The Periodic Law

Electron Configuration and Periodic Properties

Electron Configuration and Periodic Properties

Atomic Radii

*Atomic radius- may be defined as one-half the distance between the nuclei of identical atoms that are bonded together.

Period Trends

*The trend to smaller atoms across a period is caused by the increasing positive charge of the nucleus.

Group Trends

*In general, the atomic radii of the main-group elements increase down a group.

Ionization Energy

*A + energy ---> A+ + e´

*Ion- is an atom or group of bonded atoms that has a positive or negative charge.

*Ionization- any process that result in the formation of an ion.

*Ionization energy (IE)- the energy required to remove one electron from a neutral atom of an element.

Period Trends

*In general, ionization energies of the main-group elements increase across each period.

Group Trends

*Among the main-group elements, ionization energies generally decrease down the groups.

Removing Electrons from Positive Ions

*The second ionization energy (1E2), third ionization energy (1E3), and so on.

*Thus, each successive electron removed from an ion feels an increasingly stronger effective nuclear charge (the nuclear charge minus the electron shielding).

Electron Affinity

*Electron affinity- the energy change that occurs when an electron is acquired by a neutral atom.

*A + e´------> A´ + energy

*A + e´+ energy --------> A´

Period Trends

*Among the elements of each period, the halogens gain electrons most readily. As electrons add to the same p sublevel of atoms with increasing nuclear charge, electron affinities become more negative across each period within the p block.

Group Trends

*Trends for electron affinities within groups are not as regular trends for ionization energies. Electrons add with greater difficulty down a group. The first is a slight increases electron affinities. The second is an increase in atomic radius down a group, which decreases electron affinities.

Adding Electrons to Negative Ions

*For an isolated ion in the gas phase, it is always more difficult to add a second electron to an already negatively charged ion. All second electrons are all positive. Certain p-block nonmetals tend to form negative ions that have noble gas configurations.

Ionic Radii

*Cation- a positive ion,

*Anion- a negative ion.

Period Trends

*Within each period of the periodic table, the metals at the left tend to form cations and the nonmetals at the upper right tend to form anions. Cationic radii decrease across a period because the electron cloud shrinks due to the increasing nuclear charge acting on the electrons in the same main energy level.

Group Trends

*As they are in atoms, the outer electrons in both cations and anions are in higher energy levels as one reads down a group.

Valence Electrons

*Valence Electrons- the electrons available to be lost, gained, or shared in the formation of chemical compounds.


*Electronegativity- a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound.

Period Trend

*Electronegativities tend to increase across each period, although there are exceptions.

*Electronegativities tend to either decrease down a group or remain about the same.

Periodic Properties of the d- and f-Block Elements

*The properties of the d-block elements vary less and with less regularity than those of the main-group elements.

Atomic Radii

*The atomic radii of the d-block elements generally decrease across the periods. As the number of electrons in the d sublevel increases, the radii increase because of repulsion among the electrons.

Ionization Energy

*As they do for the main-group elements, ionization energies of the d-block and f-block elements generally increase across the periods.

Ion Formation and Ionic Radii

*Among all the atoms of the d-block and f-block elements, electrons in the highest occupied sublevel are always are always removed first.


The d-block element all have electronegativities between 1.1 and 2.54.

By Kelly Kuboushek and Monica Schwartzhoff

All information came from the book.

All images came from google images.