Chapter Checkpoints
These are some important ideas you are learning in Chapter 2:

Atoms, Bonds, and Molecules: Fundamental Building Blocks
Protons (p+) and neutrons (n_) comprise the nucleus of an atom. Electrons (e^?) orbit the nucleus.

All elements are composed of atoms but differ in the numbers of protons, neutrons, and electrons they possess.

Elements are identified by ATOMIC WEIGHT or MASS or by ATOMIC NUMBER

Isotopes are varieties of one element which contain the same number of protons but different numbers of neutrons.

The number of electrons in an element's outermost orbital determines its chemical nature. As the outer orbital fills with electrons, its reactivity decreases.

Bonds and Molecules
Covalent bonds are chemical bonds in which electrons are SHARED between atoms. Equally distributed electrons form NONPOLAR covalent bonds, whereas unequally distributed electrons form POLAR covalent bonds.

Ionic bonds are chemical bonds in which the outer electron orbital either DONATES or RECEIVES electrons from another atom so that the outer orbital of each atom is completely filled.

Hydrogen bonds are weak chemical bonds that form between covalently bonded hydrogens and either oxygens or nitrogens on DIFFERENT molecules.

Chemical energy is generated by the movement of electrons from one atom or molecule to another. Chemical equations express movement of energy in chemical reactions such as synthesis or decomposition reactions.

Solutions are mixtures of solutes and solvents which cannot be separated by filtration or settling.

The pH, ranging from a highly ACIDIC solution to a highly BASIC solution, refers to the concentration of hydrogen ions. It is expressed as a number from 0?14.

Biologists define organic molecules as those containing carbon and hydrogen together.

Carbon is the backbone of biological compounds because of its ability to form single, double, or triple covalent bonds with many different elements.

Functional groups are specific arrangements or organic molecules that confer distinct properties to organic compounds, including chemical reactivity.

Macromolecules: Molecular Superstructures
Macromolecules are very large organic molecules (polymers) built up by polymerization of smaller molecular subunits (monomers).

Carbohydrates are biological molecules whose polymers are chains or rings of monomers linked together by glycosidic bonds. Their main functions are protection and support (in organisms with cell walls) and also nutrient and energy stores.

Lipids are biological molecules whose polymers are chains or rings of monomers linked together by ester bonds or ?CH? linkages. Their main functions are cell components, cell secretions, and nutrient and energy stores.

Proteins are biological molecules whose polymers are chains of amino acid monomers linked together by peptide bonds.

Proteins are called the ``shapers of life'' because of the many biological roles they play in cell structure and cell metabolism.

Protein shape determines protein function. Shape is dictated by amino acid composition, and by the ph and temperature of the protein's immediate environment.

Nucleic acids are biological molecules whose polymers are chains of nucleotide monomers linked together by phosphate-pentose sugar covalent bonds. Double-stranded nucleic acids are linked together by hydrogen bonds. Nucleic acids are information molecules which direct cell metabolism and reproduction. Nucleotides such as ATP also serve as energy transfer molecules in cells.

Cells: Where Chemicals Come to Life
As the atom is the fundamental unit of matter, so is the cell the fundamental unit of life.

All true cells contain biological molecules which carry out processes that define life: metabolism and reproduction. The functions of motility, protection, storage, and transport support these two basic processes.

The cell membrane is of critical importance to all cells because it controls the interchanges between the cell and its environment.

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