Chapter 8 -- Electron Configuration and Chemical Periodicity

actinides

The Period 7 elements that constitute the second inner transition series (5f block), which includes thorium (Th; Z = 90) through lawrencium (Lr; Z = 103).

amphoteric

Able to act as either an acid or a base.

atomic size

A measure of how closely one atom lies next to another, determined from the distances between nuclei of adjacent atoms.

aufbau principle

The conceptual approach for building up atoms by adding one proton at a time to the nucleus and one electron to the lowest energy sublevel that is available, to obtain the ground-state electron configurations of the elements

covalent radius

One-half the shortest distance between nuclei of identical covalently bonded atoms.

diamagnetic

A species that is not attracted by a magnetic field because its electrons are paired.

effective nuclear charge (Zeff)

The nuclear charge an electron actually experiences as a result of shielding effects due to the presence of other electrons.

electron affinity (EA)

The energy change (in kJ) accompanying the addition of 1 mol of electrons to 1 mol of gaseous atoms or ions.

electron configuration

The distribution of electrons within the levels and sublevels of the atoms of an element; also the notation for such a distribution.

Hund's rule

A principle stating that, when orbitals of equal energy are available, the electron configuration of lowest energy has the maximum number of unpaired electrons with parallel spins.

inner (core) electrons

Electrons that fill all the energy levels of an atom except the valence level; electrons also present in atoms of the previous noble gas and any completed transition series.

inner transition elements

The elements of the periodic table in which the seven inner f orbitals are being filled; the lanthanides and the actinides.

ionic radius

The size of an ion as measured by the distance between the nuclei of adjacent ions in a crystalline ionic compound.

ionization energy (IE)

The energy (in kJ) required for complete removal of 1 mol of electrons from 1 mol of gaseous atoms or ions

isoelectronic

Having the same number and configuration of electrons as another species.

Lanthanides

The Period 6 (4f) series of inner transition elements, which includes cerium (Ce; Z = 58) through lutetium (Lu; Z = 71).

metallic radius

One-half the shortest distance between the nuclei of adjacent individual atoms in a crystal of an element.

orbital diagram

A depiction of orbital occupancy in terms of electron number and spin shown by means of arrows in a series of small boxes or on a series of short lines

outer electrons

Electrons that occupy the highest energy level (highest n value) and are, on average, farthest from the nucleus

paramagnetic

A species with unpaired electrons that is attracted by an external magnetic field.

Pauli exclusion principle

A principle developed by Wolfgang Pauli stating that no two electrons in an atom can have the same set of four quantum numbers. The principle arises from the fact that an orbital has a maximum occupancy of two electrons and their spins are paired.

penetration

The phenomenon in which an outer electron moves through the region occupied by the core electrons to spend part of its time closer to the nucleus; penetration increases the average effective nuclear charge for that electron.

periodic law

A law stating that, when the elements are arranged by atomic mass, they exhibit a periodic recurrence of properties.

shielding

The ability of other electrons, especially those occupying inner orbitals, to lessen the nuclear attraction for an outer electron.

transition element

An element that occupies the d block or the f block (inner transition element) of the periodic table

valence electrons

The electrons involved in compound formation; in main-group elements, the electrons in the valence (outer) level.