Decoding the Periodic Table Periodicity Decoding the Periodic Table

Effective Nuclear Charge The charge of the nucleus that is felt by the valence electrons Symbol: Zeff Zeff = atomic number (Z) - # of core e- What is the effective nuclear charge for each of the 8 main groups?

Effective Nuclear Charge

Periodicity Rules In the same period: In the same group: Zeff increases going to the right In the same group: Distance between valence electrons and nucleus increases going down

Disclaimer! Transition metals are the worst…

Atomic Radius The distance from the center of the nucleus to the valence electrons in an atom When does atomic radius INCREASE in a period? As Zeff DECREASES (valence electrons are held less tightly) Moving to the LEFT When does atomic radius INCREASE in a group? As distance INCREASES Moving DOWN

Atomic Radius

Atomic Radius

Electronegativity The ability of a neutral atom to gain an electron When does electronegativity INCREASE in a period? As Zeff INCREASES (new valence electron is attracted by a stronger positive charge) Moving to the RIGHT When does electronegativity INCREASE in a group? As distance DECREASES (attractive force is stronger at smaller distances) Moving UP

Electronegativity

Electronegativity

First Ionization Energy The energy that it takes to remove one electron from a neutral atom When does 1st IE INCREASE in a period? As Zeff INCREASES (electron being removed is held more tightly) Moving to the RIGHT When does 1st IE INCREASE in a group? As distance DECREASES (attractive force is stronger at smaller distances) Moving UP

1st Ionization Energy

1st IE: Main Groups

First Ionization Energy

Ionic Radius: Cations The distance from the center of the nucleus to the valence electrons in a positively charged ion When does cation radius INCREASE in a period? As the number of electrons lost DECREASES (remaining electrons are pulled closer to nucleus) Moving to the LEFT When does cation radius INCREASE in a group? As distance INCREASES Moving DOWN

Ionic Radius: Anions The distance from the center of the nucleus to the valence electrons in a negatively charged ion When does anion radius INCREASE in a period? As the number of electrons gained INCREASES (valence electrons held less tightly) Moving to the LEFT When does anion radius INCREASE in a group? As distance INCREASES Moving DOWN

NOTE: Anions ALWAYS have larger ionic radii than cations! Why is this?

Ionic Radius

Ionic Radius

Warm-Up Rank the 4 Periodic Trends from what YOU think is easiest to hardest to understand. Atomic Radius Electronegativity 1st Ionization Energy Ionic Radius