Regents Chemistry Chapter 1: The Science of Chemistry

What is Matter?

• Matter is the “stuff” of which the universe is composed..and comes in three states

• Anything that has mass and occupies space is considered matter!

Mixtures and Pure Substances

• A mixture is something that has variable composition. – Example: soil, cereal, air

• A pure substance will always have the same composition. Pure substances are elements or compounds.– Example: pure water, NaCl salt, carbon

Mixtures For Example:

AIR

Mixture of oxygennitrogen, carbon

dioxideArgon, water, others

Elements, which arepure substances. Can you name one?

Compounds,which are pure SubstancesCan you name one?

Elements and Compounds

Pure substances have an invariable composition and are composed of either elements or compounds.

Elements

"Substances which cannot be decomposed into simpler substances by chemical means".

Compounds

Can be decomposed into two or more elements.

For Example: Electrolysis of Water

Elements

Elements are the basic substances out of which all matter is composed.

Everything in the world is made up from only 110 different elements. 90% of the human body is composed of only three elements: Oxygen, Carbon and Hydrogen

Elements are known by common names as well as by their abbreviations (symbols).

Ne

Elements – early pioneers

Robert Boyle (1627 – 1691) – the first scientist to recognize the importance of careful measurements.

Defined the term element in terms of experimentation;

a substance was an element unless it could be broken down into two or more simpler substances

Compounds

Compounds are substances of two or more elements united chemically in definite proportions by mass.

The observation that the elemental composition of a pure compound is always the same is known as the law of constant composition (or the law of definite proportions).

For Example...

For example, pure water is composed of the elements hydrogen (H) and oxygen (O) at the defined ratio of 11 % hydrogen and 89 % oxygen by mass.

Good Old H2O

Classification of Mixtures Homogeneous Mixtures – are the same throughout (a

single phase). ex: table salt and water, air, brass

Heterogeneous Mixtures – contain regions that have different properties from those of other regions (more than 1 phase). ex: sand in water, cereal

Phase - area of uniform composition

Examples of Heterogeneous Mixtures

Sand on a beach Cereal sand in water Dirt Most of the time you can see the

different substances, hence the mixtures are said to be not well mixed and can be separated physically

Examples of Homogeneous Mixtures, also called Solutions

Air Table salt in water Solution of Na2SO4

You cannot see the different substances

in the mixture (solution) - can be separated by chemical or physical means

Identify each of the following..

End

The SI System and SI Metric Math

In 1960 a system abbreviated the SI system was introduced to provide a universal means to evaluate and measure matter. There are 7 base units

Prefixes

Base units can be too large or small for some measurements, so prefixes are added. See your reference table

Scientific Notation In order to use this system, we must first understand

scientific notation Why do we use it?

Very Small things... BIG THINGS

Scientific Notation

What can the number 10 do?

It can be used as a multiplier or a divider to make a number LARGER or smaller

Example: 1.0 x 10 = 10 x 10 = 100 x 10 = 1000

AND

Example: 1.0 / 10 = 0.10 / 10 = 0.010 / 10 = 0.0010

Scientific Notation

Scientific notation uses this principle…but…uses a shorthand form to move the

decimal point

The “shorthand” form is called THE POWERS OF 10

See Powers of 10 Animation

The Powers of 10

1.0 x 10 x 10 = 100…right?!

1.0 is multiplied twice by ten…

therefore 10 x 10 = 102

This is called an exponentand is written EE on your calculator!

The Powers of 10

Overall.. 1.0 x 10 x10 x 10 = 1.0 x 103 = 1000 We can also look at it a different way..

1000 has three zeros after the digit 1..so..

it takes three moves to the right to get to the end of the number!

The Powers of 10

1 0 0 0

3 moves to the right gives a positive exponent

1.0 x 103 = 1000 also!

Moves to the right make a number larger... But what about moves to the left?

1.0

The number gets smaller!

Moves to the left

0.01 = 2 moves from 1.0 to the left therefore..

1.0 x 10-2

The negatives sign means move decimal to the left!

The Powers of 10 Summary

Moves to the right are positive and

make a number larger!

Moves to the left are negative and

make a number smaller!

The number with the decimal > 9.99..etc

and cannot be smaller than 1.0

Practice Problems

Convert to Scientific Notation

10000

50000

565,000

0.0036

0.00000887

1 x 104

5 x 104

5.65 x 105

3.6 x 10-3

8.87 x 10-6

Convert to regular numbers

2.3 x 105

5.3 x 103

6.75 x 10-4

3.19 x 10-9

Practice Problems

230,0005300

0.000675

0.00000000319

Dealing with positive exponents

3.0 x 105 also equals 300,000

300,000number gets larger, so we need less of a positive exponent to make an equal value

number gets smaller, sowe need more of a positive exponent to make an equal value

0.30 x 106 30.0 x 104

Count the moves and

see!

Dealing with negative exponents 3.0 x 10-5 also equals 0.00003

0.00003number gets larger, so we need less of a negative exponent to make an equal valueWe are moving closer to the decimal point!

0.30 x 10-4

number gets smaller, sowe need more of a negative exponent to make an equal value.We are moving further from the decimal point!

30.0 x 10-6

Count the moves and

see!

0.00003 0.00003

Practice Problems

1.5 x 103 = 0.15 x 10?

2.0 x 105 = 200 x 10?

3.6 x 10-3 = 0.36 x 10?

5.5 x 10-5 = 5500 x 10?

0.15 x 104

200 x 103

0.36 x 10-2

5500 x 10-8

End

Regents Chemistry

Significant Figures

Five-minute Problem

How many significant figures are in the following: (write the number and answer)

125

1.256

0.0000004567

0.00300

1.004623

Significant Figures…Why?

Allow us to make an accurate measurement!

Contain certain numbers

and one uncertain number

Certain Numbers

Same regardless of who made the measurement

Actual divisions marked on instrument

Example: Ruler, beaker

Uncertain Numbers

Are an estimateVary by person and trialFor example: estimate with a

ruler, beaker

Significant Figures Include...

All certain numbers and one uncertain number

For example: 8.55 cm is actually

8.55 0.01+ -

The last digit is not actually on the ruleryou must make an estimate!

Rules for Counting Sig. Figs.

1. Nonzero integers - always count ex: 1322 has four significant figures

2. Zeros Leading Zeros - precede all nonzero digits

and do not count! Ex: 0.00025 Captive Zeros - fall between nonzero digits

and always count! Ex: 1.008 Trailing Zeros - zeros at end of number Ex. 100.

vs. 100

Significant only if the number contains a decimal

Rules for Counting Sig. Figs. 3. Exact Numbers - have an unlimited

amount of significant figures… 2 Kinds

Describe something…50 cars, 25 bugs

By definition… 1 in = 2.54 cm

Rounding Numbers and Sig Figs

Less than 5

Equal to/more than 5

End

Dimensional Analysis and conversions with the SI System Given: 1 in = 2.54 cm Problem: Convert 12.5 in to cm We use the parentheses method of DA

12.5 in 2.54 cm1 in

= 31.75 cm

But you must consider sig figs, so

= 31.8 cm

What about more than 1 conversion? Given: 1 kg = 103 g and 1g = 10-6 g Problem: Convert 5 kg to g Two methods:

5 kg1 kg

103 g

10-6g

1 g

You can simply use your calculator EE button

Learn the simple rules of math with scientific notation

=

103 – 10-6

equals

3 - - 6 = 9So your final answer is

5 x 109 g

end