Essential Chemistry for Biology Chapter 2

Why Chemistry?? Chemicals make up everything! Body Environment Food

Basic Chemistry Matter Elements Anything that takes up space and has mass Can exist as a liquid, solid, or gas Made up of atoms Elements Basic building block of matter 92 naturally occurring elements

Basic Chemistry Only 6 elements that make up most of the body weight of organisms C Carbon H Hydrogen N Nitrogen O Oxygen P Phosphorus S Sulfur

Trace Elements Trace elements make up 0.01% of human body weight, but still very important

Each Element Consists of ONE Kind of Atom Smallest unit that retains the properties of a given element And to enter a chemical reaction Composed of subatomic particles: Protons (p+) Neutrons Electrons (e-) Move @ atomic nucleus Usually (e-) = (p+) Electrically neutral

Atomic Symbol Atomic Mass = Number of Protons + Number of Neutrons Atomic Number = The Number of Protons in the Nucleus

Why are electrons so important?? determine the chemical behavior of atoms Part of atom that comes close enough for interactions associated with energy the field of energy around an atom is arranged as levels called electron shells

Electron Shells have specific numbers of orbitals that may be filled with electrons atoms that have incomplete electron orbitals tend to be more reactive atoms will lose, gain, or share electrons in order to fill completely their outermost electron shell these actions are the basis of chemical bonding

Valence Shell

Molecules and Compounds Chemical bonding that joins atoms Some contain atoms of only one element N2 Compounds Atoms of two or more different elements H2O Mixture Two or more molecules mingling together

Chemical Bonds Atoms are held together by bonds 3 main types: Ionic bond Accept or donate electrons Covalent bond Share one or more electrons Hydrogen bond

Ionic Bond Atoms gain and lose electrons Ion Ionic bond Balance between protons and electrons shifts Become “ionized” Ion Atom that has a charge Losing an electron results in a net positive Gaining an electron results in a net negative charge Ionic bond Association of two ions that have opposing charges

Which will form an ionic bond? Chlorine (Cl) Argon (Ar) Potassium (K) Helium (He)

Can Mg and Cl form an ionic bond? Magnesium (Mg) Chlorine (Cl)

Covalent Bond Covalent bond Bond Notation Stable and stronger than ionic bonds Atoms share electrons Each atom will have a completed outer shell Bond Notation Single covalent bonds are written as H-H Double covalent bonds are written as O=O

A covalent bond can be nonpolar or polar Nonpolar covalent bond Sharing of electrons between atoms is fairly equal Polar covalent bond Unequal sharing of electrons

Hydrogen Bond Hydrogen bond Weak attraction Form and break easily Occurs between polar molecules Polar bonds have charges on either end and often attract to each other

Water molecules contain two covalent bonds

Chemical Reactions Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones Reactants Starting materials Products End materials Chemical reactions cannot create or destroy matter, They only rearrange it

Hydrogen Bonds Give Water Unique Properties Heat Storage water temperature changes slowly and holds temperature well Ice Formation few hydrogen bonds break at low temperatures water becomes less dense as it freezes because hydrogen bonds stabilize and hold water molecules farther apart High Heat of Vaporization at high temperatures, hydrogen bonds can be broken water requires tremendous energy to vaporize because of all the hydrogen bonds that must be broken

Hydrogen Bonds Give Water Unique Properties Water molecules are sticky cohesion – when one water molecule is attracted to another water molecule adhesion – when polar molecules other than water stick to a water molecule

Hydrogen Bonds Give Water Unique Properties Water dissolves other polar substances Solvent Ions and polar molecules easily dissolve in it Solute A dissolved substance Hydrophilic water-loving molecules form hydrogen bonds with water Hydrophobic water-fearing molecules do not form hydrogen bonds with water

Acids and Bases When water ionizes, it releases an equal number of hydrogen ions (H+) and hydroxide ions (OH-) Some substances release more or fewer or each Acids - Excess hydrogen ions Bases - Excess hydroxide ions

Acidic and Basic Solutions Acidic Solutions Sharp, sour taste Molecules that dissociate in water Release hydrogen ions (H+) Basic Solutions Bitter taste Molecules that either take up hydrogen ions (H+) or release hydroxide ions (OH-)

pH Scale The pH Scale Buffer Ranges from 0 - 14 pH below 7 is acidic [H+] > [OH-] pH above 7 is alkaline [OH-] > [H+] pH of 7 is neutral [H+] = [OH-] Buffer Chemical or combination of chemicals that keeps pH within normal limits

pH = -log[H+] Water Ionizes The amount of ionized hydrogen from water in a solution can be measured as pH The pH scale is logarithmic, which means that a pH scale difference of 1 unit actually represents a 10-fold change in hydrogen ion concentration pH = -log[H+]

The pH scale