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Chapter 1

Chemical Foundations

Shaun Williams, PhD

Chemistry: An Overview

Why chemistry seems hard

Atoms vs. Molecules

A single red sphere representing an oxygen atom. A single white sphere representing a hydrogen atom. Two white spheres connected to a red sphere representing a water molecule

Oxygen and Hydrogen Molecules

Two oxygen atoms connected is the oxygen molecule, written O2. Two hydrogen atoms connected is the hydrogen molecule, written H2.

A Chemical Reaction

Two water molecules can be split into one oxygen molecule and two hydrogen molecules by the application of an electric current.

The Scientific Method

Science

Fundamental Steps of the Scientific Method

  • Process that lies at the center of scientific inquiry.
A graphical representation of the scientific method.

Scientific Models

Units of Measurement

Nature of Measurement

Measurement

The Fundamental SI Units

Physical Quantity Name of Unit Abbreviation
Mass kilogram kg
Length meter m
Time second s
Temperature kelvin K
Electric current ampere A
Amount of substance mole mol
Luminous intensity candela cd

Prefixes Used in the SI System

Prefix Symbol Meaning Exponential Notation
exa \(\chem{E}\) \(1,000,000,000,000,000,000\) \(10^{18}\)
peta \(\chem{P}\) \(1,000,000,000,000,000\) \(10^{15}\)
tera \(\chem{T}\) \(1,000,000,000,000\) \(10^{12}\)
giga \(\chem{G}\) \(1,000,000,000\) \(10^{9}\)
mega \(\chem{M}\) \(1,000,000\) \(10^{6}\)
kilo \(\chem{k}\) \(1,000\) \(10^3\)
hecto \(\chem{h}\) \(100\) \(10^2\)
deka \(\chem{da}\) \(10\) \(10^1\)
- \(-\) \(1\) \(10^0\)

More Prefixes Used in the SI System

Prefix Symbol Meaning Exponential Notation
deci \(\chem{d}\) \(0.1\) \(10^{-1}\)
centi \(\chem{c}\) \(0.01\) \(10^{-2}\)
milli \(\chem{m}\) \(0.001\) \(10^{-3}\)
micro \(\chem{\mu}\) \(0.000001\) \(10^{-6}\)
nano \(\chem{n}\) \(0.000000001\) \(10^{-9}\)
pico \(\chem{p}\) \(0.000000000001\) \(10^{-12}\)
femto \(\chem{f}\) \(0.00000000000001\) \(10^{-15}\)
atto \(\chem{a}\) \(0.000000000000000001\) \(10^{-18}\)

Mass \(\ne\) Weight

Uncertainty in Measurement

Uncertainty in measurements

Measurement of Volume Using a Buret

  • The volume is read at the bottom of the liquid curve (meniscus).
  • Meniscus of the liquid occurs at about 20.15 mL.
    • Certain digits: 20.15
    • Uncertain digit: 20.15
A graphical representation of water in a buret.

Precision and Accuracy

Precision and Accuracy: Graphically

If all the darts on a dart board and randomly scattered you have an example of poor precision and poor accuracy. If all the darts miss the center but are all clustered together you have good precion but poor accuracy. If all the darts are clustered in the center you have good precision and good accuracy.

Significant Figures and Calculations

Rules for Counting Significant Figures

  1. Underline the left-most, nonzero digit.
    • \(\underline{2}73.1023\)
    • \(0.\underline{1}023\)
    • \(0.\underline{7}10\)
    • \(\underline{1}0.025\)
    • \(\underline{1}020\)

Rules for Counting Significant Figures (cont.)

  1. We look to a decimal point.
    1. If the number contains a decimal point, underline the right-most digit.
      • \(\underline{2}73.102\underline{3}\)
      • \(0.\underline{1}02\underline{3}\)
      • \(0.\underline{7}1\underline{0}\)
      • \(\underline{1}0.02\underline{5}\)
    2. If the number does not contain a decimal point, underline the right-most, nonzero digit.
      • \(\underline{1}0\underline{2}0\)

Rules for Counting Significant Figures (concluded)

  1. Count the numbers from one underlined number to the other.
    • \(\underline{2}73.102\underline{3}\) has 7 sig. figs.
    • \(0.\underline{1}02\underline{3}\) has 4 sig. figs.
    • \(0.\underline{7}1\underline{0}\) has 3 sig. figs.
    • \(\underline{1}0.02\underline{5}\) has 5 sig. figs.
    • \(\underline{1}0\underline{2}0\) has 3 sig. figs.

Special Types of Numbers

Exponential Notation

Significant Figures in Mathematical Operations

  1. For multiplication or division, the number of significant figures in the result is the same as the number in the least precise measurement used in the calculation. $$ 1.342 \times \underline{5.5} = 7.381 \xrightarrow{\chem{round}} \underline{7.4} $$
  2. For addition or subtraction, the result has the same number of decimal places as the least precise measurement used in the calculation. $$ 23.445 + 7.8\underline{3} = 31.275 \xrightarrow{\chem{round}} 31.2\underline{8} $$

Concept Check!

You have water in each graduated cylinder shown. You then add both samples to a beaker (assume that all of the liquid is transferred).

How would you write the number describing the total volume?

What limits the precision of the total volume?

Two different sized graduated cylinders, the first containing 2.8 mL and the second containing 0.28 mL.

Concept Check! Answer

You have water in each graduated cylinder shown. You then add both samples to a beaker (assume that all of the liquid is transferred).

How would you write the number describing the total volume? \(3.1\,\chem{mL}\)

What limits the precision of the total volume? The precision of the left graduated cylinder is to the tenths place while the right graduated cylinder is to the hundreths place so the left graduated cylinder limits the precision of the sum.

Two different sized graduated cylinders, the first containing 2.8 mL and the second containing 0.28 mL.

Dimensional Analysis

Converting between unit systems

Example #1

A golfer putted a golf ball 6.8 ft across a green. How many inches does this represent?

Temperature

Three Systems for Measuring Temperature

Water freezes at 32 F, 0 C, and 273.15 K.

Density

Density

$$ \chem{Density}=\frac{\chem{mass}}{\chem{volume}} $$

Classification of Matter

Matter

In solid water, the molecules are well order,stuck in place, and close together. In liquid water, the molecules are randomly arranges, moving a little, and still close together. In gaseous water, the molecules are randomly arranged, moving very rapidly, and far apart. These conditions are true for all molecules in these phases.

The Phases - Macroscopically

Mixtures

Have variable composition.

Concept Check!

Which of the following is a homogeneous mixture?

Concept Check! Answer

Which of the following is a homogeneous mixture?

Physical Change

Chemical Change

Concept Check!

Which of the following are examples of a chemical change?

Concept Check! Answer

Which of the following are examples of a chemical change?

The Organization of Matter

Matter can be broken down into mixtures and pure substances. Mixtures can be broken down into heterogeneous and homogeneous mixtures. Pure substances can be broken down into elements and compounds. Elements are made up of atoms.

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