Tuesday, May 5, 2009

Electrons, Chemical Bonds and Periodic Table.

The chemical properties of an atom are determined largely by how full or empty the outer electron shell is. For example, atoms of fluorine(F), chlorine(Cl) and the other elements in that second from the last column of the periodic table need only one electron to fill the outer shell. These atoms have a very strong tendency to steal electrons from other atoms. Oxygen and sulphur have 6 electrons in their outer shell which again holds 8 maximum. Thus these elements tend to steal electrons.
Elements such as Lithium(Li) Sodium(Na) and Potassium(K) on the left hand side of the periodic table have an almost empty shell and these elements readily give up those outer shell electrons to atoms such as oxygen and chlorine. Elements that tend to give up electrons to other atoms are called metals.

Elements in the middle of the periodic table tend to share electrons rather than give them up or take them entirely. Many of these such as iron, copper or gold are also considered metals.

The elements at the far right: Helium, Neon, Argon etc... are chemically inert because they have a full outer shell. They will only react with other chemicals under very special conditions. These elements are sometimes called the 'noble' or inert gases because it is so difficult to get them to form chemical bonds.

Electronegativity: The tendency of atoms to grab electrons is called electronegativity. Here is a periodic table showing relative electronegativities. Higher electronegativites are shown in blue. Notice Fluorine(F) is the most electronegative element. Oxygen and chlorine less so.

Note that many of the elements we think of as metals iron(Fe), nickel(Ni), Copper(Cu), Silver(Ag) are intermediate in electronegativity between the metals in red on the far left of the table(low electronegativity) and the column near the right that contains fluorine(F). But real strong metals such as sodium or potassium ready give up electrons.

So the rule of thumb is atoms of the elements on the left side of the periodic table have a tendency to give up their electrons to atoms of the elements in the row beginning with chlorine. This is important because it dicatates the kinds of chemical bonds there elements will form with each other.

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