trends in the periodic chart
DESCRIPTION
Trends in the Periodic Chart. …position electrons physical and chemical properties…. …the position indicates physical and chemical properties of elements!. There are two effects:. Attraction— Shielding—. There are two effects:. Attraction— as Z increases, attraction increases BUT - PowerPoint PPT PresentationTRANSCRIPT
There are two effects:
• Attraction— as Z increases, attraction increases
BUT
• Shielding— as Z increases, shielding increases:
--a little bit with each electron in the same period
--in a great jump as you start the next period
Shielding
• Shielding is the weakening of attraction due to electrons interfering with the attraction of the nucleus
• Shielding increases a little as you go across a period (not as much as attraction)
• Shielding jumps tremendously as you start a new energy level
Simple
Valence electrons
– The representative (tall) columns represent the number of valence electrons
– Transition elements have only two valence electrons, but have a part-filled d sublevel
Simple
Ionization pattern
• Metals have
-only a few valence electrons
-lose these electrons to empty their valence level
-form positive ions
Simple
Ionization pattern
• Non-metals have
-more valence electrons
-gain electrons to fill valence level
-form negative ions
Medium
Atomic size
• In a column, a lower row indicates an extra energy level
• Outer energy levels are larger (due to shielding)
• The largest atom in a column is the bottom element
Medium
• Ionization energy— the energy required to remove an electron
X + IE X+ + e-
• Outer energy levels are farther from the nucleus
• It is easier to remove an electron from a larger energy level
• The lowest ionization energy is at the bottom of the column
Medium
Electronegativity
—the attraction an atom has for a shared pair of electrons
• See previous—the highest electronegativity is at the top
Medium
Electron affinity
—the attraction an atom has for an electron from outside
X + e- X- + EA
• See previous—the highest electron affinity is at the top
One moment…
As you go across a row, you get more protons in the nucleus
• They attract the electrons better
• Each energy level gets smaller
Hard
• Atoms get smaller as you go across a row• Ionization energy gets larger• Electronegativity gets larger• Electron affinity gets larger
--All because there are more protons—Z increases faster than shielding in a
period
Recap
• Electronegativity, ionization energy, and electron affinity
• INCREASE as you go up
and right
Pop Quiz
• Which element on the entire periodic chart is the largest?
• Smallest?
• Which element on the entire periodic chart has the largest IE?
• Smallest?
Pop Quiz
• Which element on the entire periodic chart has the largest e-negativity?
• Smallest?
• Which element on the entire periodic chart has the largest EA?
• Smallest?
The diagonal effect
• Of the previous four elements, the ones in the same row and column are easy, right?
• What can you say about carbon and iodine?
• Try this– they might be just about the same!
Hard (cont’d)
Ionic radius
Negative ions are (way) larger than their atom
Positive ions are (way) smaller than their atom
Hard (cont’d)
Second and third ionizations
• If you ionize an atom, you make a (+) ion
• It’s harder to ionize it again
• It gets way harder after you empty the valence level
Hard (cont’d)
Second and third ionizations
• If you ionize an atom, you make a (+) ion
• It’s harder to ionize it again
• It gets way harder after you empty the valence level
Why?
Hard (cont’d)
• First, second, and third ionization energies
X + IEX+1 + e-
X+1 + IE2X+2 + e-
X+2 + IE3X+3 + e-
Disclaimers
• Noble gasses have no electronegativity—they don’t share electrons
• Noble gasses have no electron affinity—they don’t gain electrons
• Most metals have no electron affinity—they don’t gain electrons
Ionization Energies in kJ/mol• 1 2 3 4 5H 1312He 23725250Li 520 7297 11810Be 899 1757 14845 21000B 800 2426 3659 25020 32820C 1086 2352 4619 6221 37820N 1402 2855 4576 7473 9442O 1314 3388 5296 7467 10987F 1680 3375 6045 8408 11020Ne 2080 3963 6130 9361 12180Na 496 4563 6913 9541 13350Mg 737 1450 7731 10545 13627
Ionization Energies in kJ/mol• 1 2 3 4 5H 1312He 23725250Li 520 7297 11810Be 899 1757 14845 21000B 800 2426 3659 25020 32820C 1086 2352 4619 6221 37820N 1402 2855 4576 7473 9442O 1314 3388 5296 7467 10987F 1680 3375 6045 8408 11020Ne 2080 3963 6130 9361 12180Na 496 4563 6913 9541 13350Mg 737 1450 7731 10545 13627