3. Objectives: Describe how Mendeleev arranged elements in the first periodic table. Explain how elements are arranged in the modern periodic table. Comparemetals, nonmetals, and metalloids based on their properties and on their location in the periodic table. Describethe difference between a period and a group.
4. Discovering a Pattern In 1869, Russian chemist Dmitri Mendeleev Arranged the elements in order of increasing atomic mass. Periodic Properties of the Elements When the elements are arranged in order of increasing atomic mass Those that had similar properties occurred in a repeating pattern. These repeating patterns are periodic,meaning that they happen at regular intervals.
5. Predicting Properties of Missing Elements Mendeleev’s arrangement had gaps in its pattern. Mendeleev predicted that elements yet to be found would fill these gaps. He also predicted the properties of the missing elements. By 1886, all of the gaps had been filled and Mendeleev’s predictions were right.
6. Changing the Arrangement A few elements’ properties did not fit in the pattern of Mendeleev’s table. In 1914, British scientist Henry Moseley found the number of protons—the atomic number—in an atom. When the elements were arranged by atomic number, they fit the pattern in Mendeleev’s table. Periodic Law: physical and chemical properties of the elements are periodic functions of their atomic numbers.
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8. Classes of Elements Elements are classified as: Metals Nonmetals Metalloids The number of electrons in the outer energy level One characteristic that helps determine which category an element belongs in. The zigzag line on the periodic table Can help you recognize which elements belong in which category.
9. Metals: Found to the left of the zigzag line. Atoms of most metals have few electrons in their outer energy level. All metals are Shiny Ductile Malleable Good conductors of electric current and thermal energy.
10. Nonmetals Found to the right of the zigzag line. Atoms of most nonmetals have an almost complete set of electrons in their outer energy level. Nonmetals are: Not shiny Not ductile, or malleable Poor conductors of electric current and thermal energy.
11. Metalloids The elements that border the zigzag line. Atoms of metalloids have about half of a complete set of electrons in their outer energy level. have some properties of metals and some properties of nonmetals. also called semiconductors
12. Decoding the Periodic Table Each Element is Identified by a Chemical Symbol Each square on the periodic table includes Element’s name Chemical symbol Atomic number Atomic mass. For most elements The chemical symbol has one or two letters. The newest elements have temporary three-letter symbols. Atomic number 6 C12.011 Carbon Chemical Symbol Atomic Mass Element Name
13. Horizontal rows Are Called Periods The chemical and physical properties of elements in a row follow a repeating pattern as you move across the period. Vertical columns Are Called Groups Elements in the same group often have similar chemical and physical properties. Period Group
