1. The International System of Units

2. Lesson Objectives
Identify the seven base units of the International System of Units.
Know the commonly used metric prefixes.
Convert between the Celsius and Kelvin temperature scales.
Understand volume and energy as combinations of SI Units.
Distinguish between mass and weight.

3. SI Base Unit
All measurements depend on the use of units that are well known and understood. The English system of measurement units (inches, feet, ounces, etc.) is not used in science because of the difficulty in converting from one unit to another. The metric system is used because all metric units are based on multiples of 10, making conversions very simple. The metric system was originally established in France in The International System of Units is a system of measurement based on the metric system.

4. The acronym SI is commonly used to refer to this system and stands for the French term, Le Système International d’Unités. The SI was adopted by international agreement in and is composed of seven base units.
Quantity
SI Base Unit
Symbol
Length
meter m
Mass
kilogram kg
Temperature
kelvin K
Time
second s
Amount of a Substance
mole
mol
Electric Current
ampere A
Luminous Intensity
candela cd

5. The first five units are frequently encountered in chemistry
The first five units are frequently encountered in chemistry. The amount of a substance, the mole, will be discussed in detail in a later chapter. All other measurement quantities, such as volume, force, and energy, can be derived from these seven base units.

6. Metric Prefixes and Scientific Notation
As stated earlier, conversions between metric system units are straightforward because the system is based on powers of ten. For example, meters, centimeters, and millimeters are all metric units of length. There are 10 millimeters in 1 centimeter and 100 centimeters in 1 meter. Prefixes are used to distinguish between units of different size.

7. Listed below are the most common metric prefixes and their relationship to the central unit, which has no prefix. Length is used as an example to demonstrate the relative size of each prefixed unit.
Prefix
Unit Abbreviation
Exponential Factor
Meaning
Example
giga G
109
1,000,000,000
1 gigameter (Gm) =
109 m
mega M
106
1,000,000
1 megameter (Mm)
= 106 m
kilo k
103
1000
1 kilometer (km) =
1000 m
hecto h
102
100
1 hectometer (hm) =
100 m
deka da
101 10
1 dekameter (dam)
= 10 m 1
1 meter (m)

8. Prefix
Unit Abbreviation
Exponential Factor
Meaning
Example
deci d
10−1
1/10
1 decimeter (dm) =
0.1 m
centi c
10−2
1/100
1 centimeter (cm) =
0.01 m
milli m
10−3
1/1000
1 millimeter (mm) =
0.001 m
micro
10−6
1/1,000,000
1 micrometer (µm)
= 10−6 m
nano n
10−9
1/1,000,000,000
1 nanometer (nm) =
10−9 m
pico p
10−12
1/1,000,000,000,000
1 picometer (pm) =
10−12 m

9. There are more prefixes, although some of them are rarely used
There are more prefixes, although some of them are rarely used. Have you ever heard of a zeptometer?

10. The previous tables introduce a very useful tool for working with numbers that are either very large or very small. Scientific notation is a way to express numbers as the product of two numbers: a coefficient and the number 10 raised to a power. As an example, the distance from Earth to the Sun is about 150,000,000,000 meters—a very large distance indeed. In scientific notation, the distance is written as 1.5 × 1011 m. The coefficient is 1.5 and must be a number greater than or equal to 1 and less than 10. The power of 10, or exponent, is 11. Pictured below are two more examples of scientific notation.
The sun is very large and very distant, so solar data is better expressed in scientific notation. The mass of the sun is 2.0 × 1030 kg, and its diameter is 1.4 × 109 m.

11. Very small numbers, which we will be using a lot in this class, can also be expressed using scientific notation. The mass of an electron in decimal notation is grams. In scientific notation, the mass is expressed as 9.11 × 10−28 g. Notice that the value of the exponent is chosen so that the coefficient is between 1 and 10.

