Atomic Structure and Chemistry Basics

What is an Element?

• An element is a substance that consists of only one type of atom.
• The human body is composed of elements that constitute over 95% of its atoms, including oxygen, carbon, hydrogen, nitrogen, and calcium.

Atom, Element, and Molecule

• An atom is the smallest unit of a chemical element.
• An element is a substance that consists of only one type of atom.
• A molecule is a group of two or more atoms that are chemically bonded together.

Structure of an Atom

• An atom is composed of three particles: protons, neutrons, and electrons.
• Protons have a positive charge, neutrons have no charge, and electrons have a negative charge.
• Protons and neutrons are found in the nucleus of the atom, while electrons orbit around the nucleus.
• The mass of an atom is determined by the number of protons and neutrons in the nucleus.
• The charge of an atom is determined by the number of electrons.

Atomic Number and Ions

• The atomic number of an atom describes the number of protons in the nucleus.
• Changing the atomic number changes the type of atom.
• An ion is an atom that has gained or lost electrons, resulting in a positive or negative charge.

Isotopes and Octet Rule

• Isotopes are atoms of the same element that have different numbers of neutrons.
• The octet rule states that atoms tend to gain or lose electrons to achieve a full outer energy level of eight electrons.
• The octet rule helps to determine the formation of chemical bonds.

Valence Electrons and Covalent Bonds

• Valence electrons are the electrons in the outermost energy level of an atom.
• Valence electrons are important in the formation of chemical bonds.
• A covalent bond is a chemical bond that forms when two or more atoms share valence electrons.
• There are two types of covalent bonds: polar and nonpolar.

Hydrogen Bonds

• A hydrogen bond is a weak type of chemical bond that forms between atoms with a hydrogen atom bonded to a highly electronegative atom.
• Hydrogen bonds are weaker than covalent bonds.
• In a sample of water, covalent bonds would be found between oxygen and hydrogen atoms, while hydrogen bonds would be found between water molecules.

Solutes, Solvents, and Solutions

• A solute is a substance that is dissolved in a solvent.
• A solvent is a substance that is able to dissolve other substances.
• A solution is a mixture of a solute and a solvent.
• Hydrophobic substances are nonpolar and tend to repel water, while hydrophilic substances are polar and tend to attract water.

Energy and Chemical Reactions

• Potential energy is the energy stored in a system, while kinetic energy is the energy of motion.
• Chemical bonds represent a form of potential energy.
• Catabolic reactions are reactions that release energy, while anabolic reactions are reactions that require energy.
• Enzymes are proteins that catalyze chemical reactions, increasing the rate of the reaction.

Enzymes

• An enzyme active site is the region of the enzyme where the substrate binds.
• Enzymes increase the rate of a chemical reaction by lowering the activation energy.
• Factors that can affect an enzyme's ability to catalyze a chemical reaction include temperature, pH, and substrate concentration.

Acids and Bases

• An acid is a substance that donates a proton, while a base is a substance that accepts a proton.
• pH is a measure of the concentration of hydrogen ions in a solution.
• A lower pH level indicates a higher concentration of hydrogen ions.

Organic Molecules

• An organic molecule is a molecule that contains carbon and hydrogen atoms.
• The four classes of organic molecules are carbohydrates, proteins, lipids, and nucleic acids.
• A monomer is a small molecule that can be linked together to form a polymer.
• A polymer is a large molecule composed of many monomers.

Carbohydrates

• The generalized chemical formula for a carbohydrate is C₆H₁₂O₆.
• Carbohydrates serve as energy sources and structural components in the human body.
• Examples of carbohydrates include monosaccharides (glucose), disaccharides (sucrose), and polysaccharides (starch).

Amino Acids

• An amino acid is a molecule that contains a carboxyl group and an amino group.
• The generalized structure of an amino acid is R-CH(NH₂)-COOH.
• Examples of amino acids include glycine, alanine, and serine.

Nucleic Acids

• A single subunit of a nucleic acid is called a nucleotide.
• The generalized structure of a nucleotide is a sugar molecule, a phosphate group, and a nitrogenous base.
• Examples of nucleic acids include DNA and RNA.
• Nucleic acids serve as genetic material and play a role in protein synthesis.

Lipids

• Lipids are molecules that contain carbon and hydrogen atoms, but are insoluble in water.
• The presence of nonpolar bonds gives lipids their characteristic insolubility.
• Examples of lipids include triglycerides and phospholipids.
• Lipids serve as energy sources and structural components in the human body.