Periodic Trends/Patterns

CH. 2

Periodic Trend

• Nuclear charge

• atomic size or radius

• ionization energy

• electron affinity

• electronegativity

• metallic character

• Reactivity

• bonding characteristics

• crystal configurations

• acidic properties

• densities

Quantum Mechanical Model

Effective Nuclear Charge: The s, p, d, and f orbitals within a given shell have slightly different energies.

The difference in energies between subshells result in electron–electron repulsion which shields outer electrons from the nucleus.

The net nuclear charge felt by an electron is called the effective nuclear charge ( Zeff ).

Zeff

Quantum Mechanical Model

Zeff is lower than actual nuclear charge.

Zeff increases toward nucleus ns > np > nd > nf

This explains certain periodic changes observed.

Z*

The effective nuclear charge in the actual

charge from the nucleus that an electron

feels due to attractive forces from the

nucleus but also repulsive forces from the

other electrons, mainly the core electrons.

Atomic radii

The Periodic Table 02

Periodic Properties 02

Atomic Radii 02:

Chapter 06 9

Ions and Ionic Radii02

Ions and Ionic Radii

Trend of ionic radii

The cation of an atom decreases in size while the

anion of an atom increases in size.

The trend can not be made according to the periodic

table, but by the isoelectronic series.

The more positive an ion is the smaller it is because

Zeff increases, while the more negative an ion, the

larger it is because Zeff decreases.

Ionization EnergyDefined as the amount of energy necessary to

remove the outermost electron from an isolated neutral atom in the gaseous state to infinity.

Abbreviation is Ei, it has units of kJ/mol.

IE

successive ionization energy

Ionization Energy

Minor irregularities in the Ei values are explained by looking at the electron configurations.

IE Trend

Ionization Energy

Ionization energies vary periodically, which is explained by the changes in Zeff .

Zeff

Electron Affinity 01

Electron Energy: Energy change that occurs when an electron is added to an isolated atom in the gaseous state.

Abbreviation is Eea, it has units of kJ/mol. Values are generally negative because energy is released.

Value of Eea results from interplay of nucleus electron attraction, and electron–electron repulsion.

EA

Electron Affinity 02

EA Trend

Periodic properties REACTIVITY - Li

Periodic properties - Na

Periodic properties - K

Metallic Character

• The metallic character of atoms can be

related to the desire to loose electrons

• On the periodic table, the metallic character

of the atoms increase down a family and

decreases from left to right across a period.

Periodic Trend Activities

• WebElements

• Periodicity and Properties of Elements and Compounds: An Internet Study

• Periodic Trends Lesson

• Periodic Table Exercises

• Our Favorite Element

• Structured Curriculum Lesson Plans