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Chemistry I (CHEM 105) Chemistry Final Exam Study Guide

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Washington State University

[P] Principles Of Chemistry I (CHEM 105)

Chemistry 101 Final Exam Study Guide- Spring 2017
Acids and Bases
Acid: substance that provides H+ ions in water
Base: substance that provides OH- ions in water
Covalent Bonds
 Review: ionic bonds are formed by the positive charge of the cation being attracted to the
negative charge of the anion
 Covalent bonds: bonds formed by sharing electrons between the atoms (not ions)
o 1 electron from each atom (2 atoms per bond)
o Electrons available for bonding are the un-paired electrons in orbitals (orbitals with only
1 electron in them)
 Molecule
o A group of atoms held together by covalent bonds
 Atoms will bond with enough other atoms to complete the octet
o But they can only form as many bonds as unpaired valence electrons
 Hydrogen has 1 valence electron, so it can only form 1 bond, and will not
achieve an octet
 Boron has 3 valence electrons, so can only form 3 bonds, and will not achieve
the octet (only 6 electrons)
o There are always exceptions to the rules
 Sulfur and phosphorus can extend the octet
Multiple Covalent Bonds between 2 atoms
 If the octet is not met, additional bonds may be formed
o Co2 (carbon dioxide)
 C has 4 valence electrons, so 4 bonds possible
 O has 6 valence electrons, 2 are unpaired, so 2 bonds are possible
PRACTICE
IONS:
 Sodium
o Symbol: Na
o Valence: 1
o Electron dot: Na*
o Ionic dot: Na+ (loses its electron to get a 1+ charge)
 Magnesium
o Symbol: Mg
o 2 valence Eo
Loses 2 electrons to get 2+ charge
 Oxygen
o Symbol: O
o Valence: 6
o Will gain 2 electrons for a 2- charge
Cannot have a covalent bond with ions, just atoms
January 30th, 2017 Lecture
Expanding Condensed Structures
 Connectivity is from left to right
Drawing Lewis Structures
1. Determine the total number of valence electrons in the molecule or ion
2. Draw a line between each pair of atoms connected. Each line represents 2 electrons.
3. Use the remaining electrons on the outer atoms to satisfy the octet rule
4. Place any remaining electrons in lone pairs around the central atom
5. If the central atom does not satisfy the octet, use lone electrons from the outer atoms to form
additional bonds between the center and outer atoms.
Resonance Structures
 If more than one valid Lewis structure can be drawn for a molecule or ion, then the molecule or
ion has resonance, and each of the possible Lewis structures are resonance structures of each
other
 Resonance structures are identified by a double-ended arrow pointing between each structure
Number of resonance structures
 Look at the number of equivalent atoms surrounding the center atom
o If the bonds between each of the equivalent atoms and the center atom are the same,
there are no resonance structures
o If the bonds between each of the equivalent atoms and the center atom are NOT the
same, there ARE resonance structures
 The number of resonance structures is determined by how many spots on the
molecule you can move the different bonds to
February 1st, 2017
Wednesday, February 1, 2017
12:24 PM
VSEPR (Valence Shell Electron Pair Repulsion)
 Model used to predict the molecular shapes and geometries of molecules
 Identifies the atoms and lone pairs of electrons connected to an atom of interest as an “electron
charge cloud”
 AXE designation:
o AXaEb
 Where a=number of atoms connected to atom of interest
 Where b= number of lone pairs of electrons on the atom of interest
 A= center atom
 X= other atoms attached to center atom
 E= lone pairs of electrons
Geometries of molecules
1. Draw the most stable Lewis structure for the molecule
2. Count the number of electron charge clouds around the atom of interest. An electron charge
cloud can be 1 lone pair of electrons or 1 connected atom
3. The geometry corresponds to the number of electron charge clouds around the atom of interest
a. 2 electron charge clouds= linear

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Chemistry I (CHEM 105) Chemistry Final Exam Study Guide

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