Matter, Energy & Bonds

Introduction

Understanding the basic principles of matter, atomic structure, and chemical bonding is essential for studying Anatomy & Physiology. These concepts explain how biological molecules form and interact, which underpins all physiological processes.

Atoms, Subatomic Particles, and Atomic Structure

Electrons, Protons & Neutrons

Atoms are the smallest units of matter that retain the properties of an element. They are composed of three main subatomic particles:

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also found in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron shells.

The number of protons defines the atomic number and the identity of the element.

Atomic Number vs. Mass Number

• Atomic Number: The number of protons in the nucleus of an atom. It determines the element's identity (e.g., Hydrogen has 1 proton, so atomic number = 1).

• Mass Number: The sum of protons and neutrons in the nucleus. Electrons have negligible mass.

Formula:

Summary Table: Subatomic Particles

Electron Shells and Atomic Structure

Electrons occupy specific regions called electron shells around the nucleus. Each shell can hold a certain number of electrons:

• 1st shell: Up to 2 electrons

• 2nd shell: Up to 8 electrons

• 3rd shell: Up to 8 electrons (satisfied with 8, known as the Octet Rule)

Atoms may have more than three shells, but the first three are most relevant for biological molecules.

Atoms vs. Elements & Major Elements in the Body

Atoms and Elements

An atom is the smallest unit of an element that retains its chemical properties. An element is a substance made entirely of one kind of atom. For example, a water molecule (H2O) is composed of hydrogen and oxygen atoms, each with unique properties.

• Atoms: Individual units with unique chemical properties.

• Elements: Pure substances consisting of only one type of atom.

Example: Oxygen and hydrogen are elements; their atoms combine to form water, a compound with new properties.

Major Elements in the Human Body

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

These four elements make up over 96% of the human body's mass.

Isotopes and Radioisotopes

Definitions and Properties

• Isotopes: Atoms of the same element with different numbers of neutrons, resulting in different mass numbers.

• Radioisotopes: Unstable isotopes that decay over time, emitting radiation.

Isotopes behave the same chemically but may differ physically due to mass. Radioisotopes are used in medical imaging and treatment.

Applications of Radioisotopes

• Radiation therapy: Destroys cancer cells by damaging their structure.

• Tracers: Used in diagnostic imaging to track organ function.

• Treatment of thyroid disorders: Iodine-131 is used to treat overactive or cancerous thyroid tissue.

Examples of Medical Radioisotopes:

Mixtures: Solutions, Solvents, Colloids & Suspensions

Definitions and Differences

• Solution: Homogeneous mixture of two or more components; solute particles are very small and evenly distributed. Example: Salt dissolved in water.

• Solvent: The substance that dissolves the solute (usually water in biological systems).

• Colloid: Mixture with small, evenly distributed particles that do not settle out. Example: Cytoplasm in cells.

• Suspension: Mixture with large, unevenly distributed particles that will settle out over time. Example: Blood cells in plasma.

Table: Comparison of Mixture Types

Valence Shells and Chemical Reactivity

Role of Valence Electrons

The valence shell is the outermost electron shell of an atom. The number of electrons in this shell determines an atom's chemical reactivity.

• Octet Rule: Atoms are most stable when they have 8 electrons in their valence shell.

• Duet Rule: Atoms with 5 or fewer electrons are stable with 2 electrons in their valence shell.

Atoms will gain, lose, or share electrons to achieve stability, forming chemical bonds.

Ions and Electrolytes

Definitions

• Ion: An atom or molecule with a net electric charge due to unequal numbers of protons and electrons.

• Cation: Positively charged ion (more protons than electrons).

• Anion: Negatively charged ion (more electrons than protons).

• Electrolyte: Substance that ionizes in water and can conduct electricity (e.g., salts, acids, bases).

Example: Sodium ion (Na+) and chloride ion (Cl-) in table salt.

Chemical Bonds: Types and Biological Examples

Types of Chemical Bonds

• Ionic Bonds: Formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions that attract each other. Example: NaCl (table salt).

• Non-polar Covalent Bonds: Electrons are shared equally between atoms. Example: O2 molecule.

• Polar Covalent Bonds: Electrons are shared unequally, creating partial charges (poles) on the molecule. Example: H2O (water).

• Hydrogen Bonds: Weak attractions between polar molecules, often involving hydrogen. Example: Bonds between water molecules or within proteins.

• Van der Waals Forces: Weak attractions due to temporary polarization in nonpolar molecules.

Table: Comparison of Chemical Bonds

Summary

• Atoms, elements, and chemical bonds are foundational to understanding biological molecules and physiological processes.

• Major elements in the body include oxygen, carbon, hydrogen, and nitrogen.

• Isotopes and radioisotopes have important medical applications.

• Mixtures in the body can be solutions, colloids, or suspensions, each with distinct properties.

• Valence electrons determine chemical reactivity and the formation of ions and bonds.