Decoding the Periodic Table Part 2 CHAPTER 12 Decoding the Periodic Table Part 2

First Periodic Table The first periodic table was devised by Dmitri Mendeleev and published in 1869, with 63 elements

Periodic Table —118 elements

Organization of the Periodic Table 18 columns (groups or families) 7 horizontal rows (periods)

Three Classes of Elements Metals (gold) Nonmetals (sulfur) Metalloids (germanium)

Three Classes of Elements

Moving from left to right As you move from left to right across a row, the elements become less metallic!

Groups Elements in the same group have often have similar chemical and physical properties (also called “family”)

Grouping the Elements Elements in a group have similar properties because they have the same number of electrons in the outer level (valence electrons) Atoms give/take/share electrons with other atoms to have a complete set of electrons in their outer level Elements that undergo such processes are called reactive and can combine to form compounds

Hydrogen Very reactive Located above group 1 because it also has 1 electron in the outer level Hydrogen’s physical properties are more like those of non-metals The most abundant element in the universe

Group 1: Alkaline Metals Very reactive 1 electron in outer level Softness, color of silver, shiny, low density

Group 2: Alkaline Earth Metals Very reactive, but less so than group 1 2 electrons in the outer level Color of silver, higher densities than alkali metals

Groups 3-12: Transition Metals Less reactive than alkaline earth metals 1 or 2 electrons in the outer level Good conductors, shiny, higher densities and melting points than groups 1 and 2

Groups 13-16 Named for the first element in the group (i.e. boron, carbon…) 3, 4, 5 and 6 electrons in the outer shell respectively Reactivity varies, but tend to be reactive

Group 17: Halogens Very reactive 7 electrons in the outer level Non-metals When halogens combine with metals they form salts

Group 18: Noble Gases Unreactive (very stable) 8 electrons in the outer level (with the exception of helium which has 2) Colorless, odorless gases at room temp