Atoms Ions and Chemical Bonds

I. Covalent bonds are formed by atoms that share electrons. They are the strongest type of chemical bond.

A. Electrons are equally shared in nonpolar covalent bonds and unequally shared in polar covalent bonds.

B. Atoms of oxygen, nitrogen, and phosphorus strongly attract electrons and become electrically negative compared to the other atoms sharing electrons with them.

II. Ionic bonds are formed by atoms that transfer electrons. These weak bonds join atoms together in an ionic compound.

A. If one atom in this compound takes an electron from another atom, it gains a net negative charge and the other atom becomes positively charged.

B. Ionic bonds easily break when the ionic compound is dissolved in water. Dissociation of the ionic compound yields charged atoms called ions.

III. When hydrogen bonds with an electronegative atom, it gains a slight positive charge and is weakly attracted to another electronegative atom. This weak attraction is a hydrogen bond.

IV. Acids donate hydrogen ions to solution, whereas bases lower the hydrogen ion concentration of a solution.

A. The pH scale is a negative function of the logarithm of the hydrogen ion concentration.

B. In a neutral solution, the concentration of H+ is equal to the concentration of OH-, and the pH is 7.

C. Acids raise the H+ concentration and thus lower the pH below 7; bases lower the H+ concentration and thus raise the pH above 7.

V. Organic molecules contain atoms of carbon and hydrogen joined together by covalent bonds. Atoms of nitrogen, oxygen, phosphorus, or sulfur may be present as specific functional groups in the organic molecule.

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