Chapter 5 The Periodic Table

Mendeleev’s Periodic Table His strategy for organizing the elements was modeled on a card game. Key Point: Mendeleev arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column. Within a column mass increases from top to bottom

Why did Mendeleev leave spaces? A periodic table is an arrangement of elements in columns based on a set of properties that repeat from row to row. Why did Mendeleev leave spaces? Because many elements had not been discovered. Key Point: The close match between Mendeleev’s predictions of new elements showed how useful his periodic table could be.

The Periodic Law Key Point: Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups.

Periodic Law Periods Groups Each row is a period Runs Number of elements per row varies Energy level = row As you move left to right, atomic # increases Groups Each column Runs Elements within a group have similar properties Ex. Na and K

Periodic law: the pattern of repeating properties 4 pieces of information shown in Fig. 7 Atomic number Element Symbol Element Name Atomic Mass Atomic Mass: is a value that depends on the distribution of elements isotopes and the masses of those isotopes.

Classes of Elements Metals The majority of elements on the periodic table Good conductors of electric current and heat Most are solids at room temperature Malleable and ductile Left side of dark line

Nonmetals Poor conductors of heat and electric current Low boiling points Gases at room temperature Tend to be brittle Extremely reactive Right side of dark line

Metalloids Properties fall between metals and nonmetals On the dark line completely Across a period from left to right the elements become less metallic and more nonmetallic in their properties.

5.3 Groups Valence electrons: is an electron that is in the highest occupied energy level of an atom. It is equal to their group number! These electrons play a role in chemical reactions. Key Point: Elements in a group have similar properties because they have the same number of valence electrons.

Alkali Metal Alkaline Earth Metals Group 1A A single valence electron Very Reactive Alkaline Earth Metals Group 2A 2 valence electrons Harder and higher melting point than 1A

Boron Family Carbon Family Nitrogen Family Group 3A 3 valence electrons Al is the most abundant in the Earth’s crust Carbon Family Group 4A 4 valence electrons 1 nonmetal, 2 metalloids, 2 nonmetals Nitrogen Family Group 5A 5 valence electrons 2 nonmetals, 2 metalloids, 1 metal

Halogens Noble Gases Group 7A 7 valence electrons A range of physical properties Noble Gases Group 8A All but He, have 8 valence electrons, He has 2 valence electrons Colorless, odorless and extremely unreactive

Tell the number of valence electrons for the following: Na F I Al C Pb Ba