Atomic Stability Atoms combine when the compound formed is more stable than the separate atoms Noble gases—seldom form compounds—Why?—They are unusually stable An atom is chemically stable when its outer energy level is complete (octet rule)

Outer Levels Atoms with partially stable outer energy levels can lose, gain, or share electrons to obtain a stable outer energy level. They do this by combining with other atoms that have partially complete outer energy levels to achieve stability Ex: pg. 577

Stability is Reached When atoms gain, lose, or share electrons, an attraction forms between atoms, pulling them together to form a compound Chemical bond—the force that holds atoms together in a compound

Section 2—Types of Bonds Ion—an atom that has lost or gained electrons – A charged particle because it now has either more or fewer electrons than protons – Positive and negative charges are not balanced – Ex: sodium chloride, sodium fluoride, potassium iodide

When an atom loses an electron, the atom becomes positively charged The 1+ charge is shown as a superscript written after the element’s symbol—pg. 581 When an atom gains an electron, the atom becomes negatively charged and is shown as a negative superscript

When one atom loses an electron and another atom gains that electron, the resulting compound of the two elements is NEUTRAL because the positive and negative charges of the ions cancel each other

Ionic bond-- formed by two ions of opposite charge either losing or gaining electrons to make a full outer valence In an ionic bond—a transfer of electrons takes place The result of an ionic bond is a neutral compound (sum of charges of ions is zero)

Sharing Electrons Covalent bond-- forms when two atoms share electrons to create a stable outer energy level Molecule—formed by covalent bonding (neutral particle) Single covalent bond—made up of two shared electrons (there are also double-4 shared electrons and triple— 6 shared electrons)

Bonding Facts: Ionic bonds—form between metals and nonmetals and are often crystalline solids Covalent bonds—form between nonmetallic elements Many covalent bonds are liquids or gases at room temperature