Keywords / Terms / Definitions
atomic number (Z)
number of protons in the nucleus of an atom. Unique to each element.
mass number (A)
number of protons plus the number of neutrons in the nucleus of an atom
nucleon
collective term for protons and neutrons
Relative atomic
mass
the weighted average mass of all the naturally occurring isotopes of an element compared with an
atom of the C-12 isotope, which has a mass of exactly 12
mass
spectrometer
instrument for determining relative atomic masses and relative molecular masses
isotopes
atoms of an element with different numbers of neutrons; same atomic number, different mass
numbers
ionize
to remove an electron from a gaseous atom
valence shell
outermost shell, highest main energy level
valence electron
electron in the highest main energy level
Planck’s constant
(h)
a constant which connects the energy of radiation with the frequency of radiation, E=hf, (h= 6.63
× 10-34 J s, given in the data booklet)
continuous
spectrum
spectrum such as ‘white’ light with all the frequencies and no gaps (looks like a rainbow)
line spectrum
spectrum with bright lines of specific colours at specific frequencies, with black spaces in between
emission spectrum
characteristic line spectrum for a particular element
Alan Forster
frequency (of
electromagnetic
radiation)
number of complete waves passing any point per second; unit = Hertz (Hz)
quantum
"package" of energy released by an electron as it drops back to a lower energy level
photon
a quantum of light energy
convergence (of
lines/energy
levels)
lines or energy levels getting closer together. This happens at higher frequencies (higher
energies)
n
"principal quantum number"- notation to represent the main energy levels in an atom; n =1 is the
lowest energy level
sub-levels
levels within the main energy levels; each sub-level is divided into orbitals, e.g. 2p:
2 is the principle energy level, p is the sublevel, and it contains three orbitals: 2p x, 2py and 2pz
excited state
state of an atom or molecule when one or more of its electrons is raised to a higher energy above
the stable ground state. Heat, electricity or electromagnetic radiation can excite the atoms or
molecules.
electron
configuration
a detailed representation of electron arrangement, showing sub-levels within the principle energy
levels, e.g. Li 1s2 2s1
orbitals
regions of space where there is high probability of finding an electron; each orbital represents a
discrete energy level and can hold a maximum of 2 electrons
s orbital
spherical orbital in s-sub-level
p orbital
one of three dumb-bell shaped orbitals in a p sub-level
degenerate
orbitals
equal energy orbitals
Alan Forster
spin
property of electrons which accounts for their behavior in a magnetic field; an atomic orbital can
hold two electrons with opposite spins (+1/2 or -1/2)
Heisenberg
Uncertainty
Principle
Principle that states that it is impossible to know the exact location and momentum of an electron
Pauli Exclusion
Principle
Principle that states that no 2 electrons in the same atom can have the same 4 quantum numbers
(i.e. 2 electrons in the same orbital must have opposite spin) – each electron is unique!
Aufbau Principle
Principle that states that the lowest energy levels are always filled first
Hund's Rule
Rule that states that electrons occupy orbitals of equal energy singly, before they will pair up
(maximum multiplicity) – analogy is people going on a bus and sitting on their own rather than
sitting beside a stranger
Keywords / Terms / Definitions - Higher Level
first ionization energy
the energy required to remove 1mole of electrons from 1mole of gaseous atoms
e.g.
Na(g) à Na+(g) + eDHIE = +494 kJmol-1
second ionization
energy
the energy required to remove 1mole of electrons from 1mole of gaseous 1+ charged cations
e.g.
Na+(g) à Na2+(g) + eDHIE2 = +4564 kJmol-1
shielding effect
shielding electrons are the electrons in the energy levels between the nucleus and the outer or
valence electrons, described as ‘shielding’ electrons because they ‘shield’ the valence electrons
from the nuclear charge and reduce the attractive force on them by the protons in the nucleus
convergence limit
the point in a line emission spectrum where the lines merge to form a continuum; may be used to
determine the ionization energy
Alan Forster