## Periodic Trends

Maureen_Guthormsen_1C
Posts: 2
Joined: Wed Sep 21, 2016 3:00 pm

### Periodic Trends

Any tips on memorizing periodic trends -- i.e. ionization energy, atomic radius, and electron affinity? I tend to mix up the directions of increasing and decreasing, so thank you for any input!!

Ryan Clydesdale
Posts: 7
Joined: Fri Jul 15, 2016 3:00 am

### Re: Periodic Trends

The easiest way for me is by thinking about the 4 corners of the periodic table and remember the properties of those 4 elements and then reason it out from there

Yuchien Ma 2L
Posts: 46
Joined: Wed Sep 21, 2016 2:58 pm

### Re: Periodic Trends

Most periodic trends such as electronegativity and ionization energies goes up and right, only atomic radius is the exact opposite; it goes left and down. That's how I remember it.
Hope this helps!

Simon Kapler 3I
Posts: 15
Joined: Mon Sep 26, 2016 3:01 am

### Re: Periodic Trends

At my high school, I was taught that pretty much all of the periodic trends can be explained by Zeff. Zeff is the effective nuclear charge, or how tightly the nucleus holds on to its outer electrons. As you go right across a period, both protons and electrons are added. Zeff increases because the positive charge of the nucleus increases while the outermost electrons stay the same distance from the nucleus (filling the same orbital). In other words, going across a period, the outermost electrons are more tightly held. This explains the trend in atomic radius.

Zeff can also be used to explain the Ionization Energy trend. Since IE is the amount of energy required to remove an electron from a gas-phase atom, valence electrons of elements with high Zeff require more energy to be removed (higher IE going right on the periodic table). Furthermore, removing an electron only increases the relative positive charge of the nucleus (increasing Zeff; picture it like a decrease in the atomic radius), pulling the outer electrons closer to the nucleus, which explains why the second IE > first IE.

Thinking about the periodic trends in terms of how they actually arise (the strength of the attractions/repulsions between protons and electrons) helps me visualize them and reason through questions better than just memorizing the pictures of arrows on the periodic table.