Electron Configuration

and Periodic Properties

Atomic Radii

An atomic radius can vary under different conditions. In order to compare atomic radii, you have to measure them under certain conditions. Atomic radius may be defined as one-half the distance between the nuclei of identical atoms that are bonded together. The trend to smaller atoms across a period is caused by the increasing positive charge of the nucleus. Atoms tend to be larger the farther down in a group they are found. As electrons is added to the s and p sublevels, they move closer to the nucleus. As a result, the difference in the radii between neighboring atoms in each period grows smaller. In general, the atomic radii of the main-group elements increase down a group.

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Ionization Energy

An electron being removed from an atom is shown by: A+energy-->A+ +e-. The A+ shows the element with a single positive charge. An ion is an atom or group of bonded atoms that has a positive or negative charge. Ionization is referred to any process that results in the formation of an ion. Ionization energy is used to compare how effortlessly atoms of different elements give up electrons. Ionization Energy (IE) is the energy required to remove one electron from a neutral atom of an element. Measurements of ionization energies are made by measuring isolated atoms in the gas phase. The more reactive an element is, the easier it loses electrons. The noble gases have low reactivities because of this. Ionization energies of transition metals increase across the periodic table. Increasing nuclear charge, increases ionization and decreases radii across the periods. Ionization energies of the main-group element increase across each period. This increase is caused by increasing nuclear charge. A higher charge more strongly attracts electrons in the same energy level. Ionization energies usually decrease down the groups. Electrons removed from atoms of each succeeding element in a group are in higher energy levels, farther from the nucleus.

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Electron Affinity

The energy change that occurs when an electron is acquired by a neutral atom is called the atom’s electron affinity. Electron affinity increase across periods and decreases down groups. The larger an atom's electron cloud is, the farther away its outer electrons are from its nucleus. The formula when atoms release energy and acquire energy, is A+e- -------> A-+energy. The formula when atoms are “forced” to gain an electron by the addition of energy, is A+e- +energy------> A-.

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Ionic Radii

A positive ion is called cation. The formation of a cation by the loss of one or more electrons leads to a decrease in atomic radius. The electron cloud becomes smaller. The remaining electrons are drawn closer to the nucleus by its unbalanced positive charge. A negative ion is called an anion. The formation of an anion by the addition of one or more electrons always leads to an increase in atomic radius. Cationic and anionic radii decrease across a period. THe electron cloud shrinks due to the increasing nuclear charge acting on the electrons in the same main energy level. The outer electrons in both cation and anions are in higher energy levels as one reads down a group. THere is a gradual increase of ionic radii down a group.

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Valence Electrons

Chemical compounds from because electrons are lost, gained, or shared between atoms. The electrons that interact in this manner are those in the highest energy levels. The electrons available to be lost, gained, or shared in the formation of chemical compounds are referred to as valence electrons. Valence electrons are often located in incompletely filled main-energy levels.

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Valence electrons hold atoms together in chemical compounds. In many compounds, the negative charge of the valence electrons is concentrated closer to one atom than another. Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound. Electronegativities tend to increase across periods, and decrease or remain about the same down a group.

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