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.

It all begins with… Atoms – the smallest unit of matter 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

Atoms are composed of 3 main particles: (subatomic particles) Protons (+) Neutrons (0) Electrons (-)

Protons and Neutrons Nucleus – Center of atom that contains protons and neutrons. Both particles have about the same mass.

Electrons Electrons are about 1/1840 the mass of a proton. They are in constant motion in the space surrounding the nucleus. Electron cloud model

Atoms have equal numbers of electrons and protons. This makes an atom neutral

The Elements 116 known elements 92 occur naturally Only 25 are important to living organisms!

Elements Atomic number – number of protons Atomic mass – number of protons and neutrons. (amu) Atomic symbol – letters naming the element

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

More Electrons Electrons reside in something called shells. Shells are areas that surround the center of an atom. (aka. orbitals and energy levels)

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

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

Maximum Number of Electrons Max number of Valence Electrons Energy Level (Shell) Maximum Number of Electrons Max number of Valence Electrons 1 2 8 3 18 4 32 5 50 6 72 7 98

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.

Review How many protons, electrons, and neutrons are in… Boron Chlorine Sodium How many valence electrons does each of these elements have? What is the chemical formula for water?

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. (stealing) 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. https://www.youtube.com/watch?v=xweiQukBM_k

Ionic compounds form between metals and nonmetals

What If No One Will Give Up An Electron? Covalent Bonds - 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 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

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 = NM + M 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

Dot structures – Bonding

How many bonds are formed? Carbon Nitrogen Oxygen Hydrogen

Make Some Molecules Ammonia – NH3 Methane – CH4 Carbon Dioxide – CO2 Propane – C3H8 Urea – H4N2CO Glucose – C6H12O6

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!)

Our bodies use nutrients through chemical reactions! Reactants – molecules/elements prior to reaction Products – molecule/elements produced as a result of the reaction C6H12O6 + O2 CO2 + H2O Energy

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

Law of conservation of mass States that matter is not created or destroyed during a chemical reaction Even though the matter may change from one form to another, the same number of atoms exists before and after the change takes place! Mass of Reactants Mass of Products

Lets Make water! 2 H2 O2 2 H2O

Iron + Oxygen  Ironoxide

TAKE A LOOK AT THE NUMBERS Each made of TWO oxygen atoms Fe Fe O2 Fe2O3 Fe2O3 Fe Fe O2 O2 What about the PRODUCT? How many Oxygen molecules? How many Iron molecules? PRODUCT REACTANTS

How do we write it? Fe + O2  Fe2O3 N2 + H2  NH3 KClO3  KCl + O2

CO2 + H2O  C6H12O6 + O2 C8H18 + O2  CO2 + H2O NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2

Organic Compounds

Organic Compounds Make up living organisms Contain the element carbon 4 valence electrons = 4 covalent bonds

Organic Compounds The carbon atom is versatile, it can form large, complex compounds called macromolecules Monomer – Polymer –

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

Carbohydrates Made of C, H, & O H to O ratio is always 2:1 Monomer – monosaccharide Ex. Glucose, sucrose Polymer – polysaccharide Ex. Starch, cellulose, fiber Main energy source for living things

Carbohydrates Monosaccharide Examples: glucose – in many plant and animal tissues, most common monosaccharide fructose – in many fruits galactose – component of milk

Carbohydrates 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

Carb Sizes

Making bigger molecules Dehydration Synthesis – is a process that connects two large molecules By removing a water molecule

Breaking down big molecules Hydrolysis – is a process that separates two large molecules By adding a water molecule

Lipids Store a lot of energy Monomers – Glycerol & Fatty acids Polymers – Fats & Oils

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

Lipids 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)

Fats vs. Oils

Proteins Contain C, H, O, and N Monomers – amino acids 25 different kinds (R groups) Polymers – proteins

Proteins Shape of protein is important to its function! Chains of AA’s are folded and twisted giving each protein a unique shape Ionic charges and hydrogen bonds help maintain protein’s shape Shape of protein is important to its function! https://www.youtube.com/watch?v=TfYf_rPWUdY

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

Dehydration synthesis!

Nucleic Acids Contain C, H, O, N plus phosphorus (P) Monomer – Nucleotide 5 of them (A, T, C, G, U) Made of sugar, phosphate, and base Polymer – Nucleic Acid Ex. DNA, RNA

Nucleotide Nucleic Acids

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