Periodicity.Why is the periodic table this goofy shape?

Why this shape?There is nothing fundamental about this arrangement of elements.

In fact, the f-block even has to get cut out just so the thing will print on a standard piece of paper well.

Some Other ShapesHere are some other arrangements:

In 3D!

Why this shape?All of these try to do the same thing: arrange all the elements in a way that makes for useful patterns.

Mendeleev’s original table was revolutionary, but not terribly useful for many modern things.

So What is Ours Good At?Metals vs non-Metals

Pretty good here.A stepped dividing line is a bit non-optimal.The placement of hydrogen is odd for this.

So What is Ours Good At?Valence electrons

Very good here.

Helium is awkward, but that’s inevitable due to lack of p orbitals.

So What is Ours Good At?Three new things:

1.Atomic radius

2.Ionization Energy

3.Electron Affinity

So What is Ours Good At?Three new things:

1.Atomic radius: where you define the ‘end’ of an atom is a little nebulous, but we can make up an arbitrary choice and get relative sizes that way.

2.Ionization Energy

3.Electron Affinity

So What is Ours Good At?Three new things:

1.Atomic radius: where you define the ‘end’ of an atom is a little nebulous, but we can make up an arbitrary choice and get relative sizes that way.

2.Ionization Energy: the amount of energy it takes to pull an electron completely off an atom. ALWAYS endothermic.

3.Electron Affinity

So What is Ours Good At?Three new things:

1.Atomic radius: where you define the ‘end’ of an atom is a little nebulous, but we can make up an arbitrary choice and get relative sizes that way.

2.Ionization Energy: the amount of energy it takes to pull an electron completely off an atom. ALWAYS endothermic.

3.Electron Affinity: the amount of energy you get out from adding an electron to an atom. Exothermic.

Atomic RadiusTwo factors:1.Where are the electrons (which orbitals)?2.How many protons are there?

Atomic RadiusTwo factors:1.Where are the electrons (which orbitals)? Bigger as you go down2.How many protons are there? Smaller as you go across

Radius of IonsCan only compare size of ions if:

1. Number of protons are the same: Mg vs Mg2+

OR 2. Number of electrons are the same: F— vs Mg2+

In both cases, the question comes down to the same questions as before:

1.Where are the electrons?2.How many protons are there (compared to how many electrons)?

Ionization EnergyFirst ionization energy: A A+

Second ionization energy: A+ A2+ (always more than first)Third ionization energy: A2+ A3+ (always more than second)Etc

Values come from….PES!

Ionization EnergyFirst ionization energy: A A+

Second ionization energy: A+ A2+ (always more than first)Third ionization energy: A2+ A3+ (always more than second)Etc

Values come from….PES!

Only the first ionization energy follows a trend.

The second and third and beyond depend more on where the electrons are

The second for sodium will be very high because you’re removing non-valence electrons. The second for magnesium will be lower because it’s also a valence electron.

Ionization Energy

Across a row: more protons holding onto the electronsDown a column: electrons are farther away and ‘shielded’ from nucleus.Can compare on one diagonal (Ge vs P) but not on other (Si vs As)

Electron AffinityA + e- A-

Rarely see second or third electron affinities, but technically possible.

ANNOYING FACT WARNING:

Almost always exothermic, but usually given as a positive number.

Electron AffinityThis mostly comes down to the same two factors:

1. Where are the electrons2. How many protons are there?

Electron AffinityA lot of exceptions in this one, mostly having to do with full or half-full orbitals.

Summary