Periodic Table and Classification of Elements

Periodic Law and Structure of the Periodic Table

The Periodic Law states that when elements are arranged in order of increasing atomic number, certain sets of properties recur periodically. The periodic table organizes elements into rows and columns based on these recurring properties.

• Periods: Horizontal rows in the periodic table.

• Groups (or Families): Vertical columns in the periodic table.

• Main-Group Elements: Groups 1A (IA) to 8A (VIIIA).

• Transition Elements/Metals: Groups 3B (IIIB) to 8B (VIIIB) and 1B (IB) to 2B (IIB).

• Inner Transition Elements: The two rows below the main table (lanthanides and actinides).

Group Names:

• Group 1A (except H): Alkali Metals

• Group 2A: Alkaline Earth Metals

• Group 5A: Pnictogens

• Group 6A: Chalcogens

• Group 7A: Halogens

• Group 8A: Noble Gases

Additional info: Hydrogen is unique and not considered an alkali metal, though it is placed in Group 1A.

Classification of Elements: Metals, Nonmetals, and Metalloids

• Metals (GY): Elements that are typically shiny, good conductors of heat and electricity, malleable, and ductile. Most are solid at room temperature (except mercury).

• Nonmetals (=): Elements that are dull in appearance, poor conductors of heat and electricity, and are not malleable or ductile. They can be solid, liquid, or gas at room temperature.

• Metalloids (GZ): Elements with properties intermediate between metals and nonmetals. They are semiconductors.

Properties of Metals, Nonmetals, and Metalloids

Additional info: Metalloids include elements like Si, B, and As.

Atoms, Ions, and the Formation of Ions

Atoms and Ions

An atom is the smallest unit of an element that retains its chemical properties. An ion is an atom or molecule that has gained or lost one or more electrons, resulting in a net charge.

• Cation: A positively charged ion (loss of electrons).

• Anion: A negatively charged ion (gain of electrons).

Atoms tend to gain or lose electrons to achieve the same number of electrons as the nearest noble gas, resulting in a stable electron configuration.

• Example: Na atom (11 electrons) loses 1 electron to become Na+ (10 electrons, like Ne).

• Example: K atom (19 electrons) loses 1 electron to become K+ (18 electrons, like Ar).

Types of Elements: Atomic and Molecular

Atomic Elements

An atomic element exists in nature with single atoms as its basic unit (e.g., Na, Fe).

Molecular Elements

A molecular element exists in nature as molecules, which are two or more atoms bonded together. The most common are diatomic elements:

• H2, N2, O2, F2, Cl2, Br2, I2

Chemical Bonds and Compounds

Types of Chemical Bonds

• Ionic Bond: Formed when electrons are transferred from one atom (usually a metal) to another (usually a nonmetal), resulting in the attraction between oppositely charged ions.

• Covalent Bond: Formed when two or more nonmetals share electrons.

Types of Compounds

• Ionic Compounds: Composed of cations (usually metals) and anions (usually nonmetals) held together by ionic bonds. Example: NaCl, MgO, CaF2.

• Covalent (Molecular) Compounds: Composed of two or more nonmetals held together by covalent bonds. Example: CO2, H2O, PF5.

Chemical Formulas

Molecular and Empirical Formulas

• Molecular Formula: Shows the actual number of atoms of each element in a molecule. Example: N2O4.

• Empirical Formula: Shows the simplest whole-number ratio of atoms in a compound. Example: NO2 for dinitrogen tetroxide.

The formula unit is the smallest whole-number ratio of ions in an ionic compound, representing its empirical formula.

Naming Binary Ionic Compounds

Rules for Naming Binary Ionic Compounds (with Metals Forming Only One Type of Cation)

• Name the metal (cation) first.

• Name the nonmetal (anion) second, changing its ending to -ide.

• Example: CaO is named calcium oxide.

Additional info: For metals that can form more than one type of cation (such as transition metals), a Roman numeral is used to indicate the charge.