Chemistry Comes Alive: Foundations of Matter, Energy, and Atomic Structure

The Chemical World

Introduction to Chemistry

Chemistry is essential for understanding biological processes, especially physiology. It explores the nature of matter and energy, which are fundamental to all living and non-living things.

• Matter: Any substance in the universe that has mass and occupies space. Matter exists in three states: solid, liquid, and gas. All matter is composed of atoms.

• Energy: The capacity to do work or put matter into motion. Energy exists in two main forms: kinetic energy (energy in motion) and potential energy (stored energy).

Matter and Energy

Forms and Conservation of Energy

Energy can be transformed between kinetic and potential forms but cannot be created or destroyed (Law of Conservation of Energy).

• Kinetic Energy: Energy of moving objects (e.g., moving atoms, swinging door).

• Potential Energy: Stored energy (e.g., water behind a dam, ball at the top of a hill).

• Chemical Energy: Stored in chemical bonds, released during chemical reactions (e.g., ATP in cells).

• Electrical Energy: Movement of charged particles (e.g., nerve impulses).

• Mechanical Energy: Direct movement of matter (e.g., pushing a door).

• Radiant/Electromagnetic Energy: Energy traveling in waves (e.g., microwaves, ultraviolet light).

Atoms and Elements

Elements and Atomic Structure

An element is a pure substance made of one type of atom. Atoms are the smallest units retaining the properties of an element. There are 92 naturally occurring elements (118 total), organized in the Periodic Table. Four elements—carbon (C), hydrogen (H), nitrogen (N), and oxygen (O)—make up 96% of the body weight of organisms.

• Atom: Composed of a nucleus (protons and neutrons) and orbitals (electrons).

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles in orbitals around the nucleus.

Atomic Number and Mass

• Atomic Number: Number of protons in the nucleus; defines the element and does not change.

• Atomic Mass (Mass Number): Number of protons plus neutrons in the nucleus. Electrons have negligible mass.

• Calculating Neutrons: $\text{Number of neutrons} = \text{Atomic mass} - \text{Atomic number}$ Example for Sodium (Na): $23 - 11 = 12$ neutrons.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons. Most elements exist as mixtures of isotopes. For example, C-12 and C-14 are isotopes of carbon.

Molecules and Compounds

Definitions and Types

• Molecule: Two or more atoms held together by chemical bonds (e.g., O2, H2).

• Compound: Two or more different atoms bonded together (e.g., H2O, CH4).

• Mixture: Two or more substances physically intermixed. Types include solutions, colloids, and suspensions.

Types of Mixtures

Solution	Colloid	Suspension
Homogeneous mixture; solute particles are very small and do not settle out (e.g., salt water).	Heterogeneous mixture; particles are larger than in a solution but do not settle out (e.g., milk).	Heterogeneous mixture; particles are large and will settle out over time (e.g., sand in water).

Chemical Bonding

Electron Shells and Stability

• Electrons occupy shells (energy levels) around the nucleus. Shell 1 holds 2 electrons, shell 2 holds up to 8, shell 3 up to 8.

• Octet Rule: Atoms are most stable when their outermost shell is full (usually 8 electrons).

Types of Chemical Bonds

• Ionic Bonds: Electrons are transferred from one atom to another, forming ions (charged atoms).

• Covalent Bonds: Electrons are shared between atoms, creating stable molecules.

• Hydrogen Bonds: Weak attractions between polar molecules, important in water and biological molecules.

Electron Arrangement and Reactivity

Valence Shells and Chemical Activity

• Atoms with incomplete valence shells are more reactive and tend to gain, lose, or share electrons to achieve stability.

• Chemically inert elements (e.g., helium, neon) have full valence shells and are not reactive.

• Chemically reactive elements have space in their valence shell for additional electrons.

Summary Table: Atomic Properties

Element	Atomic Number	Most Common Mass Number
Hydrogen	1	1
Carbon	6	12
Nitrogen	7	14
Oxygen	8	16
Sodium	11	23
Iron	26	56

Practice Questions

• What is the atomic number of Fluorine?

• How many protons, neutrons, and electrons does Fluorine have?

Additional info: These notes are based on introductory chemistry concepts, including atomic structure, elements, energy forms, and chemical bonding, suitable for college-level students.