Chapter 19 Chemical Bonding

What is the statue of liberty made out of? Copper Then why is it green and not the color of a penny? The outer layer of the copper has undergone a chemical change. The green color is copper sulfate (CuSO4) Copper sulfate contains copper sufur and oxygen. But carries with it none of the properties of any of those elemnets.

New Properties When elements chemically combine to form compounds most of the time the new substance has very different properties than any of the substances that make it up. Water Salt

Formulas Chemical formula- tells what elements a compound contains and the number of atoms of each element in a unit of that compound. H2O NaCl C6H12O6 SiO2 N2O

Atomic stability Atoms form compounds in order to form a more stable substance. Atoms are all looking for 8 valence electrons. When an atoms gets 8 valence electrons it is stable and happy.

Noble Gasses Group 18 on periodic table. Helium has two valence electrons. All others have 8 VEs NGs are chemically stable and do not react with anything in nature.

Outer levels Hydrogen and helium are happy with 2 valence electrons….. Why? Because they only have one energy level and the first EL only holds up to 2 electrons. All other elements are looking for 8 valence electrons

Stability is reached Stability is reached when the outer energy level is full for all atoms in the compound.

Section 2 Types of bonds

Ionic Bonds Ion- An atom that carries a charge due to gaining or losing electrons. Ionic Bond- the force of attraction between the opposite charges of the ions in an ionic compound. The result of ionic compounds should be a net charge of zero.

Covalent Bonds Covalent Bonds- the attraction that forms between atoms when they share electrons. Molecule-a neutral particle that forms as a result of electron sharing Single covalent bonds- bond that result from the sharing of ONE pair of electrons. (2 electrons) Double covalent bonds- bond that result from the sharing of TWO pairs of electrons (4 electrons) Triple Covalent bonds- sharing 3 pairs of electrons (6 electrons)

Unequal Sharing Electrons are not always shared equally in molecules. Some atoms “hog” the electrons This make them POLAR Polar Molecule- one that has a slightly positive end and a slightly negative end, due to unequal sharing of electrons. Nonpolar Molecule- molecule in which electrons are shared equally between atoms.

Section Three Writing and naming compounds

Binary Ionic Compounds Binary Ionic Compound- an ionic compound that is composed of two elements. In order to name binary ionic compounds you need to have certain pieces of inormation.

Info to name compounds Which elements are involved How many electrons they lose, gain, or share to become stable. Oxidation Number- tells you how many valence electrons an element gains, loses or shares to become stable. If an atom LOSES electrons, it has a POSITIVE oxidation number (Na) If an atom GAINS electrons, it has a NEGATIVE oxidation number (Cl)

Compounds are neutral When writing formulas you MUST have neutral compounds. If you have a +2 you must either find a -2 to bond with or two -1’s to bond with. You want to find the least common denominator in order to keep formula writing simple and neutral.

Rules for formula Writing Write the positive ion first. (single ion or polyatomic ion) Write the negative ion second. (single or polyatomic) Use subscripts for each ion so that the sum of the charges (oxidation #’s) is zero. (crisscross method)

Writing Names (ionic) Write the name of the positive ion first Write the name of the negative ion second and substitute the last part of the name with ide (chlorine becomes chloride; oxygen becomes oxide) If the positive ion can have more than one oxidation number, then determine the charge by looking at the formula and then write the charge of the ion using roman numerals to the left of the positive ion. (Fe2O3 becomes Iron (III) Oxide)

Naming Compounds (covalent) Write the most positive atom first. If there is only one then just write the name. If there are two or more use the proper prefix. Write the name of the most negative atom second ALWAYS using a prefix and substituting the last part of the name with ide