Chemical Changes—Forming New Kinds of Matter Chemical reactions Creating different chemical substances by forming and breaking chemical bonds. Remember: Atoms form chemical bonds to fill their outermost electron energy levels, achieving stability. There are several types of chemical bonds. We will discuss: Ionic bonds Covalent bonds

Ionic Bonds Atoms can gain or lose electrons to achieve a full outermost energy level. Atoms with charge are called ions. When an atom gives away an electron, it ends up with more protons than electrons and gains a positive charge; cation. When an atom accepts an electron, it ends up with more electrons than protons and gains a negative charge; anion. This process is called ionization. An ionic bond The attraction between oppositely charged ions Example: NaCl Sodium (Na) has one electron in its outer energy level. Chloride has seven electrons in its outer energy level. Sodium donates an electron to chloride, each achieving stability. The positively charged sodium is attracted to the negatively charged chloride.

Ion Formation

Covalent Bonds Atoms can achieve full outermost energy levels by sharing electrons instead of exchanging them. A covalent bond is formed by the sharing of electrons. The atoms sharing electrons sit close enough together so that their outer energy levels overlap. Single covalent bond- one pair of electrons is shared. H2 Double covalent bond- two pairs of electrons are shared. ethylene Triple covalent bond- three pairs of electrons are shared. N2

Covalent Bonds

Hydrogen Bonds The positive hydrogen end of one polar molecule is attracted to the negative end of another polar molecule. This attraction is a hydrogen bond. Hydrogen bonds hold molecules together. Since they do not hold atoms together, they are not considered true chemical bonds. Hydrogen bonds are very important in biology. They stabilize the structure of DNA and proteins. Water molecules can “stick” together with hydrogen bonds.

Water: The Essence of Life Water has special properties that make it an essential molecule for life. H2O Electrons are shared unequally by hydrogen and oxygen. This is a polar covalent bond. Oxygen has more protons than hydrogen. The electrons spend more time around oxygen than around hydrogen. The oxygen end of water is more negative. The hydrogen end of water is more positive.

Hydrogen Bonds

Mixtures and Solutions A mixture Matter that contains two or more substances that are not in set proportions A solution is a homogeneous mixture of ions or molecules of two or more substances. Components are distributed equally throughout. The process of making a solution is called dissolving. The solvent is the substance present in the largest amount. Frequently the solvent is a liquid. The solutes are the substances present in smaller amounts. Aqueous solutions are solids, liquids or gases dissolved in water.

Mixtures vs. Pure Substances

Water and Life The following properties of water make it essential for life: High surface tension Water molecules stick to each other via hydrogen bonds. Capillary action moves water through streams, soil, animals and plants. High heat of vaporization A lot of heat is required to break the hydrogen bonds holding water together. Large bodies of water absorb a lot of heat. Temperate climates Evaporative cooling

Water and Life Unusual density properties The universal solvent Ice is less dense than water, so ice floats. Allows aquatic life to survive in cold climates. The universal solvent Water can form hydrogen bonds with any polar or ionic compound. Therefore, many things can be dissolved in water.

Chemical Reactions A chemical change: When the bonds of compounds are made or broken, new materials with new properties are produced. Happens via chemical reactions. In a chemical reaction the elements remain the same, but the compounds they form and their properties are different.

Chemical Reactions and Energy Chemical reactions produce new compounds with less or more potential energy. Energy is released when compounds are made with less potential energy. Energy is used to make compounds with more potential energy.

Chemical Equations A chemical equation is a method of describing what happens in a chemical reaction. For example, photosynthesis is described by the following equation: Energy + 6CO2 + 6H2O → C6H12O6 + 6H2O Reactants-substances that are changed, usually on the left side of the equation. Products-new chemical substances formed, usually on the right side of the equation.

Five Important Chemical Reactions in Biology Oxidation–reduction Dehydration synthesis Hydrolysis Phosphorylation Acid–base reactions

Oxidation-Reduction Reactions Reactions in which electrons (and their energy) are transferred from one atom to another. Oxidation An atom loses an electron. Reduction An atom gains an electron. For oxidation to occur, reduction must also occur. Example: Respiration Sugar is oxidized to form carbon dioxide and oxygen is reduced to form water. Energy is released in the process. C6H12O6 + 6O2 → 6H2O + 6CO2+ Energy Sugar + oxygen → water+ carbon dioxide + energy

Dehydration Synthesis Reaction When two small molecules are joined to form a larger molecule, A molecule of water is released. Example: Joining amino acids to form proteins. NH2CH2CO-OH + H-NH CH2CO-OH  NH2CH2CO-NH CH2CO-OH + H-OH amino acid 1 + amino acid 2 = protein + water

Hydrolysis Reactions When a larger molecule is broken down into smaller parts, A water molecule is split Opposite of a dehydration synthesis Example: Digesting proteins into amino acids. NH2CH2CO-NH CH2CO-OH + H-OH  NH2CH2CO-OH + H-NH CH2CO-OH Protein + water = amino acid 1 + amino acid 2

Phosphorylation Reactions When phosphate groups are added to other molecules, Phosphate groups are clusters of oxygen and phosphate atoms. Bonds between phosphate groups and other molecules contain high potential energy. When these bonds are broken, the energy that is released can be used by the cell to do work. Phosphorylation reactions are commonly used to transfer potential energy. Q-P + Z  Q + Z-P

Acid-Base Reactions Occurs when ions from an acid interact with ions from a base. This type of reaction allows harmful acids and bases to neutralize one another. H+Cl- + Na+OH- → Na+Cl- + H+OH- Hydrocloric + Sodium Sodium + Water acid hydroxide chloride

Acids, Bases and Salts An acid A base Ionic compounds that release hydrogen ions (H+) into a solution Phosphoric acid, hydrochloric acid A base Compounds that release hydroxide ions (OH-) into a solution Sodium hydroxide, ammonia Because bases are negatively charged, they will react with a positively charged hydrogen in solution. The strength of an acid or base is determined by how completely it will dissociate in water. Strong acids release almost all of their hydrogen ions into water. Strong bases release almost all of their hydroxide ions into water.

Some Common Acids, Bases and Salts

Salts Neither acids nor bases Usually formed when acids and bases react The dissociated hydrogen ions and hydroxide ions join to form water. The remaining ions form ionic bonds, creating a salt. This is an example of neutralization: H+Cl- + Na+OH- → Na+Cl- + H+OH- Hydrocloric + Sodium Sodium + Water acid hydroxide chloride

pH A measure of hydrogen ion concentration Solutions with high hydrogen ion concentrations Have low pH Are acidic Solutions with low hydrogen ion concentrations Have a high pH Are basic There is a 10-fold difference in hydrogen ion concentration between solutions that differ by one pH unit. A solution with pH 4 has ten times as many hydrogen ions as a solution with pH 5.

The pH Scale