Chapter 2 The Chemistry of Life

All Matter Consists of Elements Made of Atoms Atoms contain: Protons: positive charge; have mass Neutrons: no charge; have mass Electrons: negative charge; negligible mass

FIGURE 2.1 An atom of helium, showing protons and neutrons in the nucleus and electrons occupying a region around the nucleus.

TABLE 2.1 REVIEW OF SUBATOMIC PARTICLES

Chemical bonds form between the atoms of a compound The atoms in a compound are held together by covalent, ionic or hydrogen bonds

FIGURE 2.7 Atoms of hydrogen, carbon, and oxygen. Each of the concentric circles around the nucleus represents a shell occupied by electrons.

Covalent Bonds Covalent bonds are the strongest bonds Form when two or more atoms share the electrons in their outer shells

Single Covalent Bonds FIGURE 2.8a Covalent bonds form when electrons are shared between atoms. Shown here are examples of single, double, and triple covalent bonds. For each example, the structural formula is shown on the far right.

Double Covalent Bonds FIGURE 2.8b Covalent bonds form when electrons are shared between atoms. Shown here are examples of single, double, and triple covalent bonds. For each example, the structural formula is shown on the far right.

Triple Covalent Bonds FIGURE 2.8c Covalent bonds form when electrons are shared between atoms. Shown here are examples of single, double, and triple covalent bonds. For each example, the structural formula is shown on the far right.

Ionic Bonds An ion is an atom or group of atoms with a positive or negative electrical charge Ionic bonds, weaker than covalent bonds, result from the attraction of oppositely charged ions, rather than shared electrons

FIGURE 2.9 An ionic bond involves the transfer of electrons between atoms. Such a transfer creates oppositely charged ions that are attracted to one another.

Hydrogen Bonds Hydrogen bonds are the attraction formed between a slightly positively charged hydrogen atom and another slightly negatively charged atom Many hydrogen bonds can collectively add up to formation of tightly bound molecules, e.g., DNA double helix

Hydrogen Bonds Hydrogen bonds account for the unique properties of water and the geometric shape of many biological molecules

FIGURE 2.10a The hydrogen bonds of water

FIGURE 2.10b The hydrogen bonds of water

TABLE 2.2 REVIEW OF CHEMICAL BONDS

Acids and Bases Acids and bases react differently to water Acids release hydrogen ions (H+) when placed in water and bases produce hydroxide ions (OH-) when added to water

The pH Scale: Each unit equals A 10 fold change In H+ concentration FIGURE 2.12 The pH scale and the pH of some body fluids and other familiar substances.

Acids and Bases The lower the pH on the pH scale, the greater the acidity and the higher the pH, the more basic a solution

TABLE 2.3 REVIEW OF THE CHARACTERISTICS OF ACIDS AND BASES

Synthesis and Hydrolysis of Polymers Biological macromolecules are the giant molecules of life (proteins, nucleic acids, lipids, carbohydrates) They are long chains called polymers made of repeating units called monomers

Synthesis of Polymers When polymers are made, water is removed and the reaction is called a dehydration synthesis

FIGURE 2.13a Formation and breaking apart of polymers.

Hydrolysis of Polymers Conversely, when the same molecules are broken apart, water is added and the reaction is a hydrolysis

FIGURE 2.13b Formation and breaking apart of polymers.