Periodic Properties and Atomic Structure: Study Notes for General Chemistry

Periodic Properties of the Elements

Structure of the Periodic Table

The periodic table organizes elements based on their atomic structure and recurring chemical properties. Elements are arranged in rows called periods and columns called groups.

• Groups: Elements in the same column have similar valence electron configurations and chemical properties.

• Periods: Elements in the same row have the same number of electron shells.

• Group Number: Indicates the number of valence electrons for main group elements.

• Period Number: Indicates the number of electron shells.

Classification of Elements

Elements are classified into several groups based on their properties:

• Group 1: Alkali Metals

• Group 2: Alkaline Earth Metals

• Group 3-12: Transition Metals

• Group 13-16: Metalloids

• Group 17: Halogens

• Group 18: Noble Gases

Example: Magnesium (Mg) belongs to the Alkaline Earth Metals (Group 2).

Periodic Properties: Introduction

Oxidation Potential

Oxidation potential measures the ability of an atom to lose electrons (oxidize) or gain electrons (reduce). Transition metals often have multiple oxidation states.

Transition Metals

Transition metals are separated from the main group elements and exhibit unique properties, such as variable oxidation states and colored compounds.

Metals vs. Nonmetals

Metals and nonmetals differ in their physical and chemical properties:

• Metals: Malleable, lustrous, good conductors of electricity and heat, form basic oxides, and generally have high melting and boiling points.

• Nonmetals: Brittle, dull, poor conductors of electricity and heat, form acidic oxides, and generally have low melting and boiling points.

Periodic Properties: Atomic Structure and Trends

Atomic Radius

The atomic radius is the distance from the nucleus to the outermost electron shell. It varies across periods and groups:

• Down a group: Atomic radius increases due to the addition of electron shells.

• Across a period (left to right): Atomic radius decreases as nuclear charge increases, pulling electrons closer to the nucleus.

Effective Nuclear Charge (Zeff)

Effective nuclear charge is the net positive charge experienced by valence electrons. It is calculated as:

• $Z_{\text{eff}} = Z - S$

• Where Z is the atomic number and S is the shielding constant.

Across a period, Zeff increases, making electrons more tightly bound to the nucleus.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom.

• Across a period: Ionization energy increases as Zeff increases.

• Down a group: Ionization energy decreases as electrons are farther from the nucleus.

Successive Ionization Energies

After the removal of one electron, atoms can have second, third, or higher ionization energies. Each successive ionization requires more energy, especially when removing electrons from a stable shell.

Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral atom.

• Across a period: Electron affinity increases (becomes more negative).

• Down a group: Electron affinity decreases.

Electronegativity

Electronegativity is the tendency of an atom to attract electrons in a chemical bond.

• Across a period: Electronegativity increases.

• Down a group: Electronegativity decreases.

Periodic Trends Summary

Summary of Periodic Trends

The periodic table shows clear trends in atomic properties:

• Metallic Character: Increases down a group, decreases across a period.

• Atomic Radius: Increases down a group, decreases across a period.

• Ionization Energy: Decreases down a group, increases across a period.

• Electron Affinity: Decreases down a group, increases across a period.

• Electronegativity: Decreases down a group, increases across a period.

Atomic Structure

Structure of an Atom

An atom consists of a nucleus (containing protons and neutrons) and electrons orbiting the nucleus. The nucleus is positively charged, while electrons are negatively charged.

• Protons: Positively charged, determine atomic number.

• Neutrons: Neutral, contribute to atomic mass.

• Electrons: Negatively charged, occupy energy levels.

Key Points about Atoms

• All matter is made of atoms, which are indivisible.

• Atoms of the same element are identical in mass and properties.

• Atoms combine in fixed ratios to form compounds.

• Chemical reactions involve rearrangement of atoms.

Additional info:

• Some diagrams and tables were inferred for clarity and completeness.

• Periodic trends and atomic structure are foundational concepts for understanding chemical reactivity and bonding.