Topic 1 - ATOMIC STRUCTURE
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Definition of Atomic number
The number of protons in the nucleus of an atom
Definition of Mass number
The total number of protons and neutrons in the nucleus of an atom
Definition of Relative isotopic mass (RIM)
The mass of an atom of a particular isotope of an element, relative to 1/12th the mass of a carbon-12 atom
Definition of Relative atomic mass (RAM)
The average mass of an atom of an element, relative to 1/12th the mass of a carbon-12 atom
Definition of Relative molecular mass (RMM)
The average mass of a molecule of a substance, relative to 1/12th the mass of a carbon-12 atom
Definition of Relative formula mass (RFM)
The average mass of a formula unit of a substance, relative to 1/12th the mass of a carbon-12 atom
Definition of isotopes
Isotopes are atoms of the same element, with the same number of protons but different number of neutrons.
What are the stages of a mass spectrometer?
Vaporisation, ionisation, acceleration, deflection and detection
What happens during vaporisation in a mass spectrometer?
The sample is turned into a gas
What happens during ionisation in a mass spectrometer?
The sample is turned into an ion - high speed electrons are shot out from an electron gun, bombarding the gaseous sample until it loses an electron, becoming a positively charged ion.
What happens during acceleration in a mass spectrometer?
Particles are accelerated by an electric field
What happens during deflection in a mass spectrometer?
An electromagnet creates a magnetic field that deflects the ions. - Mass and charge affects deflection
Definition of first ionisation energy
First ionisation energy is the energy required to remove one electron from each atom in one mole of gaseous atoms
Definition of second ionisation energy
Second ionisation energy is the energy required to remove one electron from each 1+ ion, in a mole of gaseous ions.
How does number of protons influence ionisation energy?
• The more protons in the nucleus, the higher the nuclear charge • Hence the atomic radius is smaller (greater attraction) and more energy is needed to overcome this attraction
Why does it matter if an electron is by it-self or paired in an electron shell?
• Two electrons in the same orbital experience a bit of repulsion from each other • This offsets the attraction of the nucleus, so it is easier to lose an electron
How does electron shielding influence ionisation energy?
Electron shielding is the number of electron levels in an atom. The greater the shielding, the less energy needed to overcome the forces of attraction. The inner shells repel the outer shell electrons
How does the electron sub-shell influence ionisation energy?
The lower the electron sub-shell, the greater the energy needed to over come the forces of attraction.
Why is the first ionisation energy of aluminium less than magnesium?
The first ionisation energy of aluminium is less than that of magnesium because removing an electron from a higher energy orbital requires less energy. The electron removed from aluminium is in a 3p sub shell, which has a higher energy than the 3s electron in magnesium.
Why is the first ionisation energy of sulphur less than that of phosphorous?
The highest energy electron in both phosphorous and sulphur is the 3p sub-level, and sulphur has a higher nuclear charge. However, Sulphur has an electron that is spin-pairing, leading to repulsion of the two electrons.
What are orbitals?
Orbitals are a region of space within an atom where there is a probability of finding an electron
What is Pauli’s exclusion principle?
The electrons must have different spins in any orbital, 2 electrons max
What is the Aufbau process?
The electrons fill up the lowest empty energy levels
What is Hund’s rule?
We half fill the orbitals of the same energy with electrons of the same spin