The Periodic Table Unit 6

Why is the Periodic Table important to me?

• The periodic table is the most useful tool to a chemist.

• You get to use it on every test.

• It organizes lots of information about all the known elements.

Pre-Periodic Table Chemistry …

• …was a mess!!! • There were at least 55

elements discovered • No organization of

elements. • Varying properties

amongst the elements, but some similar trends

• Difficult to find information.

Dmitri Mendeleev

1834 - 1907

In 1869 he published a table of the elements organized by increasing atomic mass.

Mendeleev’s Periodic Table

• Mendeleev looked at all known elements and began to arrange them

• Studied – Number of valence electrons – Similar chemical and physical properties – Atomic weight

• Arranged elements in horizontal rows (periods) and columns (groups or families)

• Left holes where discovered elements did not fit

Dmitri Mendeleev: Father of the Table

HOW HIS WORKED… • Put elements in rows by

increasing atomic weight. • Put elements in columns

by the way they reacted.

• stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U)

• was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.

After the discovery of Sc, Ga, and Ge between 1874 and 1885, and the fact that Mendeleev’s predictions for their properties were amazingly close to the actual values, his table was generally accepted.

Henry Moseley

1887 - 1915

In 1913, through his work with X-rays, he determined the actual atomic number of the elements. He rearranged the elements in order of increasing atomic number (number of protons).

His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting by a sniper’s bullet, at the age of 28.

Memory trick: Mos Pros

Modern Periodic Table = atomic number

Periodic Table Geography

The horizontal rows of the periodic table are called PERIODS.

The vertical columns of the periodic table are called GROUPS, or FAMILIES.

Atoms in the same group have similar chemical

properties because they have the same number of VALENCE ELECTRONS!

Metals to the left of the zig zag line

Nonmetals to the right of the zig zag line

Characteristics of Elements

• Metals – Shiny when smooth

and clean – Solid at room temp. – Good conductors of

heat and electricity – Malleable – Ductile

Nonmetals – Generally gases or

brittle, dull-looking solids

– Poor conductors of heat and electricity

•Metalloids

– Have physical and chemical properties of both metals and nonmetals!

Group Numbering 1 2 13 14 15 16 17 18

3A 4A 5A 6A 7A 8A

Electronegativity

• The ability of an element’s atoms to attract electrons in a chemical bond

Generally Increasing

Gen

eral

ly D

ecre

ases

Electronegativity

• Most electronegative element is Fluorine (might want to make a note of that)

• Let’s Practice - Between the elements As, Sn and Sb, which is

the most electronegative? • As

– Between the elements Sr, Ba and Ra, which is the most electronegative?

• Sr

Ionization Energy

• The energy needed to remove an electron from a gaseous atom

Generally Increasing

Gen

eral

ly D

ecre

ases

Ionization Energy

• Fluorine has the highest ionization energy of all the elements (might want to make a note)

• Let’s Practice – Between Na, Mg, K and Ca, which has the

highest ionization energy? • Mg

– Between Pd, Ag and Cd, which has the highest ionization energy?

• Cd

Atomic Radii

• Half the distance between the nuclei of adjacent, identical atoms in crystals or molecules Generally Decreases

Gen

eral

ly In

crea

ses

Atomic Radii

• Francium has the largest atomic radius (make a note!)

• Let’s practice – Of Li, Be, Na and Mg, which has the largest

atomic radius? • Na

– Of S, Se, Te and Po, which has the largest atomic radius?

• Po