one
Reason :- the electron is being pulled away from a more positive species
Large increases occur when there is a change of shell
Reason :- there is a big decrease in shielding
Large increases can be used to predict the group of an unknown element
Again, make sure you write in the (g)
Additional Past Paper Questions.
Instrumental Analysis
(Topic 2.8)
(AS Chemistry)
Use of Mass Spectra and IR in structure identification ��
Use of Low resolution 1H NMR and 13C NMR in structure identification�
A Typical Exam Question:
- to test your understanding
It is always sensible to address the evidence in the order in which it has been provided.
Therefore, start by using the supplied information regarding the test for a halogenoalkane
Following this, use the supplied information to calculate the empirical formula.
Following this, look at the next piece of evidence, suggesting the presence of unsaturation.
The mass spectrum states that A has a molecular mass of 123.
Therefore, 123g of A equates to 1 mol.
Following this, look at the 1H and 13C NMR evidence.
Following this, look at the IR spectrum.
Following this, look at the Mass spectrum.
Putting all the evidence together:
And another exam question….
Putting all the evidence together:
CH3-CO- → expected in the region of 2 – 2.5, with a height of 3
-CH2-CO- → expected in the region of 2 – 3, with a height of 2
CH3- → expected in the region of 0.1 – 2, with a height of 3