Section 3

Electron Configuration and Periodic Properties

Atomic Radii

Atomic Radius- defined as one-half the distance between the nuclei of identical atoms that are bonded together.
Periodic Trend- the trend to smaller atoms across a period is caused by the increasing positive charge of the nucleus.
Group Trend- In general the atomic radii of the main-group elements increase down a group.

Ionization Energy

Ion- atom or group of bonded atoms that has a positive or negative charge.
Ionization energy- the energy required to remove one electron from a neutral atom of an element
Period trend of ionization energies- ionization energies of the main-group elements increase across each period.
Group trend ionization energies- among the main-group elements, ionization energies generally decrease down the groups.
Removing Electrons from Positive Ions- each successive electron removed from an ion feels an increasingly stronger effective nuclear charge.
Electron Affinity- the energy change that occurs when an electron is acquired by a neutral atom

Ionic Radii

Cation- positive ion
Anion- negative ion

Valence Electrons

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


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

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