Periodic Properties of the Elements

Elemental Patterns and the Periodic Law

The periodic table organizes elements based on recurring patterns in their physical and chemical properties. These patterns, known as periodic properties, allow scientists to predict the behavior of elements and the existence of undiscovered elements.

• Periodic property: A property predictable based on an element’s position in the periodic table.

• Example: Density increases as you move down a column in the periodic table.

Mendeleev’s Periodic Law: When elements are arranged in order of increasing mass, certain sets of properties recur periodically.

Mendeleev’s periodic table organized elements so that those with similar properties fell into the same columns, allowing predictions of undiscovered elements.

The Modern Periodic Table

Today, elements are arranged by increasing atomic number. Rows are called periods, and columns are called groups or families. Elements in a group have similar properties.

• Main-group elements: Properties are largely predictable based on position.

• Transition and inner transition elements: Properties are less predictable.

Classification of Elements

• Metals: Conduct heat and electricity, malleable, ductile, shiny.

• Nonmetals: Insulators, brittle, dull.

• Metalloids: Exhibit properties intermediate between metals and nonmetals.

Quantum Theory and Electron Configuration

Electron Configuration

Quantum-mechanical theory describes the arrangement of electrons in atoms. Electrons occupy orbitals, and their arrangement is called the electron configuration.

• Schrödinger’s equation: For hydrogen, the electron occupies the lowest energy orbital.

• For multi-electron atoms, electron–electron interactions complicate the solution, but orbitals remain hydrogen-like.

Electron Spin and the Pauli Exclusion Principle

Electrons possess a property called spin, described by the spin quantum number (). Each orbital can hold two electrons with opposite spins.

• Spin quantum number (): Can be or .

• Pauli Exclusion Principle: No two electrons in an atom can have the same set of four quantum numbers.

Sublevel Energy Splitting, Shielding, and Penetration

In multi-electron atoms, sublevels split in energy due to charge interactions, shielding, and penetration.

• Degenerate orbitals: Orbitals with the same energy.

• Shielding: Electrons block the attraction between other electrons and the nucleus.

• Penetration: Electrons in orbitals closer to the nucleus experience greater attraction.

Energy Ordering of Orbitals

Electrons fill orbitals from lowest to highest energy, following the aufbau principle.

• Order of filling:

Hund’s Rule

When filling orbitals of equal energy, electrons occupy them singly with parallel spins before pairing.

Electron Configuration and the Periodic Table

Core and Valence Electrons

Core electrons are in lower-energy shells, while valence electrons are in the outermost shell and participate in bonding.

Orbital Blocks

The periodic table is divided into four blocks (s, p, d, f) based on the filling of quantum sublevels.

• Group number: Equals the number of valence electrons for main-group elements.

• Row number: Equals the highest principal quantum number.

Writing Electron Configurations from the Periodic Table

Electron configurations can be written using the periodic table by locating the element, identifying the preceding noble gas, and tracing the blocks to assign electrons.

Transition and Inner Transition Metals

Transition metals (d block) and inner transition metals (f block) often have irregular electron configurations due to sublevel splitting. Some anomalies occur when electrons jump to d orbitals to create half-filled or fully filled sublevels.

Periodic Trends and Elemental Properties

Atomic Radii

The atomic radius is the average distance from the nucleus to the outermost electron. It increases down a group and decreases across a period.

Ionization Energy

Ionization energy (IE) is the minimum energy required to remove an electron from an atom in the gas phase. It decreases down a group and increases across a period.

• First ionization energy: Energy to remove the first electron.

• Successive ionization energies: Each successive removal requires more energy, with a large jump when core electrons are removed.

Electron Affinity

Electron affinity (EA) is the energy change associated with the addition of an electron to an atom. EA generally becomes more negative across a period, with halogens having the highest EA.

Metallic Character

Metallic character describes how closely an element’s properties match those of a metal. It increases down a group and decreases across a period.

Summary Table: Periodic Properties

Periodic properties such as atomic radius, ionization energy, electron affinity, and metallic character follow predictable trends based on an element’s position in the periodic table.

Practice and Problem Solving

Writing Electron Configurations

• Locate the element and determine its atomic number.

• Distribute electrons in orbitals following the order of filling.

• Each orbital holds a maximum of two electrons.

Predicting Ionic Charge

• Metals lose electrons to form cations with the same electron configuration as the nearest noble gas.

• Nonmetals gain electrons to form anions with the same electron configuration as the nearest noble gas.

Magnetic Properties of Ions

• Paramagnetism: Unpaired electrons result in a net magnetic field.

• Diamagnetism: All electrons are paired; no net magnetic field.

Radii of Atoms and Ions

• Cations are smaller than their neutral atoms.

• Anions are larger than their neutral atoms.

• Ion size increases down a group and decreases across a period for isoelectronic species.

Characteristics of Metals vs. Nonmetals

Conclusion

Understanding periodic properties and electron configurations is fundamental to predicting the behavior of elements and their compounds. The periodic table serves as a powerful tool for organizing chemical knowledge and guiding problem solving in general chemistry.