Chapter 5 The Periodic Table

Mendeleev’s Periodic Table 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, masses increased from top to bottom. Periodic table: an arrangement of elements in columns, based on a set of properties that repeat from row to row.

The Periodic Law Mendeleev developed his periodic table before the discovery of protons. In the modern period table, elements are arranged by increasing atomic number (number of protons). Periodic law: the pattern of repeating properties displayed by elements in the periodic table.

Periods and Groups Periods: horizontal rows. Groups: vertical columns. Members of a group in the periodic table have similar chemical properties. See Figure 6, page 131. See element example, page 133. See Figure 8, page 134.

Atomic Mass Atomic mass is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes. In nature, most elements exist as a mixture of two or more isotopes. Atomic mass unit (amu): one twelfth of the mass of a carbon-12 atom.

Classes of Elements Elements are classified as metals, nonmetals, and metalloids. Metals: located on the left. Nonmetals: located on the right. Metalloids: located in-between.

Metals (1) The majority of elements in the periodic table are classified as metals. Metals: elements that are good conductors of electric current and heat. Metals are solid at room temperature (exception: mercury)

Metals (2) Most metals are malleable and ductile. Malleable: capable of being hammered into a thin sheet. Ductile: capable of being drawn into a thin wire.

Metals (3) Metals in groups 3-12 are called transition metals. Transition metals: elements that form a bridge between the elements on the left and right sides of the periodic table. Examples: copper, silver

Nonmetals Nonmetals: elements that are poor conductors of heat and electric current. Many nonmetals are gases at room temperature. All the gases in the periodic table are nonmetals. Those nonmetals that are solid at room temperature tend to be brittle.

Metalloids Metalloids: elements with properties that fall between those of metals and nonmetals. A metalloid’s ability to conduct electric current varies with temperature.

Valence Electrons The number of an A group matches the number of valence electrons in an electron configuration for an element in that group. Valence electron: an electron that is in the highest occupied energy level of an atom. Valence electrons play a key role in chemical reactions. Elements in a group have similar properties because they have the same number of valence electrons.

1A  Alkali Metals These metals have 1 valence electron and are extremely reactive. The reactivity of alkali metals increases from the top of Group 1A to the bottom. Sodium: Na Potassium: K

2A  Alkaline Earth Metals All alkaline earth metals have 2 valence electrons. Metals in Group 2A are harder than metals in Group 1A. Magnesium: Mg Calcium: Ca

3A  The Boron Family All elements in Group 3A have 3 valence electrons. Boron: B Aluminum: Al Aluminum is the most abundant metal in Earth’s crust.

4A  The Carbon Family All elements in Group 4A have 4 valence electrons. Carbon: C Except for water, most of the compounds in your body contain carbon. Silicon: Si Silicon is the second most abundant element in the Earth’s crust.

5A  The Nitrogen Family All elements in Group 5A have 5 valence electrons. Nitrogen: N Phosphorus: P Nitrogen and phosphorus are important elements in fertilizers.

6A  The Oxygen Family All elements in Group 6A have 6 valence electrons. Oxygen: O Oxygen is the most abundant element in Earth’s crust. Sulfur: S The main use of sulfur is the production of sulfuric acid—more sulfuric acid in produced in the U.S. than any other chemical (fertilizers).

7A  The Halogens All elements in Group 7A have 7 valence electrons. Halogens are highly reactive nonmetals. Most reactive: fluorine Second-most reactive: chlorine Fluorine: F Chlorine: Cl Bromine: Br Iodine: I

8A  The Noble Gases All elements in Group 8A have 8 valence electrons—except for helium, which has 2. The noble gases are colorless and odorless and extremely unreactive. Helium: He Neon: Ne Argon: Ar