Periodic Trends

Atomic Radius The distance from the nucleus out to the valence shell (outermost energy level occupied by electrons) Measured in angstroms ( )

How Radius Is measured The point at which the valence shell “ends” is difficult to measure. Instead, the distance between the nuclei of 2 bonded atoms is divided by 2, as nuclei are more easily detected

Atomic Properties affecting radius Energy Levels: The more energy levels required to hold an atom’s electrons, the larger the radius will be. As each energy level gets further and further from the nucleus.

Atomic Properties affecting radius Electron Shielding: Core electrons block (shield) the positive charge of the nucleus that the outer (valence) electrons feel.

Atomic Properties affecting radius Electron Shielding: The more core electrons present, the more shielding of the nuclear charge. The more the positive charge is shielded, the larger the radius will be as the attraction force between the electrons and protons will be less.

Atomic Properties affecting radius Nuclear Charge The overall positive charge emitted from the nucleus due to the number of protons present. The more protons in the nucleus, the greater the charge. The greater the nuclear charge, the greater the attractive force between the nucleus and the orbiting electrons, the smaller the radius.

Nuclear Charge vs. electron shielding Nuclear charge & electron shielding work against each other, often canceling each other out. This results in an “effective nuclear charge”, or the charge valence electrons actually feel after the affects of shielding by core electrons. What is the effective charge felt by sodium’s 1 valence electron?

Effective Nuclear Charge

Periodic Trend for radius Increases down a group, decreases across a period. Why?!

Explaining Radius trends Down a group Reason:

Explaining Radius trends Across a period Reason:

Affects of Atomic Radius Atomic Radius is the determining factor behind the characteristics of Electronegativity and Ionization Energy. In other words, you can explain why an atom has a certain electronegativity or ionization energy by referencing its radius.

Electronegativity The ability of an atom to attract another atom’s valence electrons towards itself.

Electronegativity Remember that, when atoms bond, they attempt to share or give/receive valence electrons. Electronegativity is a measure of how well an atom can steal away another atom’s valence electrons.

Electronegativity Radius is the determining factor for electronegativity. The closer an atom can get it’s nucleus (positive attractive force) to the valence electron it is trying to steal, the more it can attract it

Electronegativity When we say the radius is the determining factor for electronegativity, we are also saying that the balance between the nuclear charge, electron shielding, and the number of energy levels determines electronegativity Because they determine radius!

Trends for Electronegativity Radius and Electronegativity are inversely related (as one increases, the other decreases)

Ionization energy The energy required to remove a valence electron from an atom (how hard it is to remove).

Ionization energy Radius is the determining factor for ionization energy. The closer an atom’s nucleus (positive attractive force) is to it’s own valence electrons the more it can attract them and the harder they will be to remove.

Ionization energy Again, when we say the radius is the determining factor for ionization energy, we are also saying that the balance between the nuclear charge, electron shielding, and the number of energy levels determines ionization energy. Because they determine radius!

Trends for ionization energy Radius and Ionization Energy are inversely related (as one increases, the other decreases)

Ionization Energy and Electronegativity Both ionization energy and electronegativity describe how an atom handles valence electrons Whether it is good at taking electrons or good at giving them Therefore, it should be no surprise that we use this information to determine how they bond and what types of bonds these atoms make! Bonds