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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