Trends in the Periodic Chart …position electrons physical and chemical properties…

transcript

Trends in the Periodic Chart

…position electronsphysical 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

• 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

Periodic trends

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

How many valence electrons?

Simple

Electron configurations

EC ends in…

ns2(n-2)f14(n-1)d?

*ns2(n-1)d?

ns2(n-2)f?

EC ends in…

ns2np?

ns2(n-1)d10np?

ns2 (n-2)f14 (n-1)d10np?

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

What is the charge on the ion?

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

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

• 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

• Atomic size

• INCREASES as you go down

and left

• 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?

Pop Quiz

• Who’s your favorite pop star?

• Which has the greatest / least: Size, IE, EA, e-neg?

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!

The metal/nonmetal line

Diagonal effect!

(probably electron affinity)

Hard (cont’d)

Ionic radius

Negative ions are (way) larger than their atom

Positive ions are (way) smaller than their atom

• Which has the largest / smallest ion?

• Which has the smallest / largest ion?

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

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

Electron Affinity*, Electronegativity*, Ionization energy

Atomic number, shielding, diagonal effect

Reactivity

Melting point?

State!

Know these oxides

Acidic

AmphotericAmphoteric

Trends in the Periodic Chart …position electrons physical and chemical properties…

Documents