Class notes
CHM 113 - General Chemistry I Exam 2 Notes
- Course
- CHM 113 (CHM113)
- Institution
- Arizona State University
This is a note sheet for Exam 2 of General Chemistry I offered at ASU. It contains lecture material and examples.
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Chapter 2.6 - 2.8Chemical Formula - The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.
Molecular Compounds - They are composed of molecules and almost always contain only non-metals.
The 7 Diatomic Molecules - “Have No Fear of Iced Cold Beer”
• Hydrogen (H2)
• Nitrogen (N2)
• Oxygen (O2)
• Fluorine (F2)
• Chlorine (Cl2)
• Bromine (Br2)
• Iodine (I2)
When an atom of a group of atoms loses or gains electrons, it becomes an ion.
Ion Notations
• Charges are shown as superscripts after symbol.
• + and - are used to show positive and negative charges.
• For +1 and -1, the one is generally implied.
• Any element written without charge is neutral.
Cations - Form when at least one electron is lost. Monatomic cations are formed by metals. They are usually written first in a chemical formula. Use the elemental name.
Anions - Form when at least one electron is gained. Monatomic anions are formed by nonmetals, except the noble gases. They are usually written second in a chemical formula.
Use the elemental name with -ide suffix.
Oxidation Number - A number assigned to each atom in a compound to represent the “charge” each would have if the electrons were divided among the atoms.
Rules for Assigning Oxidation Numbers (ONs):
1. Pure elements (including those that exist as diatomics) are assigned a zero for their ON.
N2 (g)
N - 0, N - 0
2. Monatomic ions have an ON equal to their common charge.
• Metals always have a positive charge.
• Group 1A metals have an ON = +1.
• Group 2A metals have an ON = +2.
• Other metals often have a charge equal to their group number on the Periodic Table. (Does not apply to transition metals that have more than one
oxidation number).
3. The ON of a non-metal depends on what other elements it is bonded to, but can be assigned in the following order:
• Fluorine (F) has an ON of -1, ALWAYS.
• Hydrogen (H) has an ON of +1 (Has an ON of -1 when bound to a metal).
• Oxygen has an ON of -2 (Has an ON of +2 when bound to F and has an ON of -1 when in peroxide, and a -1/2 in superoxides).
• Halogens (Group 7A) have an ON of -1.
4. The sum of all the ONs in a compound/ion must add up to the overall charge of the compound/ion. For neutral compounds, this charge is zero.
Halogen Oxyanions
- The ion with two oxygens ends in -ite.
- The ion with three oxygens ends in -ate.
- The ion with one oxygen has the prefix hypo- and ends in -ite.
- The ion with four oxygens has the prefix per- and ends in -ate.
Ionic Compounds (such as NaCl) are generally formed between metals and nonmetals, or metals and negatively charge polyatomic ions. Electrons are transferred from the metal
to the nonmetal. The oppositely charged ions attract each other to form ionic bonds. Only empirical formulas are written.
Binary Ionic Compounds:
- Write the symbols for cation and anion with the correct charges.
- Put the ions together and balance the charges (Cations are always written first).
Polyatomic Ionic Compounds:
- Treat each polyatomic ion as ONE ion.
Acids (Strong) Acids (Weak) Bases (Strong) Bases (Weak)
HCI - hydrochloric acid CH3COOH - acetic acid NaOH - sodium hydroxide NH3 - ammonia
HBr - hydrobromic acid H3PO4 - phosphoric acid LiOH - lithium hydroxide C5H5N - pyridine
HI - hydroiodic acid H2S - hydrosulfuric acid KOH - potassium hydroxide CH3NH2 - methylamine
HNO3 - nitric acid HCN - hydrocyanic acid RbOH - rubidium hydroxide
H2SO4 - sulfuric acid HCOOH - formic acid CsOH - cesium hydroxide
HCIO4 - perchloric acid HF - hydrofluoric acid Ca(OH)2 - calcium hydroxide
HCIO3 - chloric acid HNO2 - nitrous acid Ba(OH)2 - barium hydroxide
Chapter 3.1-3.7
Guidelines for Balancing Equations
1. Write correct formulas for reactants and products.
2. Balance atoms of each element using coefficients, not subscripts.
3. Start by focusing on the element that appears in the fewest compounds OR start with the most complex formula compounds.
4. Balance polyatomic ions as a single unit with coefficients if the polyatomic ion(s) exist on both sides of the equation.
Formula Weight (FW) is the sum of the atomic weights for all the atoms in a chemical formula for an ionic compound.
Example: NaCl
Na: 1 (22.99 amu) + Cl: 1 (35.45 amu) = 58.44 amu
Molecular Weight (MW) is the sum of the atomic weights for all the atoms in a chemical formula for a molecular compound.
Example: C2H5OH
C: 2 x (12.011 amu) + H: 6 x (1.008 amu) + O: 1 x (16.00 amu) = 46.07 amu
Percentage Composition from Chemical Formulas
% Element = (number of atoms)x(atomic weight) / FW or MW of the compound) x 100
1 amu = 1.66054 x 10-24 g
23
6.02214 x 10 amu = 1 gram
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