The Periodic Table

History, Organization and Trends

Lavoisier, Dobereiner, & Newlands

1790- Lavoisier, 23 elements

1870- Dobereiner, triads, 70 elements

1864- John Newlands, Law of Octaves

Dimitri Mendeleev (1834-1907) A Russian chemist who in 1869

published an organized scheme for the elements called the Periodic Table. The elements were arranged in ascending order of atomic mass and also by properties. He was able to predict the properties of undiscovered elements because of their placement in the periodic table. (gallium, scandium, germanium)

1875 1886

Henry Mosely (1887-1915)

Henry Moseley rearranged the elements in 1913 by ascending order of atomic number.

The Modern Periodic Table

Periodicity- the tendency to recur at regular intervals

  Periodic Law: The properties of the

elements repeat periodically when the elements are arranged in increasing order by their atomic numbers.

 

Modern PT Organization Groups/ families -vertical columns (similar

properites) Periods- horizontal rows Representative elements- Group “A” Transition elements- Group “B” Metals- LEFT Nonmetals- RIGHT Metalloids- On LINE

Groups of elements Metals

Alkali Alkaline Earth Transition Inner transition

Nonmetals Halogens Noble gases

Hydrogen is a nonmetal

Properties of Metals Solid High melting point Shiny, luster Good conductors of heat and electricity Malleable Ductile Few valence electrons Reacts by giving up electrons

Main group metals are highly predictable, transition metals are not.

Alkali metals - group 1, 1 valence electron, highly reactive so not found free in nature, reacts with water to give off hydrogen gas, very soft

Alkali earth metals – group 2, 2 valence electrons, reactive and not found free in nature, reacts some with water, fairly hard

Transition metals – valence electrons vary, some are unreactive to water, some are found free in nature

Lanthanide series – also called the rare earth elements, part of the inner transition elements, unpredictable, natural abundance on Earth is less

than 0.01% Actinide series – part of the inner transition elements, all are

radioactive, unpredictable

Properties of Nonmetals

Brittle if solid, many are gases

Dull

Poor conductor of heat, does not conduct electricity

Seven diatomic gases-H2, N2, O2, F2, Cl2, Br2, I2

3-8 valence electrons

Reacts by taking electrons from other atoms

More reactive nonmetals are at top of group

Halogens- group 17, 7 valence electrons, reacts by taking electrons from other atoms

Noble gases- group 18, 8 valence electrons, inert gases, monatomic gases, most do not react with other elements

* Hydrogen is considered a nonmetal

Metalloids

Has properties of metals and nonmetals

Semiconductors

Valence Electrons

Group “A” number tells valence electrons

6.3 Trends

Atomic Radius

How Big is the atom? Group Trend – decreases left to right Period trend- increases top to bottom

Ionic Radius

How big is the ion? Group trend- Increases top to bottom

(note metalloid line) Period trend – decreases to metalloid

line, jumps up, then decreases again

Ion- an atom or a bonded group of atoms that has a positive or negative charge

Ionization Energy How hard is it to remove 1 electron?

Group Trend- decreases top to bottom Period Trend- increases left to right

Octet rule- atoms gain, lose or share electrons to acquire a full set of valence electrons

Electronegativity

How hard does the atom pull on shared electrons? Group Trend- Decreases top to bottom Period Trend- Increases left to right