The Chemistry of Life Chapter 2

Why should we study chemistry in Biology? Life depends on chemistry!

Life depends on chemistry! When you eat food or inhale oxygen, your body uses these materials in chemical reactions that keep you alive. Just as buildings are made from bricks, steel, glass, and wood, living things are made from chemical compounds. Wouldn’t you want an architect to understand building materials? Same idea applies to geneticists, ecologists, zoologists, botanists, biologists, and etc.

Atoms The study of chemistry begins with the basic unit of matter…the History Greeks were first to try to explain chemical reactions 400 BC: thought all matter composed of: Fire Earth Water Air Democritus first used word “atomos”, meaning indivisible Atom

Atoms Atoms are composed of 3 main particles: (subatomic particles) Protons (+) Neutrons Electrons (-)

Protons and Neutrons Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom. Both particles have about the same mass.

Electrons Electrons are negatively charged with about 1/1840 the mass of a proton. They are in constant motion in the space surrounding the nucleus.

Atoms Atoms have equal numbers of electrons and protons. Because these subatomic particles have equal but opposite charges, atoms are neutral.

Elements Elements are the building blocks of all matter. Elements cannot be decomposed into simpler matter. Group Number: 1 2 3 4 5 6 7 8

The Elements 110 known elements 88 occur naturally The 110 elements form a plethora of compounds, just as 26 letters of the alphabet make a seemingly endless number of words.

Atomic Number Counts the number of protons in an atom

Atomic Number on the Periodic Table 11 Na Atomic Number Symbol

All atoms of an element have the same number of protons 11 Na 11 protons Sodium

Atomic Mass Mass of an atom. Approximately equal to the number of protons and neutrons Find number of neutrons by subtracting the number of protons from the mass.

Review: An element's atomic number tells how many protons are in its atoms. An element's mass number tells how many protons and neutrons are in its atoms.

Learning Check 1 State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons 2) 7 protons 2) 16 protons 3) 56 protons

The Periodic Table

Isotopes What does that mean? Isotopes are atoms that have the same atomic number but different mass number. Most elements have two or more isotopes. Same chemical properties because the electron number does not change. What does that mean?

Isotope symbols X A Z Mass number Atomic number

B Example How many protons does this have? 11 5 How many protons does this have? How many neutrons does this have? Is the “5” necessary ?

More about isotopes: Some isotopes have unstable nuclei which break down over time. They are called radioactive isotopes Some radiation is harmful.

Radiation can also be useful Radioactive Dating Tracers with X-rays Cancer Treatment Kill bacteria

More About Atomic Structure The center of the atom is called the nucleus. Electrons live in something called shells. Shells are areas that surround the center of an atom. A shell is sometimes called an orbital or energy level.

More About Electrons Every shell can hold only so many electrons The further from the nucleus, the more electrons a shell can hold

Valence Electrons The electrons on the outside edge of the atom This is where the action is- where bonding takes place Atoms have no more than 8 valence electrons

The Octet Rule: Atoms will combine to form compounds in order to reach eight electrons in their outer energy level. This is very stable! Atoms with less than 4 electrons tend to lose electrons. Atoms with more than 4 electrons tend to gain electrons.

Compound Two or more elements chemically combined in specific proportions Examples: Water H2O Salt NaCl Sugar C6H12O6 Chemical Formulas are used to represent compounds Two types of compounds: Ionic Covalent

Ionic Compounds Form when electrons are transferred from one atom to another. Ions - Atoms with a net charge due to gaining or losing electrons Gaining electrons gives an ion a negative charge Losing electrons gives an ion a positive charge **If they have to choose, atoms would rather be stable (with a full “octet”) than neutral.

How Does This Happen? Some atoms have a few too many electrons Some atoms only need a few electrons

What do you do if you are a sodium (Na) atom with one extra electron? Go look for an atom that wants it!

Ionic Bonding Negative ions and positive ions are held together by ionic bond.

Ionic compounds form between metals and nonmetals

What If No One Will Give Up An Electron? Atoms with less than 8 valence electrons can move close to each other and share their electrons The electrons spend their time around both atoms. And they lived happily ever after!

Covalent Bonds Formed when a pair of electrons is shared between two atoms. Sometimes the atoms share two pairs of electrons and form a double bond, or three pairs of electrons to form a triple bond. Structures formed by covalent bonds are molecules.

