Chapter 6 – Periodic Table

Development of the Periodic TableIn 1829

Dobereiner’s Law of Triads: The middle element in the triad (group of 3 elements) had atomic weight that was the average of the other two members

Ca Sr Ba (40 + 137) ÷ 2 = 88 40 88 137

Li Na K Cl Br I 7 23 39 35 80 127

Law of Octaves

John Newlands’ Law of Octaves: When elements are arranged in increasing atomic mass the 1st & 8th elements exhibit similar behavior. This behavior repeats in a periodic fashion

In 1863

Little attention was paid to Newlands work because he linked his finding to music.

Dmitri Mendeleev & Lothar Meyer

“I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.” --Mendeleev, Principles of Chemistry, 1905, Vol. II

Mendeleev's periodic table was arranged with increasing atomic weight and attention to chemical properties.

Periodic Table contained columns (groups) & rows (periods).

Mendeleev left gaps in the table. He predicted the discovery of new elements that would fill these gaps.

eka-aluminum, eka-boron, and eka-silicon Gallium, Scandium and Germanium

Later in 1869 German Chemist Lothar Meyer independently published a nearly identical table

In 1906, Mendeleev came within one vote of receiving the Nobel Prize in chemistry

In 1869 & 1871

In 1914 Moseley's Periodic Law • It starts with Rutherford's landmark Gold Foil Experiment

discovering the proton in 1911

• Henry Moseley was able to derive the relationship between x-ray frequency and number of protons.

• Moseley Periodic Law arranges the elements according to increasing atomic numbers and not atomic masses.– some of the inconsistencies associated with

Mendeleev's table were eliminated.

• The modern periodic table is based on Moseley's Periodic Law (atomic numbers).

• At age 28, Moseley was killed in action during World War I

The last major change• Glenn Seaborg discovered the Inner transition metals

(transuranium elements) 94 to 102. • This reconfigured the periodic table by placing the

lanthanide/actinide series at the bottom of the table. • In 1951 Seaborg was awarded the Nobel Prize in

chemistry and element 106 was later named Seaborgium (Sg) in his honor.

In 1940

Groups by NUMBERSIUPAC 1 2 13 14 15 16 17 18

American 1A 2A 3A 4A 5A 6A 7A 8A

European IA IIA IIIB IVB VB VIB VIIB VIIIB

3 4 5 6 7 8 9 10 11 12 3B 4B 5B 6B 7B ----8B----- 1B 2B

IIIA IVA VA VIA VIIA -------VIIIA------ IB IIB

Group or Family – Vertical columns on the PT – Elements in a groups have similar properties

Period – Horizontal rows on the PT

Metals

Most elements are metals. Found to the LEFT of the Zigzag LinePhysical Properties of Metals:• Luster (shininess) • Good conductors of heat and electricity • High density (heavy for their size) • High melting point • Ductile (drawn out into thin wires) • Malleable (hammered into thin sheets)

Chemical Properties of Metals: Easily lose electrons (form positive ions-CATIONS) Corrode easily

NonmetalsNonmetals are found to the

RIGHT of the Zigzag Line Characteristics are opposite

those of metals.Physical Properties of Nonmetals:

– Poor conductor of heat and electricity

– No luster (dull appearance) – Brittle (breaks easily) – Not ductile – Not malleable – Low density – Low melting point

Chemical Properties of Nonmetals:Tend to gain electrons (form

negative ions-ANIONS)

Metalloids• Elements on both sides of the

Zigzag Line • have properties of both metals

and nonmetals. • Physical Properties of Metalloids:– Solids – Can be shiny or dull – Ductile – Malleable – Conduct heat and electricity

better than nonmetals but not as well as metals

• Electron Shielding- the reduction of the attractive force of the nucleus for the outer electrons– caused by electrons in energy

levels between the nucleus and the outer electrons

• Effective Nuclear charge- the charge felt by the valence electrons after taking into account shielding.

Atomic RadiusSince a cloud’s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms.

Atomic radii are usually measured in picometers (pm) or angstroms (Å). An angstrom is 1 x 10-10 m.

Atomic Radius Trend• DOWN A GROUP = Atoms get larger

– Higher energy levels have larger orbitals

– Electron Shielding - core e- block the attraction between the nucleus and the valence e-

• ACROSS A PERIOD Left to Right = Atoms get smaller– Increased nuclear charge without additional shielding pulls e- in

tighter• Nuclear charge is the positive nuclear charge felt by the outer shell

elecrons.

• The trend across a horizontal period is less obvious.• What happens to atomic structure as we step from left to

right?• Each step adds a proton and an electron (and 1 or 2

neutrons).• Electrons are added to existing PELs or sublevels. The effect is

that the more positive nucleus has a greater pull on the electron cloud.

• The nucleus is more positive and the electron cloud is more negative.

• The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period

Ionization Energy

Ionic Radius