Atomic Structure

Subatomic Particles

Atoms are the basic units of matter, composed of three main subatomic particles: protons, neutrons, and electrons. Understanding their properties is essential for grasping chemical interactions in biological systems.

• Proton: Positively charged particle found in the nucleus of an atom.

• Neutron: Neutral particle also located in the nucleus.

• Electron: Negatively charged particle that orbits the nucleus in electron shells.

• Atomic Number: The number of protons in an atom, which determines the element's identity.

Example: Carbon has 6 protons, so its atomic number is 6.

Electron Shells and Chemical Behavior

The arrangement of electrons in shells around the nucleus determines how atoms interact and bond with each other.

• Valence Electrons: Electrons in the outermost shell; they play a key role in chemical bonding.

• Reactivity: Atoms with incomplete outer shells tend to form bonds to achieve stability.

Example: Sodium (Na) has one valence electron and readily loses it to form a stable ion.

Chemical Bonds

Types of Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds. The main types relevant to anatomy and physiology are:

• Ionic Bond: Formed by the attraction between oppositely charged ions (cation and anion). Occurs when one atom donates an electron to another.

• Covalent Bond: Formed when two atoms share electron pairs. Can be single, double, or triple bonds depending on the number of shared pairs.

• Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges within the molecule.

• Nonpolar Covalent Bond: Electrons are shared equally between atoms, resulting in no charge separation.

• Hydrogen Bond: A weak interaction between a hydrogen atom (partially positive) and an electronegative atom (such as oxygen or nitrogen) of another molecule.

Table: Comparison of Chemical Bonds

Ions and Ion Formation

Atoms can gain or lose electrons to form ions, which are charged particles important in physiological processes.

• Cation: An atom that loses an electron and becomes positively charged.

• Anion: An atom that gains an electron and becomes negatively charged.

Example: Sodium (Na) loses one electron to become Na+ (cation); Chlorine (Cl) gains one electron to become Cl- (anion).

Chemical Reactions in the Body

Types of Chemical Reactions

Chemical reactions are essential for life, enabling metabolism and other physiological functions. The main types include:

• Synthesis Reaction: Two or more substances combine to form a more complex product.

• Decomposition Reaction: A complex substance breaks down into simpler components.

• Exchange Reaction: Parts of molecules are exchanged to form new substances.

Example: The formation of water from hydrogen and oxygen is a synthesis reaction:

Summary of Key Terms

• Atom: The smallest unit of an element, retaining its chemical properties.

• Element: A substance made of only one kind of atom.

• Molecule: Two or more atoms bonded together.

• Compound: A molecule containing atoms of different elements.

Additional info:

• These concepts form the foundation for understanding physiological processes such as nerve impulse transmission, muscle contraction, and cellular metabolism.

• Knowledge of chemical bonds and reactions is essential for interpreting biochemical pathways in anatomy and physiology.