Chemistry - Periodic Trends

Atomic radius

Distance from the center of the nucleus to the "edge" of the electron cloud.

What is the trend for atomic radius in a vertical column?
Why does this trend happen?

The atomic radius goes from smaller at the top to larger at the bottom because each step down the family adds a new energy level to the electron cloud, making the atoms larger with each step.

What is the trend for atomic radius in a horizontal row?
Why does this trend happen?

Atoms get smaller each step from left to right across a period because each step from left to right adds a proton and an electron (and 1 or 2 neutrons), the electrons are added to already existing energy levels. The nucleus is more positive and the electron cloud is more negative which increases the attraction and pulls the cloud in towards the nucleus, making the atom smaller with each step from left to right. (Effective nuclear charge increases)

Why does the ionization energy decrease as atomic radius increases?

This concept is called shielding. As more energy levels are added to atoms, the inner layers of electrons shield the outer electrons from the nucleus, the effective nuclear charge on those outer electrons is less so the outer electrons are less tightly held.

Ionization energy

The energy required to remove an electron from an atom

Effective nuclear charge

Net positive charge experienced by valence electrons.

How is an atom ionized?

If an electron is given enough energy to overcome the effective nuclear charge holding the electron in the cloud, it can leave the atom completely, which ionizes or charges the atom because the protons and electrons are not equal.

Ionization energy and _______ ______ are inversely proportional

Atomic radius

Electronegativity

Measure of an atom's attraction for another atom's electrons.
(Arbitrary scale ranges from 0-4)

Metals are generally electron ______, and have ______ electronegatives.

givers, low

Nonmetals are generally electron _______, and have ______ electronegatives.

takers, high

The most reactive metals are the _______ because...

largest because they're the best electron givers

The most reactive nonmetals are the _______ because...

smallest because they're the best electron takers

What is a cation? What is an anion?

A cation loses an electron and is positively charged. An anion gains an electron and is negatively charged

Cations are always _______ than the original atom because...

smaller, the entire outer energy level is removed during ionization (effective nuclear charge increases)

Anions are always _______ than the original atom because....

larger, electrons are added to the outer energy level and negative repels negative (effective nuclear charge decreases)

What is the trend for ionization energy in a vertical column?
Why does this trend happen?

The ionization energy decreases going down a family because atomic radius increases going down a group, so the attraction between the nucleus and valence electrons is weaker (due to shielding).

What is the trend for ionization energy in a horizontal row?
Why does this trend happen?

The ionization energy increases going right in a period because protons are being added to the atom but no electron are being added to the inner energy level, which increases the effective nuclear charge. Therefore, the valence electrons are held more tightly and the atom shrinks in size, so, difficulty to remove the electrons increases.

What is the trend for electronegativity in a vertical column?
Why does this trend happen?

Down a group, electronegativity decreases because the atomic radius increases and effective nuclear charge and shielding effect decreases.

What is the trend for electronegativity in a horizontal row?
Why does this trend happen?

Across a period, electronegativity increases because the number of charges on the nucleus increases. That attracts the bonding pair of electrons more strongly.