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 2

Periodic Table — 118 elements 3

Organization of the Periodic Table 7 horizontal rows (periods) 18 columns (groups or families) 4

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! 7

Groups Elements in the same group have often have similar chemical and physical properties (also called “family”) 8

Grouping the 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 10

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