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In Class Discussion Monday April 7,2014

In Class Discussion Monday April 7,2014. Chapter 10. The Periodic Law. Chapter 10 Outline. Elements and compounds Chemical change Three classes of matter The atomic theory The periodic law Construction and meaning of the periodic table of the elements Atomic structure

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In Class Discussion Monday April 7,2014

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  1. In Class DiscussionMonday April 7,2014

  2. Chapter 10 The Periodic Law

  3. Chapter 10 Outline • Elements and compounds • Chemical change • Three classes of matter • The atomic theory • The periodic law • Construction and meaning of the periodic table of the elements • Atomic structure • Shells and subshells • Atomic structure explains the periodic table • Chemical bonds • Types of chemical bonds • Naming chemicals • Chemical equations

  4. To Start: A History Lesson In the beginning, all “chemists” were “alchemists” • Chemistry began with a search for a way to change ordinary metals into GOLD!! • Did it work?? NO!

  5. TWO BASIC TYPES OF ALTERATIONS • PHYSICAL CHANGE • Usually involves the REARRANGMENT of atoms or molecules • Examples: melting, freezing, etc. • CHEMICAL CHANGE • Alterations to the atoms or molecules themselves • Examples: loss or gain of an electron • This happens whenever a CHEMICAL BOND is formed or destroyed.

  6. Combining Elements • When two elements form a chemical bond, a substance with properties different than those of the two starting elements is formed • EXAMPLE • SODIUM • CHLORINE • When chemically bonded, they form SODIUM CHLORIDE • The physical and chemical properties of sodium chloride are DIFFERENT from either sodium or chlorine!

  7. The Work of the Alchemists • Alchemists could not turn ordinary elements to gold but their work led to the idea of ELEMENTS • Substances that could NOT be “broken down” into any other substance. • If there were only a limited number of ELEMENTS, then all the variations in matter that we see must be some combination of these … A VERY PROFOUND IDEA!

  8. Three Classes of Matter • Element • A substance that cannot be broken down into a simpler substance • Compounds • Two or more elements combined CHEMICALLY • Mixtures • A substance with a variable composition. It can be broken down by PHYSICAL means

  9. You Should Already Know… • The difference between ATOMS and MOLECULES • An “atom” is a particular element • There are a limited number • See the periodic table • A MOLECULE is a combination of two or more atoms • The atoms may be the same (O2) • Or different (H2O)

  10. Elements • The smallest piece of matter that retains the CHEMICAL PROPERTIES of the matter • There are over 100 elements identified • Most occur as solids • The most prevalent element in the universe is the simplest atom: HYDROGEN • On Earth, 96% of earth’s mass is comprised of only 4 elements: oxygen, silicon, iron and magnesium • In the human body: oxygen is the most abundant, carbon, hydrogen, nitrogen, calcium and phosphorus.

  11. Classifying Matter • Compounds: chemical combinations of two or more elements (zinc sulfide, water) • Mixtures: combinations of elements • Heterogeneous mixture: A substance whose properties vary from one particle to the next (a mixture of zinc powder and sulfur powder without heating them) • Homogeneous mixture: components are mixed so that the mixture is uniform throughout (sea water)

  12. Powder of Zinc and Sulfur Heat + = Zinc Powder Zinc Sulfide Sulfur Powder

  13. Classification of Matter

  14. The Differences: Compound/Solution • Tests for determining whether two elements have combined chemically or simply mixed • Determine if boiling or freezing can separate the constituents. The change of state (solid, liquid, gas) occur at specific temperatures for elements and compounds but not for mixtures • Check the relative masses in different samples of the material. • The elements in a given compound are always present in exactly the same proportions. The mass ratio of the nitrogen and oxygen in air is 3.2:1=32:10 This mass ratio in nitric oxide is exactly 88:100

  15. Nitric Oxide compound • BUT

  16. Law of Definite Proportions • In a chemical compound, the proportions of each constituent element is fixed THE ELEMENTS THAT MAKE UP A COMPOUND ARE ALWAYS COMBINED IN THE SAME PROPORTIONS ACCORDING TO THEIR MASS

  17. Example: Water The law of definite proportions says in a water molecule, there are always TWO hydrogen atoms, and ONE oxygen atom… 36.04g           36.04g

  18. Building Blocks of Matter • The Ancient Greeks had a simple understanding of nature • They thought that EVERYTHING was made from only FOUR fundamental “ELEMENTS” Earth Wind Fire Water These were considered to be “basic particles” • Then John Dalton (1766-1844) proposed that the basic particles were atoms

  19. Dalton’s Idea • Dalton proposed that all atoms of each element were exactly the same, and that all other atoms were different • Dalton discovered the relative masses of the atoms of the elements known at the time • He was the first to understand that a chemical reaction was really a rearrangement of atoms, not the creation or destruction of atoms

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