The Periodic Table

Objective

• You will be able to discuss the contributions of Mendeleev, Moseley, and Seaborg in the development of the periodic table.

The Periodic TableDmitri Mendeleev (1869):published first periodic table.

• arranged by increasing atomic mass• grouped by similar properties• predicted the existence and properties of unknown elements (Ga, Ge, Hf)

Mendeleev’s Periodic Table

Mendeleev’sPredictions

Property

Prediction

for

ekasilicon

Actual

for

Ge

Atomic

mass

72

amu

72.59

amu

Density 5.5

g/cm3

5.32

g/cm3

Formula

of oxide

EsO2 GeO2

Formula of

chloride

EsCl4 GeCl4

Predicted in 1871;Ge was discovered in 1886.

Is the atomic mass of Tellurium (Te) incorrect?

Mendeleev’sQuestion

Henry Moseley

Henry Moseley (1911): each element has different # of p+.The table should be arranged by atomic number, not atomic mass.

Moseley was killed in Turkey during WWI.

The Modern TableGlenn Seaborg arranged our modern table (d-block and f-block).

Objectives

• Know the periodic law.• Explain how atomic radius is measured.• Understand, identify, and discuss the trends on

the periodic table for atomic radius and for electronegativity.

Periodic Law

periodic law:the propertiesof the elementsrepeat periodically

“periodicity”

Atomic Radius

It is difficult to measure atomic size (no definite edge).

atomic radius: ½ the distance between the nuclei of two bonded atoms

Atomic Radius Trendsgroup trend (down a column): radius increasesbecause new energy levels

period trend (across a row): radius decreases because electrons are in the same “shell” but added protons pull inward on the shell.

Electronegativity

electronegativity: the tendency of an atom to attract electrons when it is bonded to another atom

The nucleus of a small atom pulls strongly on the outer electrons of a large atom

+ + +

Electronegativity Trends

group trend: electronegativity decreases (atoms get larger)

period trend: electronegativity increases (atoms get smaller)

Objectives

• You will be able to compare the reactivity of elements.

• You will be able to explain why specific elements are either reactive or unreactive.

Metals and Non-Metals

Metals tend to lose their outer “valence” electronsbecause they are large (low electronegativity).

Non-metals tend to attract electrons becausethey are small (high electronegativity).

Reactivity Trendssame group = similar properties (like reactivity) = similare- configurations

metals: largest, with fewest valence e- are most reactive non-metals: smallest, with most valence e- are most reactive (excluding noble gases—outer shell is full)

Which is the most reactive?• Ca, Cu, Rb, Na• S, Cl, Br, C, Ne

Reaction Clips

• Alkali Metal Reactions• Sodium and Chlorine Reaction• Fluorine Reactions