12. Typical Units in Chemistry
Length and Volume
The SI basic unit of length, or linear measure, is the meter (m). All measurements of length may be made in meters, though the prefixes listed previously will often be more convenient. The width of a room may be expressed as about 5 meters (m), whereas a large distance such as the distance between New York City and Chicago is better expressed as 1150 kilometers (km). Very small distances can be expressed in units such as the millimeter or the micrometer. The width of a typical human hair is about 20 micrometers (µm).

13. Volume is the amount of space occupied by a sample of matter
Volume is the amount of space occupied by a sample of matter. The volume of a regular object can be calculated by multiplying its length by its width by its height. Since each of those is a linear measurement, we say that units of volume are derived from units of length. The SI unit of volume is the cubic meter (m3), which is the volume occupied by a cube that measures 1 m on each side. This very large volume is not very convenient for typical use in a chemistry laboratory. A liter (L) is the volume of a cube that measures 10 cm on each side.

14. Mass is a measure of the amount of matter that an object contains
Mass is a measure of the amount of matter that an object contains. The mass of an object is made in comparison to the standard mass of 1 kilogram. The kilogram was originally defined as the mass of 1 L of liquid water at 4°C (the volume of a liquid changes slightly with temperature). In the laboratory, mass is measured with a balance, which must be calibrated with a standard mass so that its measurements are accurate.
Mass and Weight

15. Temperature and Energy
Touch the top of the stove after it has been on and it feels hot. Hold an ice cube in your hand and it feels cold. Why? The particles of matter in a hot object are moving much faster than the particles of matter in a cold object. Hold out your two hands. Place one on the table top and compare temperatures. Do you feel a difference?

16. An object’s kinetic energy is the energy due to motion
An object’s kinetic energy is the energy due to motion. The particles of matter that make up the hot stove have a greater amount of kinetic energy than those in the ice cube. Temperature is a measure of the average kinetic energy of the particles in matter. In everyday usage, temperature is how hot or cold an object is. Temperature determines the direction of heat transfer. When two objects at different temperatures are brought into contact with one another, heat flows from the object at the higher temperature to the object at the lower temperature. This occurs until their temperatures are the same.

17. Temperature can be measured with several different scales
Temperature can be measured with several different scales. The Fahrenheit scale is typically not used for scientific purposes. The Celsius scale of the metric system is named after Swedish astronomer Anders Celsius ( ). The Celsius scale sets the freezing point and boiling point of water at 0°C and 100°C, respectively. The distance between those two points is divided into 100 equal intervals, each of which is referred to as one degree.

18. The Kelvin temperature scale is named after Scottish physicist and mathematician Lord Kelvin ( ). It is based on molecular motion, with the temperature of 0 K, also known as absolute zero, being the point where all molecular motion ceases. The freezing point of water on the Kelvin scale is K, while the boiling point is K. As can be seen by the 100 kelvin difference between the two, a change of one degree on the Celsius scale is equivalent to the change of one kelvin on the Kelvin scale. Converting from one scale to another is easy, as you simply add or subtract
◦C = K−273.15
K = ◦C

19. Energy is defined as the capacity to do work or to produce heat
Energy is defined as the capacity to do work or to produce heat. As discussed previously, kinetic energy is one type of energy and is associated with motion. Another frequently encountered form of energy is potential energy, which is a type of energy that is stored in matter. The joule (J) is the SI unit of energy and is named after English physicist James Prescott Joule ( ). In terms of SI base units, a joule is equal to a kilogram times a meter squared divided by a second squared (kg•m2/s2). A common non-SI unit of energy that is often used is the calorie (cal), which is equal to J.

20. Lesson Summary
Measurements are critical to any field of science and must consist of a quantity and an appropriate unit. The International System of Units consists of seven base units.
The metric system utilizes prefixes and powers of 10 to make conversions between units easy.
Length (m), mass (kg), temperature (K), time (s), and amount (mol) are the base units that are most frequently used in chemistry. Quantities such as volume and energy can be derived from combinations of the base units.