Atoms and Their Structure

Subatomic Particles

Atoms are the basic units of matter, composed of three main subatomic particles: protons, neutrons, and electrons.

• Protons (p+): Positively charged particles found in the nucleus of an atom.

• Neutrons (n0): Neutral particles (no charge) also located in the nucleus.

• Electrons (e-): Negatively charged particles that orbit the nucleus in electron shells.

Atomic Number (Z): The number of protons in an atom, which defines the element.

Mass Number (A): The sum of protons and neutrons in the nucleus.

Example: Carbon-12 has 6 protons and 6 neutrons, so its mass number is 12.

Exceptions and Special Cases

• Hydrogen: The most common isotope of hydrogen has no neutrons (only 1 proton and 1 electron).

• Isotopes: Atoms of the same element with different numbers of neutrons. For example, Carbon-14 has 6 protons and 8 neutrons.

Additional info: Isotopes can be stable or unstable (radioactive). Radioactive isotopes emit high-energy particles as they decay to become more stable.

Ions: Charged Atoms

Formation and Types of Ions

Ions are atoms or molecules that have gained or lost electrons, resulting in a net electrical charge.

• Anion: An ion with more electrons than protons, giving it a negative charge. Example: Cl- (chloride ion).

• Cation: An ion with more protons than electrons, giving it a positive charge. Example: Na+ (sodium ion).

Additional info: Ions are essential in biological processes such as nerve impulse transmission and muscle contraction.

Isotopes and Radioactivity

Definition and Importance

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons.

• Stable Isotopes: Do not change or decay over time.

• Radioactive Isotopes: Unstable; they emit radiation as they decay to a more stable form.

Example: Carbon-14 is a radioactive isotope used in radiocarbon dating.

Molecules and Chemical Bonds

Definition of Molecules

A molecule is formed when two or more atoms bond together chemically. Molecules can consist of the same or different elements.

• Example: O2 (oxygen gas), H2O (water)

Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules and compounds. The main types of chemical bonds include:

• Covalent Bonds: Atoms share pairs of valence electrons. These can be further classified as:

  • Nonpolar Covalent Bonds: Electrons are shared equally between atoms (e.g., O2).

  • Polar Covalent Bonds: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Ionic Bonds: Formed when one atom donates an electron to another, resulting in oppositely charged ions that attract each other (e.g., NaCl).

• Hydrogen Bonds: Weak attractions between a hydrogen atom (covalently bonded to a more electronegative atom) and another electronegative atom (e.g., between water molecules).

Summary Table: Types of Chemical Bonds

Key Terms and Definitions

• Atom: The smallest unit of an element that retains its chemical properties.

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Molecule: Two or more atoms bonded together.

• Covalent Bond: A chemical bond formed by the sharing of electron pairs between atoms.

• Ionic Bond: A chemical bond formed by the electrostatic attraction between oppositely charged ions.

• Hydrogen Bond: A weak bond between two molecules resulting from an electrostatic attraction.

Additional Academic Context

• Atoms seek to achieve a stable electron configuration, often resembling the nearest noble gas. This drives the formation of ions and chemical bonds.

• Radioactive decay can be used in medicine (e.g., cancer treatment) and in dating ancient biological materials.