Regents Chemistry

1. Regents Chemistry • Chapter 1: The Science of Chemistry

2. 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!

3. 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

4. Mixtures • For Example: Elements, which are pure substances. Can you name one? AIR Compounds, which are pure Substances Can you name one? Mixture of oxygen nitrogen, carbon dioxide Argon, water, others

5. 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

6. ElementsElements 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

7. 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

8. CompoundsCompounds 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...

9. Good Old H2O 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.

10. 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

11. 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

12. 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

14. Identify each of the following.. End

15. 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

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

17. Scientific Notation • In order to use this system, we must first understand scientific notation • Why do we use it? BIG THINGS Very Small things...

18. 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 = 100x 10 = 1000 AND Example: 1.0 / 10 = 0.10 / 10 = 0.010 / 10 = 0.0010

19. 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

20. 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 exponent and is written EE on your calculator!

21. 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!

22. The Powers of 10 1 0 0 0 3 moves to the right gives a positive exponent 1.0 x 103 = 1000 also!

23. Moves to the right make a number larger... • But what about moves to the left? 1.0 The number gets smaller!

24. 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!

25. 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

26. 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

27. Practice Problems • Convert to regular numbers 2.3 x 105 5.3 x 103 6.75 x 10-4 3.19 x 10-9 230,000 5300 0.000675 0.00000000319

28. Dealing with positive exponents Count the moves and see! • 3.0 x 105 also equals 300,000 300,000 number gets smaller, so we need more of a positive exponent to make an equal value number gets larger, so we need less of a positive exponent to make an equal value 0.30 x 106 30.0 x 104

29. Dealing with negative exponents • 3.0 x 10-5 also equals 0.00003 0.00003 Count the moves and see! number gets larger, so we need less of a negative exponent to make an equal value We are moving closer to the decimal point! number gets smaller, so we need more of a negative exponent to make an equal value. We are moving further from the decimal point! 0.30 x 10-4 30.0 x 10-6 0.00003 0.00003

30. Practice Problems 0.15 x 104 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? 200 x 103 0.36 x 10-2 5500 x 10-8 End

31. Regents Chemistry • Significant Figures

32. 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

33. Significant Figures…Why? • Allow us to make an accurate measurement! • Contain certain numbers and one uncertain number

34. Certain Numbers • Same regardless of who made the measurement • Actual divisions marked on instrument • Example: Ruler, beaker

35. Uncertain Numbers • Are an estimate • Vary by person and trial • For example: estimate with a ruler, beaker

36. 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 ruler you must make an estimate!

37. 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

38. 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

39. Rounding Numbers and Sig Figs • Less than 5 • Equal to/more than 5 End

40. 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 cm 31.75 cm = 31.8 cm = 1 in But you must consider sig figs, so

41. What about more than 1 conversion? • Given: 1 kg = 103 g and 1g = 10-6 g • Problem: Convert 5 kg to g • Two methods: 103 – 10-6 equals 1 g 103 g 5 kg = 3 - - 6 = 9 1 kg 10-6g So your final answer is 5 x 109g You can simply use your calculator  EE button Learn the simple rules of math with scientific notation end