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Unit 3 Notes – Chapter 3
Chemistry2010-2011Mr. Nelson
Mendeleev
Dmitri Mendeleev first organized elements according to atomic mass.
He noticed similarities in their chemical properties appeared at regular intervals Such a pattern is called periodic Thing to remember: its just a general
trend
Mendeleev’s first table
Periodic Law Mendeleev’s table has gaps!
Two questions he posed:
1. Why could most elements be arranged in order of increasing atomic mass, but some couldn’t?
2. What is the reason for chemical periodicity?
Periodic Law Moseley, who worked with Rutherford,
discovered that atomic number, not atomic mass, is the basis of organization. This led to…
Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.
Periodic Table Organization
Vertical columns in the periodic table are known as groups or families
Periodic Table Organization
Horizontal Rows in the periodic table are known as Periods
Valence Electrons Outer-most electrons
Periodic TableMetals are on the left side of the chart.
MetalsAre usually:
Lustrous Malleable Ductile good conductors of
heat and electricity Tend to lose
electrons in chem rxns
Periodic TableNonmetals are on the right side of the periodic table (with the exception of H).
Nonmetals
Are usually Dull brittle poor conductors of
heat and electricity. Tend to gain
electrons in chem rxns.
Periodic TableMetalloids border the stair-step line (with the exception of Al, Po, and At).
Metalloids Have some
characteristics of metals and nonmetals.
For Example: Silicon looks shiny,
but is brittle and fairly poor conductor.
Alkali Metals: Group 1
Soft! Can be cut like butter with a knife
React with O2 in air
Reacts VIGOROUSLY with water
Alkaline-earth Metals Group 2
Harder, denser, higher melting points than group 1.
Reactive, but not like group 1.
Reacts with oxygen in air, like group 1.
Transition elements Groups 3-12
They are all metals
Harder, denser, with higher melting points (except for mercury)
Lanthanides: elements 57-71 Shiny, reactive metals
Actinides: elements 89-103 All have radioactive forms
Main block elements: groups 13-16 Named by the uppermost element
Halogens: Group 17 Reactive, all are nonmetals.
Noble Gases Group 18
Escaped detection for some time due to their nonreactivity
Hydrogen Group all on its own.
Electron dot diagram Represent valence electrons 1 dot = 1 electron Example: Rubidium
Diatomic Molecules
These seven elements occur naturally as molecules containing two atoms.