Unit 1 Notes The Metric System Easier to use because it is a decimal system. Every conversion is by...

Unit 1 Notes

The Metric SystemEasier to use because it is a decimal system.Every conversion is by some power of 10.• A metric unit has two parts.• A prefix and a base unit.• prefix tells you how many times to divide or multiply

by 10.• Example:

• centimeter

prefix Base unit

A centimeter= one hundredth of a meter

The Fundamental SI Units (le Système International, SI)

Physical Quantity Name Abbreviation Mass kilogram kg Length meter m Volume Liter L Temperature Kelvin K Amount of Substance

mole mol

Short cut to Converting

how far you have to move on this chart, tells you how far, and which direction to move the decimal place.

The box is the base unit, meters, Liters, grams, etc.

k h D d c m

Short cut to Conversion

Change 5.6 m to millimeters

k h D d c m

starts at the base unit and move three to the right.move the decimal point three to the right

56 00

MEASUREMENTAccuracy and Precision

Types of Measurement

• Quantitative- use numbers to describe• Qualitative- use description without numbers• 4 feet• extra large• Hot• 100ºF

Scientists prefer

Quantitative- easy check.Easy to agree upon, no personal bias.The measuring instrument limits how good the measurement is.

Accuracy vs. Precision• Accuracy - how close a measurement is to the accepted

value

• Precision - how close a series of measurements are to each other

ACCURATE = CORRECTPRECISE = CONSISTENT

Accuracy…

• To determine if data is accurate, ask yourself, “how close is this data point to the actual, accepted, or true value?

• In short, the closer your data is to the accepted or true value, the more accurate your data is.

Precision…

•To determine if your data is precise, ask yourself, “How close are my data points to one another?”

• In short, the closer your

data points are to one another, the more precise your data points are.

Sketch these in your journal…

AccuratePrecise

Not AccuratePrecise

Not AccurateNot Precise

AccurateNot Precise

Differences

Accuracy can be true of an individual measurement or the average of several.

Precision requires several measurements before anything can be said about it.

Percent Error

Indicates accuracy of a measurement

100literature

literaturealexperimenterror %

your value

accepted value

Percent ErrorA student determines the density of a substance to be

1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.

100g/mL 1.36

g/mL 1.36g/mL 1.40error %

% error = 2.9 %

MeasurementsWhen we measure something, we can (and do)

always estimate between the smallest marks.

21 3 4 5

MeasurementsThe better the marks, the better we can estimate.Scientist always understand that the last number

measured is actually an estimate.

21 3 4 5

Significant FiguresIndicate precision of a measurement.Recording significant figures

Significant figures in a measurement include the known digits plus a final estimated digit

2.35 cm

Significant FiguresCounting Sig Figs

Count all numbers EXCEPT:Leading zeros -- 0.0025Trailing zeros without

a decimal point -- 2,500

Rules for Counting Significant Figures - Details

• Exact numbers have an infinite number of significant figures.

•1 inch = 2.54 cm, exactly

4. 0.080

3. 5,280

2. 402

1. 23.50

Significant FiguresCounting Sig Fig Examples

4 sig figs

3 sig figs

3 sig figs

2 sig figs

Rounding rules

• Look at the number behind the one you’re rounding.• If it is 0 to 4 don’t change it.• If it is 5 to 9 make it one bigger.• Round 45.462 to four sig figs.

In science, we deal with some very LARGE numbers:

1 mole = 602,000,000,000,000,000,000,000 particles

In science, we deal with some very SMALL numbers:Mass of an electron =0.000000000000000000000000000000091 kg

Scientific Notation

Imagine the difficulty of calculating the mass of 1 mole of electrons!

0.000000000000000000000000000000091 kg x 602000000000000000000000 ???????????????????????????????????

Scientific Notation:A method of representing very large or very small numbers in the form:

M x 10n

M is a number between 1 and 10 n is an integer

2 500 000 000

Step #1: Insert an understood decimal point

.

Step #2: Decide where the decimal must end up so that one number is to its left

Step #3: Count how many places you bounce the decimal point

123456789

Step #4: Re-write in the form M x 10n

2.5 x 109

The exponent is the number of places we moved the decimal.

0.0000579

Step #2: Decide where the decimal must end up so that one number is to its leftStep #3: Count how many places you bounce the decimal pointStep #4: Re-write in the form M x 10n

1 2 3 4 5

5.79 x 10-5

The exponent is negative because the number we started with was less than 1.

Scientific Notation

• Converting into Sci. Notation:• Move decimal until there’s 1 digit to its left. Places moved

= exponent.• Large # (>1) positive exponent

Small # (<1) negative exponent• Only include sig figs.

65,000 kg 6.5 × 104 kg

Physical PropertiesA characteristic that can be observed or

measured without changing the identity of the substance

States of Matter

States of Matter• Solids

very low kinetic energy - particles vibrate but can’t move around

Retains size and shapeDefinite shape and volume

States of Matter• Liquids

low kinetic energy - particles can move around but are still close together

Takes the shape of its container

definite volume

States of Matter• Gases

high KE - particles can separate and move throughout container

Easily compressedNo definite shapeNo definite volume

Some Properties of Solids, Liquids, and Gases

Property Solid Liquid Gas

Shape Has definite shape Takes the shape of Takes the shape the container of its container

Volume Has a definite volume Has a definite volume Fills the volume of the container

Arrangement of Fixed, very close Random, close Random, far apartParticles

Interactions between Very strong Strong Essentially noneparticles

Physical ChangeA change in a substance that does not involve a change in the identity of the substance.

Examples:Phase Changes – boiling point, melting point, freezing point

A substance dissolving in another substance - solubility

Chemical Properties• Relates to a substance’s

ability to undergo change that transforms it into a different substance

Ability to : combust, oxidize, neutralize, reactivity, etc.

Chemical ChangeA change in which one or more substances are converted into different substances.

Evidence of Chemical Change: Heat and light Change in color Production of gas Precipitation of a solid

Temperature is Average Kinetic Energy

Fast Slow“HOT” “COLD”

Celcius & Kelvin Temperature Scales

Measuring Temperature

• Kelvin starts at absolute zero (-273 º C)• degrees are the same size• C = K -273• K = C + 273• Kelvin is always bigger.• Kelvin can never be negative.

273 K