Chemical Bonds

Compound: a substance made from chemical bonding atoms of two or more elements. Chemical bond: a force that holds together the atoms in a substance. Remember: Atoms form compounds to become chemically stable. An atom is chemically stable when the outer level is complete or full (8 valence electrons.)

Chemical Formula: tells what elements a compound contains and the number of those atoms. How to Count Atoms: Coefficient: the number of molecules Superscript: represents the oxidation number of how many electrons lost or gained. 2 H2O SO42- Subscript: the # of atoms of an element in each molecule

Two Types of Chemical Bonds: Ionic Bonds transferring electrons between atoms of a metal and nonmetal Covalent Bonds sharing electrons between atoms of a nonmetal and nonmetal

Ionic Bond Definition of Ionic Bond: The attraction between 2 oppositely charged ions (+ and -) Ion: an atom or group of atoms that have become electrically charged. Positive Ion: when an atoms loses an electrons it loses a negative charge. protons > electrons Negative Ion: when atom gains an electron it gains a negative charge electrons > protons

11 Protons 12 Neutrons 10 Electrons 11 Protons 12 Neutrons 11 Electrons

Note: Atoms that have fewer than 4 Valence electrons, want to get rid of them…transfer electrons to other atoms. Atoms that have more than 4 Valence electrons, want to gain more electrons.

Example of Forming an Ionic Bond: Na = 1 valence electron Cl = 7 valence electrons Na (sodium) gives Cl (chlorine) one electron Na now has more protons than electrons → becomes a positive ion. Cl now has more electrons than protons → becomes a negative ion. Negative and positive electric charges attract each other Na 1+ + Cl 1- → Na+Cl-

Oxidation Number: the overall charge on the atom after losing or gaining an electron(s) Group # Elements Oxidation # Group 1 Li, Na, K 1+ Group 2 Mg, Be, Ca 2+ Group 16 O, S 2- Group 17 F, Cl,Br, I 1-

Naming Ionic Compounds The name of the positive ion comes first. The name of the negative ion comes next If the negative ion is an element, the end of its name changed to –ide. Example: MgO = Magnesium oxide.

Properties of Ionic Compounds Crystal shape High Melting Points Electrical Conductivity When ionic compounds dissolve in water, the solution can conduct electricity. Example: salt in water. Solid ionic compounds do not conduct electricity well