Unit 3 Notes – Chapter 3 Chemistry 2010-2011 Mr. 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 Table Metals are on the left side of the chart.

Metals Are usually: Lustrous Malleable Ductile good conductors of heat and electricity Tend to lose electrons in chem rxns

Periodic Table Nonmetals 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 Table Metalloids 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.