
# Chapter 1 Chemical Foundations

Shaun Williams, PhD

## Chemistry: An Overview

### Why chemistry seems hard

• A main challenge of chemistry is to understand the connection between the macroscopic world that we experience and the microscopic world of atoms and molecules.
• You must learn to think on the atomic level.

### Atoms vs. Molecules

• Matter is composed of tiny particles called atoms.
• Atom: smallest part of an element that is still that element.
• Molecule: Two or more atoms joined and acting as a unit.

### Oxygen and Hydrogen Molecules

• Use subscripts when more than one atom is in the molecule.

### A Chemical Reaction

• One substance changes to another by reorganizing the way the atoms are attached to each other.

## The Scientific Method

### Science

• Science is a framework for gaining and organizing knowledge.
• Science is a plan of action — a procedure for processing and understanding certain types of information.
• Scientists are always challenging our current beliefs about science, asking questions, and experimenting to gain new knowledge.
• Scientific method is needed.

### Fundamental Steps of the Scientific Method

• Process that lies at the center of scientific inquiry.

### Scientific Models

• Law - A summary of repeatable observed (measurable) behavior.
• Hypothesis - A possible explanation for an observation.
• Theory (Model) - Set of tested hypotheses that gives an overall explanation of some natural phenomenon.

## Units of Measurement

### Nature of Measurement

Measurement

• Quantitative observation consisting of two parts.
• number
• scale (unit)
• Examples
• $$20\, \chem{grams}$$
• $$6.63 \times 10^{-34}\,\chem{J}\cdot\chem{second}$$

### 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

• Prefixes are used to change the size of the unit.
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

• Mass is a measure of the resistance of an object to a change in its state of motion. Mass does not vary.
• Weight is the force that gravity exerts on an object. Weight varies with the strength of the gravitational field.

## Uncertainty in Measurement

### Uncertainty in measurements

• A digit that must be estimated in a measurement is called uncertain.
• A measurement always has some degree of uncertainty. It is dependent on the precision of the measuring device.
• Record the certain digits and the first uncertain digit (the estimated number).

### 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

### Precision and Accuracy

• Accuracy - Agreement of a particular value with the true value.
• Precision - Degree of agreement among several measurements of the same quantity.

## 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

• Exact numbers have an infinite number of significant figures.
• $$1\,\chem{inch}=2.54\,\chem{cm}$$, exactly (by definition).
• $$9$$ pencils (obtained by counting).

### Exponential Notation

• Example
• $$300.$$ written as $$3.00 \times 10^2$$
• Contains three significant figures.
• Number of significant figures can be easily indicated.
• Fewer zeros are needed to write a very large or very small number.

### 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?

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.

## Dimensional Analysis

### Converting between unit systems

• Use when converting a given result from one system of units to another.
• To convert from one unit to another, use the equivalence statement that relates the two units.
• Derive the appropriate unit factor by looking at the direction of the required change (to cancel the unwanted units).
• Multiply the quantity to be converted by the unit factor to give the quantity with the desired units.

### Example #1

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

• To convert from one unit to another, use the equivalence statement that relates the two units. $$1\,\chem{ft} = 12\,\chem{in}$$ The two unit factors are: $$\frac{1\,\chem{ft}}{12\,\chem{in}}\;\chem{and}\; \frac{12\,\chem{in}}{1\,\chem{ft}}$$

• Fahrenheit
• Celsius
• Kelvin

## Density

### Density

• Mass of substance per unit volume of the substance.
• Common units are $$\bfrac{\chem{g}}{\chem{cm^3}}$$ or $$\bfrac{\chem{g}}{\chem{mL}}$$.
$$\chem{Density}=\frac{\chem{mass}}{\chem{volume}}$$

## Classification of Matter

### Matter

• Anything occupying space and having mass.
• Matter exists in three states.
• Solid
• Liquid
• Gas

### The Phases - Macroscopically

• Solid
• Rigid
• Has fixed volume and shape.
• Liquid
• Has definite volume but no specific shape.
• Assumes shape of container.
• Gas
• Has no fixed volume or shape.
• Takes on the shape and volume of its container.

### Mixtures

Have variable composition.

• Homogeneous mixture - Having visibly indistinguishable parts; solution.
• Heterogeneous mixture - Having visibly distinguishable parts.

### Concept Check!

Which of the following is a homogeneous mixture?

• Pure water
• Gasoline
• Jar of jelly beans
• Soil
• Copper metal

Which of the following is a homogeneous mixture?

• Pure water
• Gasoline
• Jar of jelly beans
• Soil
• Copper metal

### Physical Change

• Change in the form of a substance, not in its chemical composition.
• Example: boiling or freezing water
• Can be used to separate a mixture into pure compounds, but it will not break compounds into elements.
• Distillation
• Filtration
• Chromatography

### Chemical Change

• A given substance becomes a new substance or substances with different properties and different composition.
• Example: Bunsen burner (methane reacts with oxygen to form carbon dioxide and water)

### Concept Check!

Which of the following are examples of a chemical change?

• Pulverizing (crushing) rock salt
• Burning of wood
• Dissolving of sugar in water
• Melting a popsicle on a warm summer day