3.2 lecture 2008

3.2 A Guided Tour of the Periodic Table

Pages 77 - 85

Goal 1

Explain the relationship between the periodic table and the arrangement of electrons

within an atom.

• Order based on number of protons

• Similar elements grouped together

• Similarities then occur in regular pattern

• Helps predict properties

• Horizontal rows are called “periods”

• Can be used to determine electron arrangement

• Works up to element 20, Ca

• Each horizontal row is an energy level

• Each square counts as an electron in that energy level

Li has 3 electrons level 1 = 2e- level 2 = 1 e-

N has 7 electrons Level 1 = __ Level 2 = __

• Each vertical column is a Group

• Elements in a group have similar chemical properties

• Valence electrons 1, 2, 13-18

Goal 2

Explain ion formation

• Purpose of Ionization– Full outermost shell– Gain or lose valence electrons– Results in imbalanced electronic charge

• Loss of electron yields “+” charge– Lose 1 electron 1+ charge– Lose 2 electrons 2+ charge– Lose 3 electrons 3+ charge

• Happens with small # of valence electrons

• Left-side of the periodic table– Which groups???

• What will the charge be on the following ions?– H– Li– Ca– K– W

• Gain of electrons yields “-” charge– Gain 1 electron 1- charge– Gain 2 electrons 2- charge– Gain 3 electrons 3- charge

• Happens with high # of valence electrons

• Which groups???

• What will the charge be on the following ions?– F– Cl– S– P– N

Goal 3

Use the periodic table to determine the number of protons, electrons, and

neutrons

• Atomic number– Protons– Electrons

6 24

carbon12

• Mass number– Protons + neutrons

6 24

carbon12

• Protons = atomic number

• Electrons = atomic number

• Neutrons = mass number – atomic number

Goal 4

Work with isotopes and average atomic mass

• Isotopes– Same number of protons– Different number of neutrons– Chemical properties remain same– Mass number changes– Mass changes

• Example – One atom of “Carbon”

• 6 protons• 6 neutrons• Atomic mass ~ 12

– One isotope atom of “Carbon – 14” • 6 protons• 8 neutrons !!!• Atomic mass ~ 14

• How many neutrons are in the following isotopes?– Nitrogen -15– Sulfur – 35– Calcium – 45– Iodine - 131

• The mass of atoms and isotopes

• Atomic mass unit1.0 amu = one proton = one neutron

• Average atomic mass– Weighted average of isotopes– Nearest whole number indicates most

common isotope6 2

4

carbon12.011