Chemistry is the study of the composition and structure of substances and the reactions they undergo.

Basic Chemistry

Matter, Mass, and Weight

• Matter is anything that occupies space.
• Mass is the amount of matter in an object, and weight results from the gravitational attraction between earth and matter.

Elements and Atoms

• An element is the simplest type of matter with unique chemical and physical properties.
• An atom is the smallest particle of an element that has the chemical characteristics of that element. An element is composed of only one kind of atom.

Atomic Structure

• Atoms consist of neutrons, positively charged protons, and negatively charged electrons.
• Atoms are electrically neutral because the number of protons in atoms equals the number of electrons.
• Protons and neutrons are found in the nucleus, and electrons are located around the nucleus, which can be represented by an electron cloud.
• The atomic number is the number of protons in an element.

Electrons and Chemical Bonding

• Ionic bonding results when an electron is transferred from one atom to another.
• Covalent bonding results when a pair of electrons are shared between atoms. A polar covalent bond is an unequal sharing of electron pairs.

Hydrogen Bonds

• A hydrogen bond is the weak attraction that occurs between the oppositely charged regions of polar molecules. Hydrogen bonds are important in determining the three-dimensional structure of large molecules.

Molecules and Compounds

• A molecule is two or more atoms chemically combined to form a structure that behaves as an independent unit.
• A compound is two or more different types of atoms chemically combined. A compound can be a molecule (covalent compound) or an organized array of ions (ionic compound).

Dissociation

• Dissociation is the separation of ions in an ionic compound by polar water molecules.

Chemical Reactions

Classification of Chemical Reactions

• A synthesis reaction is the combination of reactants to form a new, larger product.
• A decomposition reaction is the breakdown of larger reactants into smaller products.
• An exchange reaction is a decomposition reaction, in which reactants are broken down, and a synthesis reaction, in which the products of the decomposition reaction combine.

Reversible Reactions

• In a reversible reaction, the reactants can form products, or the products can form reactants.
• The amount of reactants relative to products is constant at equilibrium.

Energy and Chemical Reactions

• Energy is the capacity to do work. Potential energy is stored energy that could do work, and kinetic energy does work by causing the movement of an object.
• Energy can be neither created or destroyed, but one type of energy can be changed into another.
• Energy exists in chemical bonds as potential energy.
• Energy is released in chemical reactions when the products contain less potential energy than the reactants. The energy can be lost as heat, be used to synthesize molecules, or can do work.
• Energy is absorbed in reactions when the products contain more potential energy than the reactants.

Rate of Chemical Reactions

• The rate of chemical reactions increases when the concentration of the reactants increases, temperature increases, or a catalyst is present.
• A catalyst (enzyme) increases the rate of chemical reactions without being altered permanently.

Acids and Bases

• Acids are proton (hydrogen ion) donors, and bases are proton acceptors.

The pH Scale

• A neutral solution has an equal number of hydrogen ions and hydroxide ions and a pH of 7.0.
• An acidic solution has more hydrogen ions than hydroxide ions and a pH of less than 7.0.
• A basic solution has fewer hydrogen ions than hydroxide ions and a pH greater than 7.0.

Salts

• A salt is formed when an acid reacts with a base.

Buffers

• Buffers are chemicals that resist changes in pH when acids or bases are added.

Inorganic Chemistry

• Inorganic chemistry is mostly concerned with noncarbon-containing substances, but does include such carbon-containing substances as carbon dioxide and carbon monoxide.

Oxygen and Carbon Dioxide

• Oxygen is involved with the extraction of energy from food molecules.
• Carbon dioxide is a by-product of the breakdown of food molecules.

Water

• Water stabilizes body temperature, provides protection by acting as a lubricant or cushion, is necessary for many chemical reactions, and transports many substances.

Organic Chemistry

• Organic molecules contain carbon atoms bound together by covalent bonds.

Carbohydrates

• Carbohydrates provide the body with energy.
• Monosaccharides are the building blocks that form more complex carbohydrates, such as disaccharides and polysaccharides.

Lipids

• Lipids provide energy (fats), are structural components (phospholipids), and regulate physiological processes (steroids).
• The building blocks of triacylglycerols (fats) are glycerol and fatty acids.

Proteins

• Proteins regulate chemical reactions (enzymes), are structural components, and cause muscle contraction.
• The building blocks of proteins are amino acids.
• Denaturation of proteins disrupts hydrogen bonds, which changes the shape of proteins and makes them nonfunctional.
• Enzymes are specific, bind to reactants according to the lock-and-key model, and function by lowering activation energy.

Nucleic Acids

• Nucleic acids include DNA, the genetic material, and RNA, which is involved in protein synthesis.
• The building blocks of nucleic acids are nucleotides, which consist of a sugar (deoxyribose or ribose), a nitrogen base, and a phosphate group.>>