(🟠 TOPIC 1) Key Definitions … Flashcards
Atomic number (z)
The number of protons in the nucleus of an atom of a certain element
Mass number (A)
The sum of the number of protons and the number of neutrons in the nucleus of an atom of a certain element
Isotopes
An atom of the same element with the same number of protons, but a different number of neutrons, therefore a different mass number
(Isotopes of the same element have identical chemical properties because they have identical electronic configurations)
Relative atomic mass (Ar)
The weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12 which has a mass of 12
Relative isotopic mass
The mass of an atom of an isotope of an element relative to 1/12th of the mass of an atom of carbon-12 which has a mass of 12
m/z
Mass to charge ratio
In mass spectrometry, nearly all ions will have lost one electron, making them +1 ions, but …
If a 2+ ion is formed, m/z = m/+2, so the m/z value is halved
Molecular ion peak (/parent ion peak)
The peak with the highest m/z ratio in the mass spectrum (the M peak). This gives the Mr of the whole molecule.
(It is the last peak (apart from the M+1 peak if visible - very small))
However, the molecular ion peak is also sometimes quite small
Orbital
A region of space within an atom where there is a high probability of finding an electron. It can hold up to two electrons with opposite spins.
(Orbitals increase in size as they move further away from the nucleus (higher quantum shells))
Aufbau Principle
Type of electronic configuration notation (s,p,d,f)
Subshells of lowest energy are filled first
Hund’s Rule
States that electrons will occupy the orbitals singly before pairing takes place.
Type of electronic configuration notation (s,px,py,pz…)
(Eg. P orbital on the x-plane/ axis)
Pauli Exclusion Principle (box notation)
States that two electrons cannot occupy the same orbital unless they have opposite spins.
Type of electronic configuration notation (boxes with half arrows - up,down)
Periodicity
The repeated trend in properties across a period
(Electronic configurations, atomic radii, melting + boiling temperatures, first ionisation energy)
Atomic radius
Distance from centre of nucleus to boundary of electron cloud
Quantum shell
Defines the energy level of an electron.
Electrons in the first quantum shell/energy level have the lowest energy (energy of electrons increases as they go further away from the nucleus)
S-block element
Has highest energy electron in an s-orbital
P-block element
Has highest energy electron in a p-orbital
D-block element
The d-sub shell is being filled
(Cannot be defined in same way as other blocks as the 4s subshell will be filled before the 3d subshell, so has more energy than the 3d subshell. Therefore the highest energy electron is not in the d subshell)
What’s the difference between relative molecular mass and relative formula mass?
Relative molecular mass is the sum of Mr of simple molecules (eg. N2, H2SO4)
Relative formula mass is the sum of Mr of compounds with giant structures (eg. Pb(NO3)2)
M+1 peak
A very small peak that sometimes occurs after the M-peak - caused by the presence of carbon-13 (isotopes)
Base peak
The tallest peak, the most abundant molecule/atom in a sample
Isomer
Compounds with the same molecular formula but with a different arrangement of atoms in the molecule and different properties
Geometric isomerism
Compounds with a C=C double bond with atoms/ groups attached to it at different positions (E/Z, cis/trans)
Crude oil
A mixture of mostly alkanes of different chain lengths and therefore different boiling points
Cracking
The process of breaking excess heavier hydrocarbons into smaller, more useful compounds
Large alkane —> Smaller alkane + alkene (with aluminium oxide catalyst Al2O3)
