regents chemistry chapter 1: the science of chemistry
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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
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