Covalent compounds form between 2 nonmetals

Van der Waals Forces There are small attractive forces between all atoms Help to hold molecules to each other Ex: Gecko

Let’s summarize what we know! Why do compounds form? Atoms are trying to get 8 valence electrons How do compounds form? By ionic (e- transfer) or covalent (e- sharing) bonding How can you tell if a compound is ionic or covalent? By the types of elements in the compound (ionic = M + NM covalent = NM + NM)

Learning Check 2: Indicate whether a bond between the following would be 1) Ionic 2) covalent ___ A. sodium and oxygen ___ B. nitrogen and oxygen ___ C. phosphorus and chlorine ___ D. calcium and sulfur ___ E. chlorine and bromine

2-2 Water is a Polar Molecule Polar: Molecule in which electrons are shared unevenly between atoms, causing each end of the molecule to have a slight charge Negative end Positive end

This causes water to be attracted to other polar or charged particles Water is attracted to ions Water is attracted to itself, forming hydrogen bonds

Hydrogen Bonds In Water Are Responsible For: Adhesion Attraction between molecules of different substances Graduated cylinder Cohesion Attraction between molecules of the same substance Drops of water on a penny Ex: Surface Tension Jesus Lizard

Types of Chemical Substances Compounds and Elements are called pure substances. Most matter is neither of these.

Mixtures Mixtures are combinations of substances held together by physical forces, not chemical bonds. Each substance keeps its own properties

Mixtures may be either: Solutions Colloids Suspensions

Solutions Have small particles Are transparent (not the same as colorless) Do not separate Water solutions are very common in biological systems Examples: salt water, kool-aid, air, brass, vinegar

Colloids Have medium size particles Do not separate Examples: fog, whipped cream, milk, cheese, mayonnaise

Suspensions Have very large particles Settle out (separates into layers) Examples: blood platelets, muddy water, calamine lotion, oil & water, Italian salad dressing

pH Scale Measures concentration of hydrogen ions in a solution Ranges from 0 to 14 7 is neutral 0-7 have more hydrogen ions (H+) and are acidic 7-14 have more hydroxide ions (OH-) and are basic

Acids, Bases, and pH Water molecules form ions H2O H+ + OH- Water hydrogen ion + hydroxide ion Very few ions are formed in pure water, but there are equal numbers of hydrogen and hydroxide ions Water is neutral!

pH of common substances

pH and Homeostasis Maintaining a pH between 6.5 and 7.5 is important in cells Dissolved compounds called buffers control pH Proteins Phosphates Hydrogen carbonate

Chemical Reactions When one set of chemicals changes into another set of chemicals, a chemical reaction occurs Bonds are either broken or formed (or both!)

Chemical Equations 2H2O Represent a reaction Give the types and amounts of substances that react and form Reactants Products 2H2 + O2 “yields” “yields” 2H2O

Evidence of a Chemical Reaction Formation of a precipitate (a solid substance separated from a liquid) Gas is evolved (seen by bubbles forming in a liquid) Change in heat or light energy

Organic Compounds

Organic Compounds Make up most of living organisms Contain bonds between two or more carbon atoms C can easily bond with up to 4 other elements 4 valence electrons = 4 covalent bonds

Organic Compounds Carbon atom is versatile, can be “backbone” of long chains or rings Organic molecules can be extremely large and complex; these are called macromolecules

Organic Compounds Four main types of organic macromolecules: Carbohydrates Lipids Proteins Nucleic Acids

Carbohydrates Made of C, H, & O Main energy source for living things Breakdown of sugars supplies immediate energy for cell activities Extra sugar is stored as complex carbs called starches

Carbohydrates Single sugar molecules are called monosaccharides Examples: glucose – in many plant and animal tissues, most common monosaccharide fructose – in many fruits galactose – component of milk

Carbohydrates Large molecules of many monosaccharide are polysaccharides Examples: glycogen – animals use to store excess sugar plant starch – plants use to store excess sugar cellulose – fibers that give plants their rigidity & strength

Lipids Store more energy than CHOs because the chains are longer Ex: Fats, oils, waxes Won’t dissolve in water

Lipids Important parts of biological membranes and waterproof coverings Steroids are lipids that act as chemical messengers

Lipids Many lipids are made from a glycerol combined with fatty acids If all carbons have single bonds, lipid is saturated Ex: butter, lard, animal fat (usually solid at room temperature) If any carbons have double or triple bonds, lipid is unsaturated Ex: vegetable oil, fish oil, peanut oil (usually liquid at room temperature)

Proteins Contain C, H, O, plus nitrogen Formed from amino acids joined together More than 20 amino acids can be joined in any order or number to make countless proteins (think of how many words can be made from 26 letters!)

Proteins Chains are folded and twisted giving each protein a unique shape Van der Waals forces and hydrogen bonds help maintain protein’s shape Shape of protein is important to its function!

Proteins Provide structure Aid chemical activities in your body Ex: Collagen- makes up your skin, muscles & bones Aid chemical activities in your body Ex: Enzymes- work to speed up rxns in your body Transport substances into or out of cells Help fight diseases

Nucleic Acids Contain C, H, O, N plus phosphorus Formed by bonding of individual units called nucleotides Nucleic Acid nucleotide

Nucleic Acids Store and transmit hereditary information Ex: DNA (deoxyribonucleic acid) RNA (ribonucleic acid)