What are Molecules?

Molecules

• Molecules are formed when two or more atoms combine and become chemically bonded.
• Atoms of the same or different elements can bond to form molecules, such as O2 (oxygen) or H2O (water).
• Molecules are the building blocks of everything in the world, living and nonliving.

Characteristics of Living Organisms

• Eight criteria must be met to be considered a living organism: growth and development, evolution, response to the environment, comprised of cells, reproduction, genetic code, homeostasis, and obtaining and using energy.
• Living organisms range in size, from bacteria to blue whales, but all meet the above criteria.

Size of Molecules

• Molecules come in different shapes and sizes, making it difficult to determine their size.
• Molecular weight is used to measure the size of molecules, which is the sum of the mass of all atoms present within a molecule.
• Metric units such as nanometers (nm) and angstroms (Å) can also be used to measure molecules.
• 1 nm is equal to one billionth of a meter, and 1 Å is equal to one ten-billionth of a meter.
• Examples of molecular sizes: water molecule (0.27 nm), carbon atom (0.34 nm), coffee bean (96,000,000 nm), grain of rice (20,000,000 nm), and red blood cell (8,000 nm).

Types of Molecules

• Homonuclear diatomic molecules: bonding of two identical atoms, such as O2, H2, N2, F2, I2, Cl2, and Br2.
• Heteronuclear diatomic molecules: bonding of two different atoms, such as NaCl, HCl, CO, and NO.

Molecules in Living Things

• Water is the most abundant molecule in the human body, making up about 65% of its total mass.
• Common elements making up the human body include carbon, nitrogen, hydrogen, oxygen, and sulfur.
• Macromolecules in the body include proteins, lipids, carbohydrates, and nucleic acids.
• Proteins are the largest macromolecule, making up 20% of body weight, and are composed of carbon, hydrogen, oxygen, nitrogen, and sulfur.
• Carbohydrates are used for quick energy and are composed of carbon, hydrogen, and oxygen.
• Lipids are used to store energy and are composed of carbon, hydrogen, and oxygen.
• Nucleic acids (DNA and RNA) are responsible for storing and expressing genetic information and are composed of carbon, hydrogen, oxygen, phosphorus, and nitrogen.

Learn about the basics of molecules, including how atoms combine to form chemical bonds and create different types of molecules such as O2 and H2O.