the periodic table. objective you will be able to discuss the contributions of mendeleev, moseley,...
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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