1. An introduction to Chemistry

2. Why is Chemistry Important? Used in many professions Used to create new clean sources of energy Understand and control diseases Used to help the environment Improves problem solving skills

3. Chemistry: an Introduction Chemistry =A branch of physical science that studies the composition, structure, properties and change of matter. matter = anything that occupies space and has a mass

4. Chemistry Most of the phenomena that occur around us involve chemical reactions: Burning wood or other materials Rust Baking Digestion

5. Experiment & Explanation - experiment is the heart of chemistry and chemistry exploration Experiment = an observation of natural phenomena carried out in a controlled manner so that the results can be duplicated and rational conclusions obtained

6. Experiment - must control everything except one variable - must be able to duplicate results over and over - change more than one variable = no conclusions can be drawn (NOT an experiment)

7. Law Law = a statement that expresses observed behavior - Tells what happened

8. Hypothesis - during research, scientists try to make sense of their observations by devising an explanation - explanations organize thoughts and predict future events - a good hypothesis will suggest other experiments hypothesis - a tentative explanation of some regularity in nature (NOT AN EDUCATED GUESS)

9. Theory - if a hypothesis successfully passes MANY tests it becomes known as a theory Theory = a tested explanation of basic natural phenomena - cannot be proven absolutely - hold true with the given technology and knowledge

10. Matter: Physical State Three States! 1. solids = the form of matter characterized by rigidity; incompressible and has a fixed volume and shape

11. Matter: Physical State 2. Liquid = the form of matter that is relatively incompressible fluid; fixed volume no fixed shape

12. Matter: Physical State 3. gas = the form of matter that is easily compressible fluid; no fixed volume or shape

13. Matter: Physical State

14. Elements and Compounds - before you can define the difference must first look at a) physical change b) chemical change

15. Physical Change physical change = a change in the form of matter but not in its chemical identity Examples 1. change in physical state (solid to liquid) 2. dissolving one substance in another 3. can be separated physical property = a characteristic that can be observed for a material without changing its chemical identity

16. Chemical Change Chemical change = a change in which one more more kinds of matter are transformed into a new kinds of matter or several new kinds of matter Examples: a rusting car, burning a piece of paper… chemical property = a characteristic of a material involving its chemical change (ABILITY to react: i.e. the ability for paper to burn

17. Signs of a chemical change 1. production of an odor 2. change in temperature 3. change in color 4. formation of bubbles 5. formation of a solid (precipitate)

18. Chemical or Physical? Practice Problems: 1. burning wood in the back yard 2. tearing a piece of paper in half 3. boiling water until it evaporates 4. melting butter

19. Law of Conservation of Mass mass = the quantity of matter in a material - usually measured with a balance Law of Conservation of Mass = the total mass remains the same during a chemical change; mass cannot be created nor destroyed

20. Example Problem You heat 2.53 grams of metallic mercury in air, which produces 2.73 grams of a red-orange residue. Mercury + air ----> red-orange residue What is the mass of oxygen that reacts?

21. Homework! Conservation of Mass Worksheet

22. Homework Physical versus Chemical Worksheet

23. Pure Substance -Always has the same composition -Either an element or a compound -Unique set of physical properties by which it can be recognized -Cannot be separated by an physical techniques

24. Mixtures -One or more substance added together -Can be separated - has variable composition Two types -Heterogeneous mixture -Homogeneous mixture

25. Heterogeneous mixtures heterogeneous mixtures = a mixture that consists of physically distinct parts, each with different properties Examples:

26. Homogeneous Mixtures homogeneous mixture = a mixture that is uniform in its properties throughout a given sample Examples:

27. Homogeneous Mixtures -Known as solutions -Alloy-Mixture of metals

28. Your turn! Homogenous or Heterogeneous? 1) Brass 4) soil 2) chex mix5) ocean water 3) Chocolate chip cookies6) kool-aid

29. Elements - small number of substances are elements elements = a substance that cannot be decomposed by any chemical reaction into simpler substances (118 elements currently- periodic table) examples: oxygen, nitrogen, sulfur, sodium…

31. Compounds compounds = a substance composed of two or more elements chemically combined i.e. water, carbon dioxide, sodium chloride -most substances are compounds -unlimited number of compounds can be formed

32. Your turn! Element or Compound? 1) nitrogen4) water 2) Carbon dioxide 5) carbon 3) oxygen6) sodium chloride

33. Homework States of Matter Worksheet