Learning Outcomes:

After this lesson, you should be able to:

• Distinguish between elements and atoms, and state the four most abundant elements in the body.
• Name the subatomic particles of an atom, and indicate their mass, charge, and location in an atom.
• Define atomic number, mass number, isotope, atomic mass, and mole.

An element is the simplest type of matter, having unique chemical properties. About 96% of the body’s weight result from the elements oxygen, carbon, hydrogen, and nitrogen. The majority of the body’s weight is from oxygen.

Many elements are present in only trace amounts, but still play essential roles in the body. Elements can have multiple roles and exist in different states in the body.

An atom is the smallest particle of an element that has the chemical properties of that element. Atoms are tiny and are composed of smaller parts called subatomic particles.

Atomic Structure

Subatomic Particles – there are three basic particles

• Protons:
  • small particle inside the nucleus of an atom that carries a positive charge (p⁺)
• Neutrons:
  • just slightly larger particles inside the nucleus of an atom, have not charge (n⁰)
• Electrons:
  • tiny particles that orbit around the nucleus of an atom that carry a negative charge (e^-)

The number of positively charged protons in an atom equals the number of negatively charged protons. Because of this, all atoms are electrically neutral, meaning an atom as a whole has no charge.

Atomic Number and Mass Number

The atomic number of an element is equal to the number of protons in the nucleus of an atom. The number of electrons is equal to the number of protons, the atomic number is also the number of electrons.

Protons and neutrons have about the same mass, and they are responsible for the mass of an atoms. The mass number of an element is the number of protons plus the number of neutrons.