Bonding

The attraction between the positive nucleus of one atom and the negative electrons of another atom is what creates a chemical bond. A valence electron is an outermost electron of an atom that participates in chemical bonding.valence electron The number of valence electrons in each atom of an element can help determine the type and number of bonds that an atom can form. Atoms Bond

The periodic table can tell you how many valence electrons an atom has.

Atoms with eight valence electrons are chemically stable and do not easily react with other atoms. The elements in group 18 are called noble gases. With the exception of helium, noble gases have eight valence electrons and are chemically stable. Atoms that have between one and seven valence electrons are reactive or chemically unstable and easily bond with other atoms to form chemically stable compounds. Atoms Bond (cont.)

Atoms gain, lose, or share valence electrons and become chemically stable.

When unstable, nonmetal atoms bond together, they bond by sharing valence electrons. A covalent bond is a chemical bond formed when two atoms share one or more pairs of valence electrons.covalent bond A compound formed from many covalent bonds is called a covalent compound. Covalent Bonds—Electron Sharing

The chemically stable unit of a covalent compound is a molecule. A molecule is a group of atoms held together by covalent bonding that acts as an independent unit.molecule Covalent Compounds (cont.)

In a covalent bond, one atom can attract the shared electrons more strongly than the other atom can. A molecule that has a partial positive end and a partial negative end because of unequal sharing of electrons is a polar molecule.polar molecule Covalent Compounds (cont.)

When a metal and a nonmetal bond, they do not share electrons, they transfer electrons from the metal to the nonmetal. After the electrons transfer, the atoms bond and form a chemically stable compound. Transferring valence electrons results in atoms with the same number of valence electrons as a noble gas. Understanding Ions

Because electrons have a negative charge, losing or gaining an electron changes the overall charge of an atom. Atoms that lose valence electrons become ions with a positive charge. Atoms that gain valence electrons become ions with a negative charge. Understanding Ions (cont.)

Metal atoms, such as sodium, become more stable when they lose valence electrons and form a chemical bond with a nonmetal. Understanding Ions (cont.)

When forming a compound, the nonmetal atoms gain the electrons lost by the metal atoms. So metals become positively charged ions and nonmetals become negatively charged ions. The attraction between positively and negatively charged ions in an ionic compound is an ionic bond.ionic bond Ionic Bonds—Electron Transferring

Individual ions in an ionic compound are strongly attracted to each other. When nonmetal ions bond to metal ions in an ionic compound there is a large collection of oppositely charged ions and no molecules. Ionic Compounds

A metallic bond is a bond formed when many metal atoms share their pooled valence electrons.metallic bond Metal atoms form compounds by combining, or pooling their valence electrons. Valence electrons in metals are not bonded to one atom. Instead, a “sea of electrons” surrounds the positive ions. Metallic Bonds—Electron Pooling

Valence electrons are free to move among all the aluminum (Al) ions.