Chemical bond

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

Periodic Trends 1 Sizes of Atoms Increase from top to bottom on the periodic table Why? There are higher energy levels, and electrons are farther from the nucleus. Atomic Radii Sizes of Atoms Decrease from left to right on the periodic table Why? There are more protons in the nucleus attracting more electrons (electrostatic attraction). Atomic Radii Atomic Radii 4 p. 113 of Chemistry textbook (BJU Press) Question Why do atoms get larger as you go down the periodic table? They are heavier. They are less dense. Electrons are further from the nucleus. Electrons are bigger. 5 (Comparing the size of an atom to that of its ion, not going across or up the table) Sizes of Atoms Ionic Radii Sizes of Atoms Atoms that lose outer electrons have smaller positive ions (metals).