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Summary of Periodic Trends

Posted: Wed Oct 23, 2019 9:37 pm
by Ellis Song 4I
- Atomic radii increase down a group and decrease across a period
- Ionic radii increase down a group and decrease across a period, cations are smaller than parent and anions are larger
- Ionization energy decreases down a group and increases across a period
- Electron affinity is high for elements at the top right of the periodic table, noble gases have negative electron affinity

Re: Summary of Periodic Trends

Posted: Thu Oct 24, 2019 9:43 am
by Paige Lee 1A
Could someone please explain why noble gases have a negative electron affinity?

Re: Summary of Periodic Trends

Posted: Thu Oct 24, 2019 9:59 am
by TYun_1C
Since noble gases already have filled octets, they are extremely stable and do not want it gain another electron, which would make it much more unstable. Therefore, there is almost zero energy released (electron affinity) when an electron is added to a ground state noble gas,

Re: Summary of Periodic Trends

Posted: Thu Oct 24, 2019 10:23 am
by Jasmine Fendi 1D
Can someone please explain why ionization energy increases as you move from left to right on the periodic table?

Re: Summary of Periodic Trends

Posted: Thu Oct 24, 2019 1:03 pm
by alicechien_4F
Since ionization energy is the energy required to remove an electron from a neutral atom, atoms of the left side of the period table would have the lowest ionization energy because alkali metals want to lose electrons to maintain a full valence shell and become a cation. The lower the ionization energy, the easier it will be for an atom to be cation. On the other hand, atoms on the right side of the periodic table rather gain electrons than lose them, so it'll take much more energy to remove the electrons than to gain them. Hope this helps!

Re: Summary of Periodic Trends

Posted: Thu Oct 24, 2019 1:07 pm
by Yailin Romo 4G
Thank you for this helpful summary of periodic trends, what I would add to that table is which elements (metals, nonmetals) differ with their affinity and how their ionization energy differs as well.

Re: Summary of Periodic Trends

Posted: Thu Oct 24, 2019 1:16 pm
by Diana Chavez-Carrillo 2L
Is electron affinity only important/ only affects Group 17 (according to Lavelle) and noble gases? Or why is it important to know the electron affinity?

Re: Summary of Periodic Trends

Posted: Fri Oct 25, 2019 5:40 pm
by Alan Wu
Diana Chavez-Carrillo 3J wrote:Is electron affinity only important/ only affects Group 17 (according to Lavelle) and noble gases? Or why is it important to know the electron affinity?


It's important to know the electron affinity of elements probably because we can use that to measure how much energy is released or gained in reactions. Since electrons are lost and gained in reactions, the electron affinity and ionization energy can allow us to calculate the total energy of the reaction.