Transcript The Periodic Table

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 Table
Dmitri Mendeleev (1869):
published first periodic table.
Mendeleev’s
Periodic Table
• arranged by increasing
atomic mass
• grouped by similar
properties
• predicted the
existence and properties
of unknown elements
(Ga, Ge, Hf)
Mendeleev’s
Predictions
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.
Mendeleev’s
Question
Is the atomic mass
of Tellurium (Te)
incorrect?
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 Table
Glenn 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 properties
of the elements
repeat 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 Trends
group trend (down a column): radius increases
because 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” electrons
because they are large (low electronegativity).
Non-metals tend to attract electrons because
they are small (high electronegativity).
Reactivity Trends
same group = similar properties (like reactivity) = similar
e- 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