Notes for CHEN 1211 - Chemistry for engineers, taken Fall 2016.

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Chapter 1 - Matter and Measurement

Significant Figures

These sigfigs are important.

The rules are as follows.

  1. Non-zero digits are always significant.
  2. Any zeros between non-zero digits are significant.
  3. Any trailing zeros in the decimal portion only are significant.

Unit Conversion

Unit conversion is simple. Just think through it ahead of time.

Chapter 2 - Atoms, Molecules, and Ions

Law of Mass Conservation

Mass is neither created nor destroyed in chemical reactions.

Law of Definite Proportions

Different samples of a pure chemical compound always contain the same proportion of elements by mass.

Law of Multiple Proportions

Elements can combine in different ways to form different chemical compounds, with mass ratios that are small whole-number multiples of each other.

Atomic Numbers

Elements differ from one another according to the number of protons in their atom's nuclei, called the atomic number.

The mass number on the other hand, is equal to the number of protons plus the number of neutrons.

Atoms with identical atomic numbers but different mass numbers are called isotopes.

Atomic Units

The atomic mass unit (amu) is defined as exactly $1/12$ the mass of an atom of ${}^{12}_6C$ and is equal to $1.660\,539 \times 10^{-24} g$

On the periodic table, an elements atomic mass is the weighted average of the isotopic masses of the elements naturally occuring isotopes.

Moles

One mole of any element is the amount whose mass in grams, called its molar mass, is numerically equal to its atomic mass. One mole of any element contains $6.022\,141 \times 10^{23}$ atoms, called Avogadro's Number.

Radioactivity

  1. $\alpha$ - two protons and two neutrons.
  2. $\beta$ - Proton and Electron
  3. $\gamma$ - Electromagnetic wave
  4. Positron emission when a proton in nucleus changes into neutron plus an ejected positron.
  5. Electron capture when the nucleus captures a nearby electron, converting a proton into a neutron.

Bonds

Covalent Bond

When two atoms share several (usually two) electrons. These are called molecules.

Ionic Bonds

Transfer of one or more electrons from one atom to another. This usually occurs between a metal and a non-metal.

When these happen, it's common for a cation (positive ion) or an anion (negative) ion to form.

Charged, covalently bonded groups of atoms, called polyatomic ions are also common.

Naming

Binary Ionic Compounds

Name the positive ion first by its full name, followed by the negative ion ending with "-ide". Charge is denoted with roman numerals. For instance,

  • $\text{Fe}^{2+} =$ Iron(II) ion
  • $\text{Fe}^{3+} =$ Iron(III) ion

Naming Binary Molecular Compounds

This uses the same strategy as ionic compounds. The more cationlike element takes the name of the element, and the more anionlike element uses an "-ide" ending. This is generally decided by saying that the more the to lower left the more cationlike, and the more to the upper right, the more anionlike.

Polyatomic Ions

Must be memorized...

Chapter 3 - Mass Relationships in Chemical Reactions

Balancing Chemical Equations

This is straigtforward. By editing coefficients make sure that matter is neither created nor destroyed.

Stoichiometry

To actually perform these chemical reactions you need to convert a number ratio of reactant molecules to a mass ratio.

The molecular mass of a substance is the average mass of the substance's molecules.

The formula mass is the sum of the atomic masses of all atoms in the molecule.

TL;DR Moles (number of molecules) are given by the coefficients in the balanced equation, but grams are used to weigh reactants in a lab. For the given equation $\alpha A + \beta B \to \gamma C + \delta D$, if we are given grams of $A$, we convert $A$ to moles, find the mole ratios in the equation, from which we now have the moles of $B$, which we can convert back to grams.

Yields of Reactions

Percent yield is defined as

$$ \text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100 $$

Concentrations of Reactants in Solution: Molarity

Molarity is defined as the number of moles of a substance disolved in enough solvent to make 1L of solution.

$$ \text{Molarity} = \frac{\text{Moles of Solute}}{\text{Liters of Solution}} $$

Diluting Concentrated Solutions

$$ M_f = M_i \cdot \frac{V_i}{V_f} $$

Percent Composition & Empirical Formulas

By examining chemical reactions in a lab, we can guess at the chemical equations behind the reactions.

Chapter 4 - Reactions in Aqueous Solutions

Chapter 5 - Periodicity and the Electronic Structure of Atoms

Appendix - Youtube Videos Linked on D2L

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