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Chapter 3 Scientific 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 Notation We 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.

Practice a. 66 b. 222 c. 0.00046 d..08 e. 602,214,000,000,000,000,000,00 0 f. 0.0000000546 g. 56,938 h. 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 Figures 1. 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.)

Practice a. 123 b. 9.8000 x 10 4 c. 40,506 d. 22 e. 0.07080 f. 98,000 g. 0.00700 h. 0.000000000000144

More Practice a. 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 PrefixFactor Mega (M)10 6 Kilo (k)10 3 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 Mass Common 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 (-273 º C) 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

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