Atoms, Molecules, and the Basis of Life: Study Notes for General Biology

Topic 1: Defining Life

What Does It Mean to Be Alive?

Understanding what constitutes a living organism is a foundational concept in biology. Scientists use several criteria to distinguish living things from non-living things.

• Living organisms exhibit characteristics such as metabolism, growth, response to stimuli, reproduction, and cellular organization.

• Non-living things do not possess these characteristics.

• Examples of living things: plants, animals, bacteria, fungi.

• Examples of non-living things: rocks, water, air.

Application: When presented with images (e.g., tree bark, sand, microorganisms), use the criteria above to determine if the subject is alive.

Topic 2: Atoms and Molecules

Atoms: The Building Blocks of Matter

All matter, living and non-living, is composed of atoms. Atoms are the smallest units of an element that retain the properties of that element.

• Atom: The basic unit of matter, consisting of a nucleus (protons and neutrons) and electrons.

• Element: A substance made of only one kind of atom.

• Molecule: Two or more atoms bonded together.

• Compound: A molecule that contains atoms of different elements.

Example: Water (H2O) is a compound made of hydrogen and oxygen atoms.

Atomic Structure

The structure of an atom determines its chemical properties and interactions.

• Nucleus: Central part of the atom containing protons and neutrons.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

Bohr Model: A simplified representation of the atom showing electrons in defined energy levels around the nucleus.

Atomic Number and Atomic Mass

Each element is defined by its atomic number and atomic mass.

• Atomic Number (Z): Number of protons in the nucleus; determines the element.

• Atomic Mass (A): Total number of protons and neutrons in the nucleus.

Formulas:

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

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

Example: Helium (He) has 2 protons and 2 neutrons. Atomic number = 2, atomic mass = 4.

Subatomic Particles: Properties and Comparison

Atoms are made of three main subatomic particles, each with distinct properties.

Particle	Symbol	Charge	Mass (Da)	Mass Number
Proton	p	+1	1.6726 × 10-24	1
Neutron	n	0	1.6749 × 10-24	1
Electron	e	-1	9.1094 × 10-28	0

Note: The mass of electrons is negligible compared to protons and neutrons.

Periodic Table: Element Symbols and Information

The periodic table provides key information about each element, including its atomic number, symbol, and atomic mass.

• Element Symbol: One or two-letter abbreviation for the element (e.g., He for Helium).

• Atomic Number: Shown above the symbol; identifies the element.

• Atomic Mass: Shown below the symbol; average mass of all isotopes.

Example: Zinc (Zn) has atomic number 30 and atomic mass 65.38.

Calculating Neutrons and Protons

To determine the number of neutrons in an atom:

• Number of Neutrons = Atomic Mass - Atomic Number

Example: Silver (Ag) has atomic number 47 and atomic mass 107.8682. Number of neutrons ≈ 108 - 47 = 61.

Topic 3: Chemical Interactions and Molecule Formation

Atoms Form Molecules Through Chemical Bonds

Atoms interact to form molecules by sharing or transferring electrons, resulting in chemical bonds.

• Covalent Bond: Atoms share electrons to fill their outermost shell.

• Ionic Bond: Atoms transfer electrons, resulting in charged ions that attract each other.

• Octet Rule: Atoms tend to form bonds to achieve eight electrons in their outer shell (except for hydrogen and helium).

Example: Water (H2O) forms when hydrogen and oxygen share electrons.

Types of Chemical Interactions

Chemical interactions are essential for the structure and function of biological molecules.

• Covalent Bonds: Strong bonds formed by sharing electrons.

• Ionic Bonds: Bonds formed by the attraction between oppositely charged ions.

• Hydrogen Bonds: Weak bonds important in the structure of water and biological macromolecules.

Application: Understanding chemical interactions helps explain the properties of water, proteins, DNA, and other biological molecules.

Summary Table: Atomic Structure and Properties

Term	Definition	Example
Atom	Smallest unit of an element	Helium atom
Element	Substance made of one type of atom	Oxygen (O)
Molecule	Two or more atoms bonded together	Water (H2O)
Compound	Molecule with different elements	Carbon dioxide (CO2)

Practice Questions (iClicker Examples)

• Is it alive? (Images of various objects and organisms)

• What is the basic "unit" of all life? (Answer: Cells)

• What is the basic "unit" of all matter? (Answer: Atoms)

• Which diagram depicts the Bohr model for an atom?

• Label the parts of an atom (proton, neutron, electron, nucleus).

• What is the atomic number/mass of a given element?

• How many neutrons/protons does an atom possess?

Additional info: These notes expand on the brief points and images in the original slides, providing definitions, examples, and context suitable for introductory college biology students.