Concise and comprehensive notes available for the biology and chemistry sections of the new ESAT specification. For Cambridge Natural Sciences applicants. Written by alumni of the Cambridge Natural Sciences Tripos. Make sure you know all content so you only use the precious time available for each...
ESAT: Chemistry Notes
Concise and complete notes on all chemistry in the ESAT specification
1. Atomic structure
Atom
1. Central nucleus of protons and neutrons surrounded by electrons in energy levels
2. Most mass in nucleus
3. Volume of nucleus very small compared to volume of atom
4. Mostly empty space
5. Electrons in shells of increasing energy (1st shell: 2 electrons; 2nd shell 8 electrons; 3rd
shell: 18 electrons)
Proton: relative mass = 1, charge = +1
Neutron: relative mass = 1, charge = 0
Electron: relative mass = 0 (negligible), charge = -1
Atomic Number: number of protons in the nucleus (and number of electrons in neutral atom)
Mass Number: sum of protons and neutrons in the nucleus
Isotopes: atoms of the same element with the same number of protons but different number
of neutrons
Mass spectrometry
1. Used to determine relative abundance and mass of different chemical species, such as
isotopes
2. Mass spectrum: relative abundance on y-axis; mass/charge (m/z) on x-axis
3. Mass/charge = mass (if z = +1); assume z = +1 unless context suggests otherwise
4. Mass/charge x charge = mass (if z ≠+1)
Relative atomic mass (Ar): weighted average mass of an element’s isotopes compared to
1/12th mass of Carbon-12
(abundance of isotope 1 × Ar of isotope 1) + (abundance of isotope 2 × Ar of isotope 2) + …
Ar =
total abundance
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