
# Chapter 1 Matter and Energy

Shaun Williams, PhD

## Matter and its Classification

### Pure Substances

• Have uniform, or the same, chemical composition throughout and from sample to sample.
• Two kinds of pure substances
• Elements
• An element is a substance that cannot be broken down into simpler substances even by a chemical reaction.
• Elements are separated further into metals and nonmetals.
• Compounds
• A compound is a substance composed of two or more elements combined in definite proportions.

### Practice - Represntations of Matter

Identify the nonmetals in the following figure. Explain the characteristics you considered in making your decision.

### Representations of Matter

• Matter is composed of atoms.
• An atom is the smallest unit of an element that retains the chemical properties of that element.

### Representations of Matter 2

• Atoms can combine together to form molecules.
• Molecules are composed of two or more atoms bound together in a discrete arrangement.
• The atoms bound together in a molecule can be from the same element or from different elements.

### States of Matter

• Discuss the following questions with someone near you.
• How does a solid differ from a liquid?
• How does a gas differ from a liquid?
• How does a solid differ from a gas?

### States of Matter

Solid Liquid Gas
Fixed shape Shape of continaer (may or may not fill it) Shape of container (fills it)
Its own volume Its own volume Volume of container
No volume change under pressure Slight volume change under pressure Large volume change under pressure
Particles are fixed in place in a regular array Particles are randomly arranged and free to move about until they bump into one another Particles are widely separated and move independently of one another

### Symbols Used in Chemistry

• Elemental symbols
• a shorthand version of an element’s longer name
• can be 1-2 letters and can be derived from the Latin or Greek name [ex. $$\chem{Ag}$$]
• Chemical formulas
• describe the composition of a compound
• use the symbols for the elements in that compound [ex. $$\chem{H_2O}$$ and $$\chem{CO_2}$$]

### Symbols Used in Chemistry - Examples

Name Symbol
helium He
fluorine F
silver Ag
water $$\chem{H_2O}$$
carbon dioxide $$\chem{CO_2}$$
methane (natural gas) $$\chem{CH_4}$$

### Symbols Used in Chemistry - Phases

• Symbols for physical states
• are found in parenthesis by the elemental symbol or chemical formula
• designate the physical state [ex. solid, liquid, gas, aqueous]
• See table to the right
Name Symbol
solid (s)
liquid (l)
gas (g)
aqueous (dissolved in water) (aq)

## Physical and Chemical Changes and Properties of Matter

### Physical Properties of Matter

• Physical properties
• are properties that can be observed without changing the composition of the substance
• Four common physical properties are:
• mass
• volume
• density
• temperature

### Mass

• Mass:
• measures the quantity of matter
• is essentially the same physical quantity as weight, with the exception that weight is bound by gravity, mass is not
• common units are grams (g)

### Volume

• Volume:
• amount of space a substance occupies
• can be calculated by measuring the sides of a cube or rectangular side, then multiplying them $\chem{Volume = l \times w \times h}$
• common units are centimeters cubed ($$\chem{cm^3}$$) or milliliters ($$\chem{mL}$$)

### Density

• Density:
• the ratio of the mass to its volume $\chem{density = \frac{mass}{volume}}$
• units are $$\bfrac{g}{mL}$$ (solids and liquids) or $$\bfrac{g}{L}$$ (gases)
• See Table 1.4 for a listing of densities for common substances

### Temperature

• Temperature:
• a measure of how hot or cold something is relative to some standard
• is measured with a thermometer
• at which a phase change occurs is independent of sample size
• units are degrees Celsius ($$\chem{{}^\circ C}$$) and degrees Kelvin ($$\chem{K}$$) $\chem{T_K = T_{{}^\circ C} + 273.15}$ $\chem{T_{{}^\circ F} = 1.8 \left( T_{{}^\circ C} \right) + 32}$

### Physical Changes

• A physical change
• is a process that changes the physical properties of a substance without changing its chemical composition
• evidence of a physical change includes:
• a change of state
• Example: water changes from a solid to a gas
• an expected change in color

### Chemical Changes

• A chemical change
• is a process in which one or more substances are converted into one or more new substances
• also called a chemical reaction
• evidence of a chemical change includes:
• bubbling
• a permanent color change
• a sudden change in temperature

### Chemical Properties

• Defined by what it is composed of and what chemical changes it can undergo

## Energy and Energy Change

### What is Energy?

• Energy
• is the capacity to do work or to transfer heat
• Two main forms of energy are:
• Kinetic energy: the energy of motion
• Potential energy: energy possessed by an object because of its position
• Other energies are forms of kinetic and potential energy (chemical, mechanical, electrical, heat, etc.)

