Chemical Elements: Properties, Structure, and Bonding Principles

Fundamental Properties of Elements

Classification of Elements

Metallic Properties

• Conductivity: Excellent conductors of heat and electricity.
• Physical State: Solid at room temperature, except for mercury (Hg), which is liquid.
• Ions: Tend to lose electrons, forming positive ions (cations).
• Other Characteristics: Approximately 75% of all elements are metals. They possess metallic luster and are ductile.

Nonmetallic Properties

• Conductivity: Poor conductors of heat and electricity.
• Physical State: Can be solid (e.g., Carbon, Sulfur), liquid (e.g., Bromine), or gas (e.g., Oxygen, Nitrogen) at room temperature.
• Ions: Tend to gain electrons, forming negative ions (anions).
• Other Characteristics: Most nonmetal solids are soft.

Noble Gases

• Physical State: Gases at room temperature.
• Ions: Do not readily gain or lose electrons; they do not form ions because they are chemically very stable.
• Other Characteristics: Exist as isolated atoms in nature.

Atomic Structure and Configuration

Electron Energy Levels

The current atomic model explains that atoms have electrons ordered in orbits at different distances from the nucleus. These orbits represent different layers or levels of energy where electrons reside.

Periodic Table Organization

The Periodic Table organizes elements based on their atomic structure, leading to predictable properties.

Period Definition

All elements in the same period have their outermost electrons located in the same energy level.

Group Definition

All elements in the same group have the same number of valence electrons (electrons in the outermost level), which results in similar chemical properties.

Stability and Bonding Rules

Electron Configuration Rules: The first energy level can hold a maximum of 2 electrons. Subsequent levels typically hold a maximum of 8 electrons (for simplified valence shell rules).

Stable Configuration (Octet Rule): An atom achieves stability when it has 8 electrons in its outermost level (or 2 if it only has the first level). This principle explains why and how elements bond.

Chemical Bonding Types

A Chemical Bond is the force that holds atoms together to form a substance.

Bonding Principles

Atoms bond to achieve a stable configuration (a full outermost electron shell).

• Metals and Nonmetals: Form ionic networks (ionic bonds), where cations and anions bind.
• Nonmetals and Nonmetals: Form covalent networks or molecules (covalent bonds).
• Same Metal Element: Forms metallic networks (metallic bonds). Examples: Cu, Na, Ag.

Covalent Bonds and Molecules

A Covalent Bond is the union of two atoms sharing one or more pairs of electrons. This occurs typically between nonmetals.

A Molecular Form is formed by the union of two or more atoms via a covalent bond.

Ionic Bonds and Crystals

An Ionic Bond is the electrostatic force of attraction between cations and anions. It occurs typically between metals and nonmetals.

An Ionic Crystal is a structure where atoms are held together by ionic bonds in an orderly crystal lattice. This usually occurs between metals (which form cations) and nonmetals (which form anions).

Crystal Structure Definition

A Crystal is an orderly structure constituted by an undetermined number of atoms.

Periodic Table Classification (Mendeleev)

Dmitri Mendeleev ordered elements according to atomic mass and grouped them based on similar properties. He is credited with inventing the periodic table.

Elements in Biology (Bioelements)

Bioelements are chemical elements that are essential components of living beings.

Major Bioelements

The most abundant bioelements are C, H, O, N, Ca, P, Mg, S, Na, K, and Cl. These constitute over 99% of living matter.

Essential Trace Elements

These elements are present in a lower percentage (approximately 0.1%) in all organisms but are essential for life. Examples include Fe, Zn, Mn, F, I, Cu, and Co.