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