### Energy Units

• Units for energy are calories or joules $\chem{4.184\, J = 1\, cal}$
• A calorie is the amount of energy required to raise $$\chem{1\, g}$$ of water by $$\chem{1^\circ C}$$.
• A kilojoule (kJ) or 1000 joules (J) is approximately the amount of energy that is emitted when a kitchen match burns completely.

## The Scientific Method

### What is the scientific method?

• is an approach to asking questions and seeking answers that employs a variety of tools, techniques, and strategies
• The method generally includes observations, hypotheses, laws, and theories.

### Some parts of the scientific method

• Observations include:
• experimentation
• collection of data
• A hypothesis is a tentative explanation for the properties or behavior of matter that accounts for a set of observations and can be tested.
• A scientific law describes the way nature operates under a specified set of conditions.
• Theories explain why observations, hypotheses, or laws apply under many different circumstances.

## Math

### Scientific Notation

• A number written in scientific notation is expressed as: $C \times 10^n$ where $$C$$ is the coefficient (a number with only one digit to the left of the decimal point) and $$n$$ is the exponent (a positive or negative integer)
• Move the decimal point in the number until just one nonzero digit is to the left of the decimal point. The final number is $$C$$.
• The exponent on the 10 ($$n$$) is equal to the number of places moved the decimal point.
• If the decimal point is moved to the left, then $$n$$ is positive.
• If the decimal point is moved to the right, then $$n$$ is negative.

### Scientific Notation - Examples

Normal Notation Scientific Notation
3245. $$3.245 \times 10^3$$
0.000003245 $$3.245 \times 10^{-6}$$
3,245,000,000 $$3.245 \times 10^9$$
0.0050607 $$5.0607 \times 10^{-3}$$
88. $$8.8 \times 10^1$$
2.45 $$2.45 \times 10^0$$

### Significant Figures - Step 1

Here is a simpler method for determining the number of significant figures in a given measurement.

1. Underline the left-most nonzero digit.
• 273.1023
• 0.1023
• 10.025
• 1020

### Significant Figures - Step 2

1. Look for a written decimal point in the number.
1. If the number contains a decimal point, underline the right-most digit.
• 273.1023
• 0.1023
• 10.025
2. If the number does not contain a decimal point, underline the right-most nonzero digit.
• 1020

### Significant Figures - Step 3

1. Count the number between the underlined numbers (including those underlined)
• 273.1023 ← 7 sig. figs.
• 0.1023 ← 4 sig. figs.
• 10.025 ← 5 sig. figs.
• 1020 ← 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).

### 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. $$23.445 + 7.8\underline{3} = 31.275 \xrightarrow{\chem{round}} 31.2\underline{8}$$

### Units

• Measurement
• is the determination of the size of a particular quantity
• Measurements are defined by both a quantity (number) and unit.
• Most scientists use SI (from the French for Système Internationale) units (see top chart or chart on pg. 39).
Unit Symbol Quantity
meter m length
kilogram kg mass
second s time
ampere A electric current
Kelvin K temperature
mole mol amount of substance

### Units - Prefixes

• Scientists also use the metric system to define base units of measure, with the understanding that a special prefix denotes fractions or multiples of that base (see chart on right).
Prefix Factor Symbol
giga $$10^9$$G G
mega $$10^6$$ M
kilo $$10^3$$ k
deci $$10^{-1}$$ d
centi $$10^{-2}$$ c
milli $$10^{-3}$$ m
micro $$10^{-6}$$ μ
nano $$10^{-9}$$ n

### Unit Analysis

A possible approach to problem solving involves 4 steps:

1. Decide what the problem is asking for.
2. Decide what relationships exist between the information given in the problem and the desired quantity.
3. Set up the problem logically, using the relationships decided upon in step 2.
4. Check the answer to make sure it makes sense, both in magnitude and units.

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