Chemistry

Chemical Composition &Reactions Oxidation Numbers Keep track of electrons during bonding Tell how many electrons are involved in the bond Tell whether electrons are gained, lost, or unequally shared Oxidation Numbers Help in predicting formulas The more electronegative element gains electrons. The oxidation number of atoms and elements is zero. (free-element) Rule 1 Oxidation Numbers Examples: He ? no bonds O2 ? equal sharing (free-element) Rule 1 Oxidation Numbers The oxidation number of a monatomic ion is equal to the charge of the ion. (ions) Rule 2 Oxidation Numbers Example: Mg loses two electrons, so its charge is +2; therefore, its oxidation number is also +2. (ions) Rule 2 Oxidation Numbers Example: Cl gains one electron, so its charge and oxidation number are ?1. (ions)

Bond Theories 1 Lewis Structures Tell us about bonds in a molecule Do not tell us about the shape of the molecule Valence Bond Theory Based on the quantum model Says that covalent bonds form when orbitals of different atoms overlap sigma (?) ? the ends of the orbitals overlap pi (?) ? the sides of the orbitals overlap Types When Orbitals Overlap Bonds: sigma bond Single Bond s sublevel 5 Chemistry textbook, p. 162 sigma bond Single Bond p sublevel 6 Chemistry textbook, p. 162 Which type of bond forms first between covalently bonded atoms? Sigma Pi Depends on the atom Question 7 sigma and pi bond Double Bond 8 Chemistry textbook, p. 162 sigma and 2 pi bonds Triple Bond 9 Chemistry textbook, p. 162 pi bond forms only after a sigma bond weaker than a sigma bond double bond

Section 6B Types of Bonds 1 Covalent Bonds usually nonmetals little or no ?EN (Therefore, atoms share electrons.) The 2 shared electrons are called a bonding pair. located between atoms most of the time Covalent Bonds The negative region between the atoms attracts the nuclei with an electrostatic force. Diatomic Elements H2 N2 O2 F2 Cl2 Br2 I2 ? triple bond ? double bond H N O Halogens Lewis Structures sometimes called dot diagrams show the valence e? only use a dash to represent a bonding pair Lewis Structures Cl2 + Cl Cl Cl Cl + Cl Cl Cl Cl Lewis Structures H2 + H H H H + H H H H Lewis Structures H2O + H O H + H O H + H O H + H O H Lewis Structures O2 O + O O O O + O O O Lewis Structures N2 N + N N N N + N N N Lewis Structures C2H2 + C C H + H + C C H H + C C H + H + C C H H

Elemental & Families Properties Their 1 Hydrogen: A Family of Its Own Why is it by itself? Can lose or gain one electron Discovered by Cavendish Physical properties (PP) Chemical properties (CP) Uses Hydrogen: A Family of Its Own Physical properties (PP) colorless, odorless, tasteless gas Chemical properties (CP) active, like a Group 1A metal or a Group 7A nonmetal diatomic can react with metals to form metallic hydrides Hydrogen: A Family of Its Own Uses ammonia fuel cells ?rocket? fuel Hydrogen: A Family of Its Own Supposed to have initially formed H & He Big Bang 6 Group 1: The Alkali Metal Family Physical properties light, soft, shiny, conduct electricity well 7 Chemical properties most reactive metals eager to lose lone outer e? never occur naturally

Periodic The Table 1 Lavoisier Made the first list of 30 substances he thought were elements D?bereiner Created a list of elements based on triads triads: groups of 3 elements with similar properties Created a list of elements based on triads problem with triads: Soon more elements were found; there were more than 3 similar elements to a group. D?bereiner periodicity repetition of a property on a regular basis Newlands Arranged elements by atomic mass Observed the ?law of octaves? Every 8th element repeats properties. Included the transition metals Mendeleev Developed the periodic table by arranging elements by atomic mass (like Newlands) Included the transition metals (like Newlands) Mendeleev Left blanks when properties or mass did not fit