The periodic table arranges elements in order of increasing atomic number, with each row representing a period and each column a group or family. Periodic law states that physical and chemical properties repeat periodically when elements are arranged this way. Properties vary systematically across periods, with elements becoming less metallic and more nonmetallic from left to right, ranging from the most reactive metal to the most reactive nonmetal.

1. The Modern Periodic Table Periodic Law Atomic Mass Classes of Elements Variation Across a Period

2. Periodic Law The modern periodic table, elements are arranged in increasing atomic number (Number of protons) Each row is called a Period Each column is called a Group or Family

3. Periodic Law Periodic Law = Properties of elements that are repeated in predictable ways when arranged into groups

4. Periods / Group Family Period

5. Atomic Mass Is the weighted average of the masses of an element. Which includes all Isotopes One-twelfth the mass of carbon-12 is used to define an atomic mass unit or amu .

6. Classes of Elements Metals Good conductor of electricity & heat—ductile--malleable Nonmetals Poor conductors of E&H—low b.p.( gas at room temp)—brittle if solid at r.t.—some very reactive Metalloids Have properties of both metal and nonmetal…

7. Variation Across a Period Across a period from left  right Properties of Elements become less metal and more nonmetal . Most reactive metal Most reactive nonmetal