Part 1—Basic Chemistry

2.1 Matter and Energy

This section introduces the foundational concepts of matter and energy, which are essential for understanding chemical processes in the human body.

• Matter: Anything that has mass and occupies space.

  • Can be seen, smelled, and/or felt.

  • Weight is mass plus the effects of gravity.

  • States of matter:

    • Solid: Definite shape and volume.

    • Liquid: Changeable shape; definite volume.

    • Gas: Changeable shape and volume.

• Energy: The capacity to do work or put matter into motion.

  • The greater the work done, the more energy is used up.

  • Exists in two main forms:

    • Kinetic energy: Energy in action.

    • Potential energy: Stored (inactive) energy.

  • Energy can be transformed from potential to kinetic energy.

Forms of Energy

• Chemical energy: Stored in bonds of chemical substances.

• Electrical energy: Results from movement of charged particles.

• Mechanical energy: Directly involved in moving matter.

• Radiant (electromagnetic) energy: Travels in waves (e.g., heat, visible light, ultraviolet light, X-rays).

Energy Form Conversions

• Energy may be converted from one form to another (e.g., electrical energy to light energy in a lamp).

• Energy conversion is inefficient; some energy is "lost" as heat, which is partly unusable.

2.2 Atoms and Elements

This section covers the basic building blocks of matter: elements and atoms, and their relevance to the human body.

• Chemical element: A substance that cannot be broken down into simpler substances by ordinary chemical methods.

• Four elements make up about 96% of body mass:

  • Carbon (C)

  • Oxygen (O)

  • Hydrogen (H)

  • Nitrogen (N)

• Other elements are present in trace amounts.

• The periodic table lists all known elements (currently 118, with 92 occurring in nature).

Table: Common Elements Composing the Human Body

Additional info: Trace elements such as chromium, cobalt, copper, fluorine, manganese, molybdenum, selenium, silicon, tin, vanadium, and zinc are required in very minute amounts for enzyme activity and other specialized functions.

2.2 Atoms and Elements (continued)

• Atoms: Unique building blocks for each element; smallest particles with properties of that element.

• Atomic symbol: One- or two-letter shorthand for each element (e.g., O for oxygen, C for carbon).

Structure of Atoms

• Composed of three subatomic particles:

  • Protons: Positive charge (+), mass = 1 amu.

  • Neutrons: No charge (0), mass = 1 amu.

  • Electrons: Negative charge (–), virtually no mass (0 amu).

• Protons and neutrons are located in the nucleus; electrons orbit around the nucleus.

• Number of protons equals number of electrons in a neutral atom.

Atomic Models

• Planetary model: Electrons move in fixed circular paths (useful for illustrations).

• Orbital model: Electrons are found in regions of space (orbitals) where they are most likely to be located.

Identifying Elements

• Atomic number: Number of protons in the nucleus. Written as subscript to the left of the atomic symbol (e.g., H for hydrogen).

• Mass number: Total number of protons and neutrons in the nucleus. Written as superscript to the left of the atomic symbol (e.g., H for deuterium).

• Isotopes: Structural variations of the same element; same number of protons, different number of neutrons.

• Atomic weight: Average of mass numbers of all isotope forms of an atom.

Radioisotopes

• Isotopes that decompose to more stable forms, releasing energy (radioactivity).

• Used in biological research and medicine (e.g., diagnostic imaging, cancer treatment).

• Some radioisotopes can damage living tissue; others are used to destroy localized cancers.

Key Equations

• Atomic number:

• Mass number:

Example

• Hydrogen: 1 proton, 0 neutrons, 1 electron.

• Deuterium (isotope of hydrogen): 1 proton, 1 neutron, 1 electron.

• Tritium (radioisotope of hydrogen): 1 proton, 2 neutrons, 1 electron.