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Unit 1: Introduction to Chemistry

Unit 1: Introduction to Chemistry. 1.1 What is Chemistry?. Chemistry - the study of substances and the changes they can undergo. EX: a match burning, how bleach removes stains , why bread dough rises, etc . The Central Science

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Unit 1: Introduction to Chemistry

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  1. Unit 1: Introduction to Chemistry

  2. 1.1 What is Chemistry? • Chemistry- the study of substances and the changes they can undergo. EX: a match burning, how bleach removes stains, why bread dough rises, etc. • The Central Science Chemistry overlaps into many other sciences: Biology, Geology, Astronomy, etc. • Chemicals are everywhere, in everything, and impact many different aspects of life. Chemistry, therefore, is considered a central science. Life, as we know it, is a product of what Chemistry and Physics has already done.

  3. B) Why Study Chemistry? • To help you understand the physical world around you. To develop skills for evaluation and critical thinking. Maybe even help prepare you for a job which requires chemistry. • (ex. occupations which require chemistry: Engineering, medical professionals, hair stylists, crime labs, cosmetic makers, drug developers, oil companies, Wine makers, Mc Donald’s, Candy makers, Photographers …)

  4. 1.2 The Scientific Method • Scientific Method- an orderly, systematic approach to gather knowledge. It is a way of answering questions about our observable world.

  5. Steps of the Scientific Method • Make an observation • State the question • Collect information • State a hypothesis • Design an experiment • Make observations • Collect, record and study data • Draw a conclusion

  6. Sci. Method Steps Explained Making an Observation Forming a Hypothesis This should be a possible, logical, answer to the question about your observation. It is typically expressed in a “cause-and-effect” format. A scientific hypothesis must be one which requires and can be tested by an experiment. If it does not… it is not “scientific”. Notice a natural event: the ball falls to the ground, the sky is blue, etc. This observation can be about almost anything! Once you’ve noticed something… form a question.

  7. Sci. Method Steps Explained Performing an Experiment Interpreting the Results Once the experiment is complete… you look at your data and the observations you made interpret what they tell you. Did you prove your hypothesis wrong? Did you learn anything new? (Experimental control) • For a hypothesis to be tested properly, you must design and perform an experiment which examines ONE variable at a time. If you have more than one variable the results will not be conclusive and very little knowledge will be gained.

  8. Laws and Theories Law Theory an explanation of a set of related observations or events based upon proven hypotheses and verified multiple times by detached groups of researchers. One scientist cannot create a theory; he can only create a hypothesis. THEY EXPLAIN AND PREDICT EVENTS. • a statement of fact meant to explicate, in concise terms, an action or set of actions. It is generally accepted to be true and universal, and can sometimes be expressed in terms of a single mathematical equation. THEY TELL WHAT HAPPENED.

  9. 1.4 Units of Measurement • The International System of Units • In 1960, at a scientific conference on units held in France, the SI system of units were internationally accepted for the scientific community. The SI system is based on the metric system and we refer to these as base units.

  10. BASE UNITS

  11. Meter- defined as the distance that light travels in a vacuum during a time interval of 1/299,792,458 of a second. • Mass- amount of matter in an object. 1 kg = 2.2 lbs (on earth). • Weight-equals the force of gravity pulling on the object. • Derived units- a combination of 2(+) base units = a new unit.

  12. DERIVED UNITS

  13. Area- length X width = m X m= m2 Volume- the amount of space that an object occupies. Length X width X height = m X m X m= m3 EXCEPTIONS… The liter (L)- the common unit for volume. 1mL= 1cm3 Celsius (C)- common unit for temperature 1K = (273 + C)

  14. Metric Prefixes • Prefix- a word attached to the front of the base unit. The SI prefixes are base 10 and, therefore, increase and decrease by 10’s.

  15. Converting among prefixes • When converting from one prefix to another, remember this saying: • King Henry Died By Drinking Chocolate Milk. • When set up as such: • k h da _ d c m • Now converting among prefixes is just a matter of pushing the decimal

  16. 1.5 Working with Numbers • Significant Digits • 1. Leading zeros are never significant. • 2. Imbedded zeros are always significant. • 3. Trailing zeros are significant only if the decimal point is specified. Hint: Change the number to scientific notation. It is easier to see.

  17. EXAMPLES:

  18. Addition & Subtraction:The last digit retained is set by the first doubtful digit.

  19. Multiplication or Division:The answer contains no more significant figures than the least accurately known number.

  20. Scientific Notation • Chemists often work with numbers that are extremely large or extremely small. • For example, there are 10,300,000,000,000,000,000,000 carbon atoms in a 1-carat diamond each of which has a mass of 0.000,000,000,000,000,000,000,020 grams. It is impossible to multiply these numbers with most calculators because they can't accept either number as it is written here. • To do a calculation like this, it is necessary to express these numbers in scientific notation, as a number between 1 and 10 multiplied by 10 raised to some exponent.

  21. *Exponent Review Some of the basics of exponential mathematics are given below. • Any number raised to the zero power is equal to 1. 10= 1 100= 1 • Any number raised to the first power is equal to itself. 11 = 1 101 = 10 • Any number raised to the nth power is equal to the product of that number times itself n-1 times. 22 = 2 x 2 = 4 105 = 10 x 10 x 10 x 10 x 10 = 100,000 • Dividing by a number raised to an exponent is the same as multiplying by that number raised to an exponent of the opposite sign.

  22. Converting to Scientific Notation The following rule can be used to convert numbers into scientific notation: The exponent in scientific notation is equal to the number of times the decimal point must be moved to produce a number between 1 and 10. • Ex. In 1990 the population of Chicago was 6,070,000. To convert this number to scientific notation we move the decimal point to the left six times. • 6,070,000 = 6.070 x 106

  23. To convert numbers larger than 1, we will move the decimal point to the left. For example, 10,300,000,000,000,000,000,000 carbon atoms into scientific notation, we move the decimal point to the left 22 times. • 10,300,000,000,000,000,000,000 = 1.03 x 1022

  24. To convert numbers smaller than 1 into scientific notation, we have to move the decimal point to the right. The decimal point in 0.000985, for example, must be moved to the right four times. • 0.000985 = 9.85 x 10-4

  25. The primary reason for converting numbers into scientific notation is to make calculations with unusually large or small numbers less cumbersome. Because zeros are no longer used to set the decimal point, all of the digits in a number in scientific notation are significant, as shown by the following examples.

  26. Ratios • Units found by dividing one unit by another.  (The speedometer in your car registers the ratio of miles/hour.) The most common ratio in chemistry is density (g/ml or g/cm3).Density is calculated by this formula: density = mass/volume • Lets say you had an object that’s mass was 20g and its volume was 10cm3.  How would you calculate the density? • Density = mass/volume = 20g/10cm3 = 2g/cm3 • If you are given the mass and the density can you calculate volume? • Yes!  Density = mass/volume ► volume = mass/density.

  27. 1.6 Problem Solving • Dimensional Analysis- technique of converting between units.  Unit equalities show how different units are related (1g=100cm).  Conversion factors are written from the unit equalities.  The conversion factor is set up so that the bottom number cancels the given unit and a new unit is created.  • Example:  Convert 10 cm to inches. Conversion factors (1m = 100 cm)   (1m = 39.37inches) • Start with the given unit, then use you conversion factors to cancel units until to arrive at the unit you want to convert to.

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