Atoms and Their Structure

Subatomic Particles

Atoms are composed of three fundamental subatomic particles: protons, neutrons, and electrons. The arrangement and number of these particles determine the chemical properties of each element.

• Protons: Positively charged particles found in the nucleus. The number of protons defines the atomic number (Z) and the identity of the element.

• Neutrons: Neutral particles found in the nucleus. The number of neutrons, together with protons, determines the mass number (A).

• Electrons: Negatively charged particles that orbit the nucleus in shells. In a neutral atom, the number of electrons equals the number of protons.

• Example: Bromine (Br) has atomic number 35 and mass number 80. It contains 35 protons, 45 neutrons (80-35), and 35 electrons.

The Periodic Table and Periodic Law

Organization of the Periodic Table

The periodic table arranges elements by increasing atomic number. Elements are grouped into periods (horizontal rows) and groups (vertical columns), reflecting recurring chemical properties.

• Periodic Law: The physical and chemical properties of elements are periodic functions of their atomic numbers.

• Periods: Horizontal rows; elements in the same period have the same number of electron shells.

• Groups: Vertical columns; elements in the same group have similar chemical properties due to similar valence electron configurations.

• Main Groups: Groups 1A to 8A are called representative elements.

Classification of Elements

Elements are classified as metals, nonmetals, or metalloids based on their physical and chemical properties.

• Metals: High conductivity, malleability, ductility, and metallic luster. Most are solid at room temperature.

• Nonmetals: Poor conductors, often powdery solids or gases, dull appearance.

• Metalloids: Intermediate properties; can be shiny or dull, brittle, moderate conductivity. Used as semiconductors.

Groups and Periods: Identifying Elements

Group and Period Assignment

Each element can be identified by its group and period, which determines its chemical behavior.

• Example: Selenium (Se, atomic number 34) is in Group 6A, Period 4. Calcium (Ca, atomic number 20) is in Group 2A, Period 4. Boron (B, atomic number 5) is in Group 3A, Period 2.

Similar Chemical Properties

Elements in the same group exhibit similar chemical properties. For example, noble gases (Group 8A) are inert, while alkali metals (Group 1A) are highly reactive.

• Example: Krypton (Kr) and Neon (Ne) are both noble gases in Group 8A and share similar properties.

Electronic Structure and Valence Electrons

Electron Shells and Valence Electrons

Electrons are arranged in shells around the nucleus. The outermost shell contains the valence electrons, which determine an element's chemical reactivity.

• Valence Electrons: The number of valence electrons corresponds to the group number for main group elements.

• Example: Aluminum (Group 3A) has 3 valence electrons; Oxygen (Group 6A) has 6 valence electrons.

The Octet Rule

The octet rule states that elements tend to react to achieve eight electrons in their valence shell, attaining the stable configuration of a noble gas.

• Elements on the right: Gain electrons to reach the next noble gas.

• Elements on the left: Lose electrons to reach the previous noble gas.

• Result: Atoms gain, lose, or share electrons to achieve a stable octet.

Ions and Their Formation

Cations and Anions

Ions are charged particles formed when atoms gain or lose electrons.

• Cation: Positively charged ion formed by loss of electrons (e.g., Na → Na+ + 1e-).

• Anion: Negatively charged ion formed by gain of electrons (e.g., F + 1e- → F-).

• Group Trends: All atoms in a group lose or gain the same number of electrons, resulting in ions with similar charges.

Examples of Ion Formation

• Aluminum (Al): Group 3A, forms Al3+ by losing 3 electrons.

• Oxygen (O): Group 6A, forms O2- by gaining 2 electrons.

Summary Table: Groups and Common Properties

Main Groups and Their Properties

Additional info:

• The lecture and lab schedules confirm coverage of all relevant chapters, including atomic structure, periodic table, ions, and chemical compounds.

• Images included are directly relevant to the explanation of atomic structure, periodic table organization, and ion formation.