Chemical bonding

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).

The Electron Structure of the Atom The quantum model emphasizes the wave nature of electrons. The Quantum Model Quantum numbers are solutions to the wave equations of electrons. Scientists use a set of 4 quantum numbers to determine an electron?s location around an atom. Quantum Numbers Electrons exist in principal energy levels that correspond to Bohr?s orbits: 1, 2, 3, 4, 5, ? Principal energy levels are divided into 4 types of sublevels: s, p, d, and f. Where are the Electrons? The sublevels contain orbitals. Each orbital can hold up to two electrons. Where are the Electrons? Identifies the principal energy level Correlates to Bohr?s orbits n = 1, 2, 3, 4, 5, 6, or 7 for the ground state e?. The total number of e? in a level is 2n2. Principal Quantum Number (n) Level Total # e? 1