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Section 3.4. Elements and Compounds. Objectives. Distinguish between elements and compounds Describe the organization of elements on the periodic table Explain how all compounds obey the laws of definite and multiple proportions. Composition of Matter. Elements.
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Section 3.4 Elements and Compounds
Objectives • Distinguish between elements and compounds • Describe the organization of elements on the periodic table • Explain how all compounds obey the laws of definite and multiple proportions
Elements • Building blocks of matter • Cannot be separated into simpler substances • 91 elements occur naturally on Earth • 118 total known elements
HOW HIS WORKED… rows by increasing atomic weight. columns by reactivity SOME PROBLEMS… blank spaces for undiscovered elements. Favored reactivity over atomic weight Dmitri Mendeleev
Rows or Periods • Now rows are by increasing ATOMIC NUMBER!! • Periods (1 to 7).
Columns/Groups/Families • Groups 1 to 18. • Elements in the same group have similar chemical and physical properties!! • share common traits= families
Compounds • Two or more elements chemically combined • 10 million known compounds • Table salt, aspirin, water
Law of Definite Proportions • A compound is always composed of the same elements in the same proportion by mass
Percent by Mass Percent by mass (%) = mass of element x 100 mass of compound
Law of Multiple Proportions • When different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers
Homework • Classification Worksheet • Laws Worksheet