The Periodic Law Electron Configuration and Periodic Properties

What do we already know? Elements are arranged in the periodic table by atomic number. Elements are arranged in the periodic table by atomic number. Rough correlation between element arrangement and electron configuration. Rough correlation between element arrangement and electron configuration. More relationships between periodic law and electron configurations. More relationships between periodic law and electron configurations.

Atomic Radii Atomic radius may be defined as one-half the distance between the nuclei of identical atoms that are bonded together. Atomic radius may be defined as one-half the distance between the nuclei of identical atoms that are bonded together. In general, atomic radii decrease from left to right across a period and increase down a group. In general, atomic radii decrease from left to right across a period and increase down a group. The trend to smaller atoms across a period is caused by increasing + charge of the nucleus. The trend to smaller atoms across a period is caused by increasing + charge of the nucleus.

Atomic Radii Trends

Ionization Energy An ion is an atom that has a + or – charge. An ion is an atom that has a + or – charge. Any process that results in the formation of an ion is referred to as ionization. Any process that results in the formation of an ion is referred to as ionization. First ionization energies increase across a period and decrease down a group. First ionization energies increase across a period and decrease down a group. The energy required to remove one electron from a neutral atom is the ionization energy (kJ/mol). The energy required to remove one electron from a neutral atom is the ionization energy (kJ/mol).

Ionization Energy Group 1 Elements have relatively small ionization energies because they do not require much energy to detach one electron. Na – 496 kJ/mol

Ionization Energy vs. Z

Electron Affinity Energy change resulting from the addition of an electron is electron affinity. Energy change resulting from the addition of an electron is electron affinity. The halogens have high electron affinities because the addition of an electron to an atom results in a completely filled shell. The halogens have high electron affinities because the addition of an electron to an atom results in a completely filled shell. The noble gases have electron affinities of zero. The noble gases have electron affinities of zero.

Electron Affinity Electron affinity tends to increase across a period. Electron affinity tends to increase across a period. Some irregularities due to extra stability of half or filled sublevels. Some irregularities due to extra stability of half or filled sublevels. Electron affinity tends to decrease down a group. Electron affinity tends to decrease down a group. Added electrons are farther from the nucleus Added electrons are farther from the nucleus

Electron Affinity

Electronegativity Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons. Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons. Electronegativities tend to increase across each period, or decrease down a group. Electronegativities tend to increase across each period, or decrease down a group. Elements with high ionization energies have high electronegativities due to the strong pull exerted on electrons by the nucleus. Elements with high ionization energies have high electronegativities due to the strong pull exerted on electrons by the nucleus.

Ionic Radii A positive ion is known as a cation. A positive ion is known as a cation. The formation of a cation by the loss of electrons leads to a decrease in radius. The formation of a cation by the loss of electrons leads to a decrease in radius. A negative ion is known as an anion. A negative ion is known as an anion. The formation of an anion by the addition of electrons always leads to an increase in atomic radius. The formation of an anion by the addition of electrons always leads to an increase in atomic radius.

Valence Electrons The electrons available to be lost, gained, or shared in the formation of chemical compounds are referred to as valence electrons. The electrons available to be lost, gained, or shared in the formation of chemical compounds are referred to as valence electrons. Main-groups elements valence electrons correspond to their group configuration, i.e. Group 1 – 1 valence, 2-2, 13-3, 14-4, etc. Main-groups elements valence electrons correspond to their group configuration, i.e. Group 1 – 1 valence, 2-2, 13-3, 14-4, etc.

Summary of Major Trends Moving Left --> Right. Moving Left --> Right. Atomic Radius Decreases Atomic Radius Decreases Ionic Radius Decreases Ionic Radius Decreases Ionization Energy Increases Ionization Energy Increases Electron Affinity Increases Electron Affinity Increases Electronegativity Increases Electronegativity Increases Moving Top --> Bottom. Moving Top --> Bottom. Atomic Radius Increases Atomic Radius Increases Ionic Radius Increases Ionic Radius Increases Ionization Energy Decreases Ionization Energy Decreases Electron Affinity Decreases Electron Affinity Decreases Electronegativity Decreases Electronegativity Decreases