Chapter 3: Periodic Properties of the Elements

Hund’s Rule

When filling orbitals that have the same energy (degenerate), place one electron in each orbital before completing pairs

Aufbau Principle

Energy levels and sublevels fill from lowest energy to highest: s → p → d → f; orbitals that are in the same sublevel (l value) have the same energy

Pauli Exclusion Principle

There can be no more than two electrons per orbital

Core electrons

Electrons in lower energy shells

Valence electrons

The electrons in all the sublevels with the highest principal energy shell

Halogens

Nonmetals with one fewer electron than the next noble gas

Noble gases

Have 8 valence electrons except for He

Paramagnetism

Electron configurations that result in unpaired electrons mean that the atom or ion will have a net magnetic field

Dimagnetism

Electron configurations that result in all paired electrons mean that the atom or ion will have no magnetic field

Ionic Radii Rules

More electrons = larger

Ions in the same group have the same charge

Ion size increases down the column.

Higher valence shell, larger

Cations are smaller than neutral atoms; anions are larger than neutral atoms.

All cations are smaller than anions (Except Rb+ and Cs+, which are bigger than or the same size as F− and O2−).

Isoelectric Species Rules

Larger positive charge = smaller cation

Larger negative charge = larger anion

Ionization Energy (IE)

The minimum energy needed to remove an electron from an atom or ion in the gas phase; an endothermic process (requires the input of energy to remove the electron; lower IE, farther electron distance from nucleus = easier to remove

Ionization Energy Trend (IE Trend)

Decreases down the group; valence electron is farther from the positively charged nucleus with the same effective nuclear charge; increases across the period

Electron Affinity (EA)

The energy associated with adding an electron to the valence shell of an atom that is in the gas phase; an exothermic, but sometimes endothermic process; more energy released (more negative) = larger EA

Metal texture

Malleable (deform under compressive stress) and ductile (stretch under tensile stress)

Metal reflectiveness

Shiny, lustrous, reflect light

Metal conductivity

Conduct heat and electricity quickly

Metal oxides

Most oxides basic and ionic

Metal electron behavior

Lose electrons in reactions to form cations—oxidized

Nonmetal texture

Brittle in solid state

Nonmetal reflectiveness

Dull, nonreflective, solid surface

Nonmetal conductivity

Electrical and thermal insulators

Nonmetal oxides

Most oxides acidic and molecular

Nonmetal electron behavior 

Gain electrons in reactions to form anions and polyatomic anions—reduced

Metallic character

How closely an element’s properties match the ideal properties of a metal

Ionic charges

Periodic Trends