High School Chemistry Notes

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03.04 Valence Electrons and Bonding

Individual neutral atoms are rarely found in nature. The noble gases are the only elements that are found as single atoms more often than they are found in compounds. Atoms are held together in compounds by electrostatic attraction between positive nuclei and negative electrons. This attraction holds atoms together in a chemical bond, a link between two atoms resulting from the mutual attraction of their nuclei for valence electrons. All chemical bonds involve valence electrons, but the bonds are classified by the way in which electrons are distributed within the bonds.

Ionic and Covalent Bonds
We will be studying two types of chemical bonds in this module: ionic bonds and covalent bonds. Atoms can gain or lose electrons to become charged ions. Metals tend to lose electrons and nonmetals tend to gain electrons to give them a full valence like a noble gas. Positive ions and negative ions are attracted to each other because of their opposite charges. They form ionic bonds, a chemical bond that results from electrostatic attraction between positive and negative ions. This means that in an ionic bond, electrons are given up by one atom and gained by another atom, and then those atoms are attracted to each other. In another type of chemical bond, called a covalent bond, electrons are shared between two atoms, neither atom completely gains or loses electrons. Because the two atoms, often both nonmetals, overlap their valence energy levels, both atoms “own” those shared electrons.

Electronegativity and Bond Properties
Chemical bonds can range in strength and properties between completely ionic and completely covalent, depending on how strongly the atoms attract the electrons. Comparing their electronegativity values helps chemists estimate the degree of ionic or covalent properties of various chemical bonds. The greater the difference in their electronegativity values, the more ionic the chemical bond between two atoms....
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