Atoms, Elements, and Atomic Structure: Foundations for Anatomy & Physiology

Introduction to Matter and Chemical Elements

Definition of Matter

Matter is anything that occupies space and has mass. All living and non-living things are composed of matter, including organisms, rocks, oceans, and air.

• Matter: Anything that takes up space and has mass.

• All matter consists of at least one chemical element.

Chemical Elements

Chemical elements are pure substances made of only one type of atom. They are the fundamental building blocks of matter.

• Atom: The smallest unit of matter that retains the properties of an element.

• Atoms make up both elements and compounds.

Examples of Atoms in Matter

• Diamond: Composed of carbon atoms.

• Honey Bee: Contains atoms such as carbon, hydrogen, and oxygen.

• Glucose Structure: Made of carbon, hydrogen, and oxygen atoms.

Atomic Structure

Subatomic Particles

Atoms are made of subatomic particles, each with a characteristic charge, mass, and location within the atom.

Subatomic Particle	Electric Charge	Atomic Mass Unit (AMU)	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	-1	~0	Orbiting Nucleus

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

Elements of Life

Essential Elements

Of all known elements, only a small subset is found in living organisms. The periodic table arranges all known elements based on their chemical properties.

• Approximately 97% of the mass of most life is composed of Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorus (P), and Sulfur (S) (CHNOPS).

• Trace elements are required for life in small amounts.

Periodic Table of Elements

The periodic table organizes elements by increasing atomic number and groups elements with similar chemical properties.

Atomic Properties

Atomic Number and Mass Number

Each atom of an element has unique properties:

• Atomic Number: Number of protons in the nucleus (unique for each element).

• Mass Number: Sum of protons and neutrons in the nucleus.

• Atomic Mass: Average mass of all atoms of an element.

Formula:

• Atomic Number: $\text{Number of Protons}$

• Mass Number: $\text{Number of Protons} + \text{Number of Neutrons}$

Example: Atomic Properties of Carbon

• Carbon has 6 protons (atomic number 6).

• Mass number can vary due to different numbers of neutrons (isotopes).

Electron Orbitals & Energy Shells

Electron Arrangement

Electrons are arranged around the nucleus in energy shells or orbitals.

• Shells closer to the nucleus are lower in energy; shells farther away are higher in energy.

• Valence electrons: Electrons found in the outermost energy shell.

• First shell holds up to 2 electrons; second shell holds up to 8 electrons.

Example: Energy Shells for CHNOPS Elements

Element	Atomic Number	Valence Electrons
Carbon (C)	6	4
Hydrogen (H)	1	1
Nitrogen (N)	7	5
Oxygen (O)	8	6
Phosphorus (P)	15	5
Sulfur (S)	16	6

Octet Rule

Stability of Atoms

Atoms are more stable (less reactive) when their valence shells are fully occupied.

• First energy shell holds up to 2 electrons.

• Second energy shell holds up to 8 electrons.

• Atoms are reactive when their outer valence shells are not full.

Example: Electron Distribution in Nitrogen

• Nitrogen (atomic number 7): 2 electrons in the first shell, 5 in the second shell.

Isotopes and Atomic Mass

Definition of Isotopes

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

• Atomic Number: Number of protons (same for all isotopes of an element).

• Mass Number: Number of protons plus neutrons (varies among isotopes).

• Atomic Mass: Weighted average of all isotopes of an element.

Example: Isotopes of Carbon

Isotope	Protons	Neutrons	Electrons
Carbon-12	6	6	6
Carbon-13	6	7	6
Carbon-14	6	8	6

Radioactive Isotopes

Definition and Applications

Radioactive isotopes are unstable isotopes that break down and emit energy in the form of rays or particles.

• Half-life: Time it takes for half of the radioactive atoms in a sample to break down.

• Used in medicine, fossil dating, and cancer treatment.

Example: Radioactivity of Carbon-14

• Carbon-14 decays over time, releasing particles and energy.

• Used for dating fossils and archaeological samples.

Key Terms and Concepts

• Atom: Smallest unit of matter.

• Element: Pure substance made of one type of atom.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Number of protons plus neutrons.

• Valence Electrons: Electrons in the outermost shell.

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

• Radioactive Isotope: Unstable isotope that emits energy as it decays.

Summary Table: Atomic Structure and Properties

Property	Description
Atomic Number	Number of protons in nucleus
Mass Number	Number of protons + neutrons
Isotope	Same element, different number of neutrons
Valence Electrons	Electrons in outermost shell
Octet Rule	Stability with 8 electrons in valence shell
Radioactive Isotope	Unstable, emits energy as it decays

Applications in Anatomy & Physiology

• Understanding atomic structure is essential for studying molecules and chemical reactions in the human body.

• Radioactive isotopes are used in medical imaging and treatment.

• Elements like CHNOPS are fundamental for the structure and function of biomolecules.

Additional info: These notes provide foundational chemistry concepts that are directly relevant to Anatomy & Physiology, especially for understanding biomolecules, cellular processes, and medical applications.