the same wavelength leading to reinforcement (if
'in-phase') or attenuation (if 'out of phase'). See
Figure 5.3.1(b) and (c).
Interstitial Situated in cavities between larger atoms
or ions in a regular crystal structure.
Invariant Describes a point in a phase diagram that
has zero variance F (see discussion of Figure 2.1).
Inversion Recrystallization of a crystalline phase to a
more stable polymorph.
Ion Atom with a net electrical charge, due to the acqui-
sition or loss of electron (s). See anion and cation.
Ion pair Temporary electrostatic association in solu-
tion of two ions of opposite charge.
Ionic potential Ratio of an ion's nominal charge over
its ionic radius.
Isotropic Describes a substance whose physical
properties have values that are independent of the
direction in which they are measured.
Kelvin, K Unit of temperature expressed on the
absolute temperature scale. T /K = T /˚C + 273.15.
The kelvin (K) and degree Celsius (˚C) have the
same magnitude but differ in their zero points
(absolute zero and the melting point of ice
Kilobar (kbar, kb) 1 kb = 10 8 Pa. See bar .
Kiloelectron-volt (keV) 1000 electron-volts.
Kinetic energy ( E k ) The energy a body possesses by
virtue of its motion. See Chapter 1.
I = ∑
mz , a measure of how far an
Lanthanide One of the 14 elements following lantha-
num in the Periodic Table, characterized by the entry
of electrons into the 4f orbitals.
Latent heat of fusion The enthalpy required to trans-
form 1 kg of a solid completely into a liquid at constant
temperature (J kg −1 )
Latent heat of vaporization The enthalpy required
to transform 1 kg of a liquid into a gas at constant
temperature (J kg −1 )
Ligand (in a co-ordination complex or crystal) The
ions or molecules surrounding the central ion
or atom. For example in the dissolved complex
Cu(HS) 2 − , the ligands are the two HS − anions attached
to the central Cu + ion.
Linear A relationship between y and x is said to be
linear if plotting y against x yields a straight line.
Liquidus The temperature at which the first crystals
begin to form in a cooling melt. A liquidus curve (or
surface) shows the variation of liquidus temperature
with composition or with pressure.
Logarithm (log, ln) The magnitude of a number
expressed as a power of 10 (log 10 ) or of e (natural
logarithm = ln), as explained in Appendix A.
Lone pair Paired valence electrons in a filled lobe of
(usually) a hybrid orbital (e.g. Figure 7.5b, c). Lone
pairs influence hybrid shape, and are involved as
electron donors in the formation of co-ordination
ionic solution departs from ideal solution behav-
iour. I = ionic strength, m i = molality of ion species i ,
z i = charge on ion species i . See Appendix D for
explanation of Σ.
Ionization energy The energy (in eV or kJ mol −1 )
required to remove the most easily detached electron
from an atom to a state of rest at infinity (Figure 5.6).
Ionization potential Obsolete synonym for ioniza-
tion energy .
Iso- Prefix meaning 'having the same …' .
Isobar, isobaric (a) A pressure 'contour', a hypotheti-
cal line or surface in P-T-X space at which pressure
is everywhere uniform. 'Isobaric' signifies a process
that occurs at constant pressure. (b) Nuclide having
the same mass number A (Box 6.1) as another.
Isochron A line on an isotope-ratio plot drawn
through data points having the same age.
Isotherm, isothermal A temperature contour in a
phase diagram. A line or surface on which tempera-
ture is constant. 'Isothermal' signifies a process
operating (or a phase diagram constructed) at con-
Isotone See Box 10.1.
Isotope An isotope of an element consists of nuclei
that share the same values of atomic number Z and
neutron number N . Other isotopes of the element
have the same value of Z but different value(s) of N .
See Box 10.1.
Isotopic tracer An isotopic ratio differing between
one type of source material and another, that indi-
cates the derivation of a rock or solution.
Macroscopic Visible to the naked eye or measurable
with normal laboratory apparatus, as opposed to