Chapter 2: The Chemistry of Life

Atoms are the basic unit of matter and are made up of protons, neutrons, and electrons
Protons and neutrons have the same mass but different charges * Protons have a positive charge (+) * Neutrons carry no charge at all
An electron is a negatively charged particle (-)
The nucleus is the center of the atom

An element is a pure substance that consists entirely of one type of atom * Each element has a one- or two-letter symbol (C for carbon or Na for sodium) * An element’s atomic number is the number of protons in the atom
Atoms of the same element that have different numbers of neutrons are isotopes * Protons + neutrons = mass number * Isotopes are named using their mass number * Some isotopes are radioactive

A compound is a substance formed by the chemical combination of two or more elements in definite proportions * The number of each element in a compound can be shown using chemical formulas * Ex: Since water has 2 atoms of hydrogen and 1 atom of oxygen, the chemical formula for water is H2O

@@The 2 main chemical bonds are ionic and covalent bonds@@ * An ionic bond is formed when one or more electrons are transferred from one atom to another * An atom that loses electrons becomes positively charged, while an atom that gains electrons has a negative charge * Oppositely charged ions attract one another * A covalent bond is a bond between atoms in which the electrons are shared and is formed when the electrons travel around the nuclei of both atoms * Single covalent bond: atoms sharing 2 electrons * Double bond: atoms sharing 4 electrons * Triple bond: atoms sharing 6 electrons * @@Covalent bonds form structures called molecules@@ * The molecule is the smallest unit of most compounds that displays all properties of that compound * In a water molecule, each hydrogen atom shares 2 electrons with the oxygen atom. So, each hydrogen atom is joined to the oxygen atom by a covalent bond.

@@Water is a polar molecule@@ * A molecule in which the charges are unevenly spread out is said to be “polar”
The pull between a partially positive hydrogen atom on one molecule and a partially negative oxygen atom on another is known as a hydrogen bond * @@Hydrogen bonds give water special properties such as cohesion, adhesion, and a high heat capacity@@ * Cohesion: the attraction between molecules of the same substance * Adhesion: the force of attraction between different kinds of molecules * Heat capacity: the amount of energy needed to increase a substance’s temperature

Water is often part of a mixture * A mixture is made up of elements or compounds that are combined but not bonded together
Two kinds of mixtures made with water are solutions and suspensions * A solution is a type of mixture in which all the components are evenly distributed. Contains one or more solutes in a solvent * A solute is what is dissolved * A solvent is what does the dissolving * A suspension is a mixture of water and non-dissolved material

The pH scale is used to show the concentration of H+ ions in a solution * The scale ranges from 0 to 14 * A solution with a pH of 7 is considered neutral * Solutions with a pH below 7 are acidic * Solutions with a pH above 7 are basic
An acid is a compound that releases hydrogen ions in a solution; has a pH of less than 7
A base is a compound that releases hydroxide ions in a solution; has a pH of more than 7
A buffer is a compound that prevents sharp, sudden changes in pH

Carbon atoms have 4 electrons available for bonding, including @@hydrogen, oxygen, phosphorus, sulfur, and nitrogen@@ to form life’s molecules
Carbon atoms can bond with one another * Carbon-carbon bonds can be single, double, or triple and can even close up on themselves to form rings

Macromolecules are made from thousands or even hundreds of thousands of smaller molecules called monomers * Monomers join to form polymers
The four major groups of macromolecules are: * Carbohydrates: compounds made up of carbon, hydrogen, and oxygen atoms; a type of nutrient that is the main source of energy for the body * Simple sugars such as monosaccharides and disaccharides * Complex carbohydrates are the large macromolecules formed when simple sugars join together * Lipids: macromolecules that generally do not dissolve in water and are made mostly of carbon and hydrogen atoms; used to store energy and are parts of membranes and waterproof coverings * Common lipids include fats, oils, and waxes * Saturated and unsaturated * Nucleic acids: macromolecules containing hydrogen, oxygen, nitrogen, carbon, and phosphorus; function to store and transmit genetic information * Deoxyribonucleic acid (DNA) contains the sugar deoxyribose * Ribonucleic acid (RNA) contains the sugar ribose * Proteins: macromolecules that contain carbon, hydrogen, oxygen, and nitrogen; needed by the body for growth and repair * Amino acids are compounds with an amino group on one end and a carboxyl group on the other end

A chemical reaction is a process that changes or transforms one set of chemicals into another set of chemicals * Reactants are the elements or compounds that go into a chemical reaction * Products are the elements or compounds that come out of a chemical reaction

Chemical reactions that give off energy often happen on their own, while chemical reactions that take in energy will not happen without a source of energy * Activation energy is the energy that is needed to get a reaction started

A catalyst is a substance that speeds up the rate of a chemical reaction by lowering a reaction’s energy rate * Enzymes are proteins that act as catalysts in living things * The reactants of enzyme-catalyzed reactions are known as substrates * The substrates bind to a site called the active site * Temperature, pH, and other molecules can affect how enzymes work