Atomic Origins. Slide 1 / 20. Slide 2 / 20. Slide 3 / 20. Observing Chemical Reactions Lab. Thoughts on the Nature of Matter

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1 Slide 1 / 20 Slide 2 / 20 Atomic Origins Observing Chemical Reactions Lab Thoughts on the Nature of Matter Slide 3 / 20 Since ancient times, humans have pondered the nature of matter. Thousands of years ago, some humans speculated all matter was made up of some combination of four "elements" Earth Air Fire Water According to this theory, every unique substance would be made up of different combinations of the 4 elements.

2 The Idea of the Atom Slide 4 / 20 In ancient Greece (460 BC to 370 BC) a philosopher named Democritus formulated what is thought to be the first atomic theory. Democritus reasoned that matter must be made up of tiny, indivisible spheres he called "atomos" (Greek for indivisible) moving through empty space. He was right, atoms are small! If you made a tiny dot with the tip of a sharp graphite pencil, guess how many atoms of carbon would be in that dot? The Idea of the Atom Slide 4 (Answer) / 20 In ancient Greece (460 BC to 370 BC) a philosopher named Democritus formulated what is thought to be the first atomic theory. Democritus reasoned that matter must be made up of tiny, indivisible spheres he called "atomos" (Greek for indivisible) moving through empty space. Answer 4x10 24 atoms [This object is a pull tab] He was right, atoms are small! If you made a tiny dot with the tip of a sharp graphite pencil, guess how many atoms of carbon would be in that dot? Alchemy Slide 5 / 20 It would be almost 2000 years from the time of Democritus for humans to prove atoms are the building blocks of matter. In the meantime, the study of alchemy was a major precursor to modern chemistry. Alchemists tried to transform matter to convert base metals into gold or create powerful potions. + Isaac Newton famously practiced alchemy, attempting to turn substances into gold. As we now know, elements like gold can only be formed in the intense heat and pressure of exploding stars.

3 Chemistry Slide 6 / 20 Through controlled experiments and observation, alchemy evolved into the branch of science we know as chemistry. By the 1800's a couple of major principles had been established: Law of Conservation of Mass For any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant or be conserved over time. The law implies that mass can neither be created nor destroyed but it can change forms. Atomic Theory Matter is composed of atoms In a chemical reaction, atoms are not created or destroyed, but are rearranged. John Dalton In 1808 John Dalton published his atomic theory. It contained 6 postulates: 1. All matter consists of indivisible particles called atoms. 2. Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements. 3. Atoms cannot be created or destroyed. 4. Atoms of different elements may combine with each other in a fixed, simple, whole number ratios to form compound atoms. 5. Atoms of same element can combine in more than one ratio to form two or more compounds. 6. The atom is the smallest unit of matter that can take part in a chemical reaction. Slide 7 / 20 John Dalton Slide 8 / 20 Many of Dalton s findings are consistent with modern scientific theory, but some of his postulates have been disproved. For example, it turns out atoms are divisible! What are the parts of an atom called?

4 Chemical Changes Slide 9 / 20 Dalton arrived at his theory by gathering data from chemical reactions. During a chemical reaction a substance or substances can be transformed into chemically different substances. Common indications include of a chemical reaction include: A change in temperature such as wood burning or fireworks exploding A change in color such as metal rusting The production of an odor such as an egg rotting The formation a precipitate (a solid formed when two liquids are combined) The formation of bubbles (gas) such as the carbon dioxide that makes bread rise Physical Changes Slide 10 / 20 In some cases the properties of a substance may change, although the substance remains the same. These changes are called physical changes. For example, water can be turned from a free flowing liquid into a hard cube (ice). Its properties have changed but it s still water! Examples of physical changes include: Changes in texture such as sanding wood Changes in shape such as pulling metal into wires Changes in state (freezing, melting, boiling, condensing) Objectives Slide 11 / 20 The goals of this lab are to: Observe a number chemical reactions. Outline the indications that a chemical reaction has occurred while observing the chemical reactions in this lab. Outline those changes in properties or changes in energy that result from the chemical reactions you observe. Differentiate between a physical and a chemical change.

5 Materials Slide 12 / 20 Acetate sheet, reaction grid, goggles and aprons The following solutions with their designations A. 1 M hydrochloric acid B. 0.1 M copper (II) sulfate C. 0.1 M potassium iodide D. 0.1 M lead (II) nitrate E. Mossy zinc metal or zinc chips Slide 13 / 20 Guided Lab - Procedure and Examples Safety Warning: Slide 14 / 20 Always wear your goggles and aprons while completing this lab. Also wear your goggles and aprons when you're near someone working with chemicals. Familiarize yourself with the location of the eyewash and the emergency shower in the room. If you get any chemicals in your eye, use the eyewash. If any of the chemicals come in contact with your skin rinse them off immediately with lots of water and let the instructor know what you spilled --- on your way to rinsing them off. Never mix chemicals that you haven't been told to mix. Tell the instructor of any accidents immediately. Keep food and drinks out of the laboratory work area.

6 Procedure Slide 15 / 20 Identify the two chemicals to be mixed for a given trial. Mix the two chemicals for a given trial on the actetate sheet which has been clipped to a reaction grid, make observations and note these observations on your lab sheet. Data Collection Slide 16 / 20 After you mixed each set of chemicals note your observations. After you have mixed your last set of chemicals, review all the reactions that you completed to see if there are any new changes. Some chemical reactions are slow and you may be surprised by what you will see after some time has passed. Slide 17 / 20 Analysis Questions

7 1 Which of the following is not a chemical change? A iron rusting B paper burning C milk souring D sugar dissolving Slide 18 / 20 2 A change in physical properties always occurs when there is a chemical reaction? Slide 19 / 20 Yes No 3 When an egg is boiled its physical properties change. Students type their answers here Describe the changes in its physical properties. Slide 20 / 20