Chapter 6 notes

The Periodic Table

Dobereiner – attempted to classify the elements in 1817.

Triad – three elements with similar propertiesThe middle element has an atomic mass about halfway between the other two.

Newlands in 1863 arranged the elements in order of increasing atomic masses

Appeared to be a repetition every eighth element

7 elements into 7 groups Law of Octaves

Mendeleev – properties of elements were a function of atomic masses

Left blank spots

Correctly predicted properties and masses of unknown elements

Mendeleev, the “Father of the periodic table”

Moseley– Found atomic number and problem solved!!!

Periodic Law – properties of the elements are a periodic function of their atomic numbers

Periodic table from 1930

This is how our table is organized today

Periodic Table

• Groups or families are columns that have elements with the same number of valence electrons

• Periods or series are rows on the chart. The properties vary.

• 8 main groups• Transition elements• Rare earth elements

Metals

Tend to Lose electrons

General rule–3 or fewer electrons in the outer levelLeft side of table

Alkali metals group 1

Alkali earth metals group 2

Nonmetals tend to Gain

electrons

5 or more electrons in the outer levelRight on the table

Halogens and Noble gases

Metalloids

Have properties of both metals and nonmetals

Located on ladder like line on table (not Al)

Examples of periodic law

• Metallic vs. nonmetallic character

• Size of atoms

Periodic Table

Each time a new energy level is started, a new row in the table begins

Transition elements – inner building

Columns 3-12

Lanthanoid series

Z = 57 to Z = 70

2 electrons in outer level4f sublevel

Actinoid Series

Z = 89 to Z = 102

5f sublevel

Ionization Energy

• To form a cation (a positively charged ion) an electron must be removed from the atom

• Ionization Energy—the energy needed to remove an electron from a gaseous atom

• A higher ionization energy means that an atom likes to hold onto its valence electrons

Group 1 elements (Li, Na, K, Rb) have low ionization energies, while the noble gases (He, Ne, Ar, Kr, Xe)

have high ionization energies

Ionization Energy• After removing one electron, it is possible

to remove another. This is called second ionization energy.

• Each successive removal of an electron has a higher ionization energy.

Ionization Energy

• Trends:– Within a period: ionization energies generally

increase across a row.– Within a group: ionization energies generally

decrease down the columns.

• Octet Rule: atoms tend to gain, lose, or share electrons to get a full set of 8 electrons

Electronegativity

• Liking for electrons when bonded