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Explore the formation of compounds through the combination of elements, including the formation of ionic, covalent, polyatomic, and metallic bonds. Discover the unique properties that result from these bonds and the role of atomic stability in compound formation.
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Chapter 5 • Combined elements • Compounds = unique properties from the elements that make them up. • NaCl for example • Na = shiny, soft, silvery, metal that reacts violently with water • Cl = a poisonous greenish yellow gas • NaCl = table salt
Formulas • Chemical formula = tells what elements a compound contains and the exact number of atoms of each element in a unit of that compound. • Example: N2O = (2 nitrogen atoms 1 oxygen atom)
Atomic Stability • Why do atoms form compounds? • The electric forces between electrons and protons (opposites) cause compounds to form
Atomic Stability • An atom is chemically stable when its outermost energy level has the maximum number of electrons. • For H and He …2 electrons equal stable • For all other elements…8 electrons = stable
How do outer levels get their fill? • Atoms with partially stable outer energy levels can lose, gain, or share electrons to obtain stable outer energy levels • Ion = an charged particle because it has more or less electrons than protons • They do this by combining with other atoms
Chemical Bond • Chemical bond = the force that holds atoms together in a compound • The force occurs when atoms gain, lose, or share electrons…an attraction forms that pulls the atoms together to from a compound
What holds bonded atoms together? • When their valence electrons interact (outer most shell) • Atoms join so that each atom has a full outermost energy level
Ionic Bonds • Formed by the transfer of electrons • Ex) Na+ bonds w/ Cl- = NaCl • Each atom loses or gains electrons • Metals bond with nonmetals • Melting point = high • Ionic bonds tend to conduct electricity
Covalent Bonds • Bond formed when elements share one or more electrons. • Ex) Cl- bonds with a Cl- = Cl2 EX) C+2 bonds w/ O-2 = CO (carbon monoxide) • Nonmetals combine with nonmetals • Melting point = low
Polyatomic Ions • Can have both ionic and covalent bonds • Usually groups of covalently bonded atoms that have lost or gained electrons • Ex) NaHCO3 (sodium hydrogen carbonate) NaOH (Sodium Hydroxide) (NH4)SO4 (ammonium sulfate)
Metallic Bonds • Bond formed by the attraction between positively charged metal ions • Electrons move freely from metal atom to metal atom • This is why metals conduct electricity so well