Science 9 – Chemistry 2 Sci 924 – Sci 926

1. Science 9 – Chemistry 2Sci 924 – Sci 926

2. Quick Review • Law of Conservation of Mass review • In a chemical change, the total mass of the new substance is always the same as the total mass of the original substance. • Law of Definite Composition • Compounds are pure substances that contain two or more elements mixed together in fixed or definite proportions. • Therefore, we know that the mass of reactants must equal the mass of the products in every chemical reaction.

3. Dalton’s Atomic Theory • Dalton found that the particle theory could not explain why the properties of a compound are different then the properties of the element that make it up. • The particle theory could not explain how particles of different substances could combine or decompose to form new ones.

4. Then came Dalton’s theory: • All matter is made up of sm.particles clld atoms. • Atoms can’t be created or destroyed or split • All atoms of the same element are the same size and weight • Atoms of different elements differ in size and weight • Compounds are created when atoms of different elements link together in definite proportions Eg. Water and peroxide both contain H and O2 but in different proportion. Water is 11%H and 89% O2 whereas peroxide is 6% H and 94% O2

5. The Scientific Process Revised Hypothesis

6. Laws, Theories, Models and Observations • Law- describes and summarizes what always happens. • Theory – a creative way to describe why something happens. • Observation- Scientists observe how matter behaves and reacts during experiments. • Many observations and experiments are needed before a hypothesis can become an accepted theory. • Model – helps to picture structures or processes that cannot be directly seen.

7. Classifying Elements • As elements were discovered, they were given names. The scientist who first discovered an element had the right to name it. • Over time there were many elements with very long names • So, a system of element symbols was developed. • The symbol system is universal which means the same chemical symbols are used by scientists throughout the world • As more and more elements were discovered, Scientists needed a way to classify the elements and organize their observations. • Thus the invention of the periodic table by Dmitri Mendeleev. • The periodic table invented my Mendeleev is still used today with a few modifications.

8. Ways of Classifying Elements

10. Groups of Elements • Alkali Metals • Highly reactive (Boom!) • Has one unpaired electron • Givesup the unpaired electron • Alkaline Metals (Earth metals) • Can react vigorously but not as reactive as the Alkali metals • Noble Gases • Unreactive or inert gases • All the electrons here have “dates” • Halogens • Highly reactive • Have unpaired electrons • Takes an electron • Corrosive • There are other groups and families but were are only covering these.

12. A couple things: • Sci 926 will be changing. Check to make sure my name is in the assignment before you complete it. • There will be a quiz at the end of Sci 926 on the periodic table and symbols!