Chapter 3Scientific Measurement

Ms. Wang

Lawndale High School

Measurement A quantity that has both a number and a unit

• It is important to be able to make measurements and decide whether a measurement is correct

Scientific NotationWe will be working with rather small and

large numbers in our science class.

For example, Avogadro's number is 602,214,000,000,000,000,000,000 and a human hair is .0002 meters in diameter. It will be much easier writing values in scientific notation, rather than standard form.

Scientific Notation• Scientific notation – a given

number written as the product of two numbers • a coefficient and 10 raised to a power

Rules for Scientific Notation

1. The first number is always between 1 and 9.9999...

2. Multiply the first number by 10 raised to an exponent.

• If you move the decimal to the right, the exponent is negative.

• If you move the decimal to the left, the exponent is positive.

Practicea. 66b. 222c. 0.00046d. .08e. 602,214,000,000,000,000,000,00

0f. 0.0000000546g. 56,938h. 0.000000000000144

Scientific Figures Significant Figures are VERY

important in chemistry.

Each recorded measurement has a certain number of significant digits. Any digit that is actually measured or estimated will be considered significant.

Placeholders, or digits that have not been measured or estimated, are not considered significant.

Rules for Significant Figures1. Digits from 1 to 9 are always significant.

(Example: 458kg has 3 sig. fig.)

2. Zeros between two other significant digits are always significant. (Example: 5057L has 4 sig. fig.)

3. One or more additional zeros to the right of both the decimal place and another significant digit are significant.

(Example: 5.00 has 3 sig. fig.)

4. Zeros used solely for spacing the decimal point (placeholders) are not significant. (Example: 0.007 has 1 sig. fig.)

Practicea. 123b. 9.8000 x 104

c. 40,506d. 22e. 0.07080f. 98,000g. 0.00700h. 0.000000000000144

More Practicea. 0.05730

b. 0.00073

c. 8765

d. 40.007

e. 143

f. 0.074

g. 1.072

h. 8.750 x 10-2

International System of Units

The five basic SI units used by chemists are…

Meter (length)

Kilogram (mass)

Kelvin (temperature)

Second (time)

Mole (amount of substance)

Commonly Used Metric Prefixes

Prefix Factor

Mega (M) 106

Kilo (k) 103

Deci (d) 10-1

Centi (c) 10-2

Milli (m) 10-3

Micro (u) 10-6

Nano (n) 10-9

Pico (p) 10-12

Units of Length

Common metric units of length include the

centimeter, meter, and kilometer

Units of Volume

Common metric units of volume include the liter,

milliliter, cubic centimeter, and

microliter

Units of MassCommon metric units of mass

include the kilogram, gram, milligram, and microgram

Weight is a force that measures the pull on a given mass by gravity

Units of Temperature Measures how hot or cold an object is The two commonly used units for

temperature are Celsius and Kelvin The zero point on the Kelvin scale is

called Absolute Zero (-273ºC)

K = °C +273

Units of Energy

Joule and Calorie are two common units of energy

1 calorie = 4.184 Joules

Density

The density of a substance generally decreases as its temperature increases

Density = mass/volume

Density is an intensive property that depends only on the composition of a substance, not on the size of the sample