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The Chemistry of Life Chapter 2 Why should we study chemistry in 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 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 Energy Level (Shell) Maximum Number of Electrons Max number of Valence Electrons 1 2 2 2 8 8 3 18 8 4 32 8 5 50 8 6 72 8 7 98 8 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 1. How many protons, electrons, and neutrons are in… – Boron – Chlorine – Sodium 2. How many valence electrons does each of these elements have? 3. What is the chemical formula for water? Compound • Two or more elements chemically combined in specific proportions • Examples: – Water – Salt – Sugar H 2O NaCl 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 Energy C6H12O6 + O2 CO2 + H2O Chemical Equations • Represent a reaction • Give the types and amounts of substances that react and form Reactants 2H2 + O2 “yields” “yields” Products 2H2O 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 Fe Fe Fe Fe How many Iron molecules? O2 Fe2O3 O2 Fe2O3 O2 How many Oxygen molecules? What about the PRODUCT? How do we write it? Fe + O2 N 2 + H2 KClO3 Fe2O3 NH3 KCl + O2 CO2 + H2O C8H18 + O2 C6H12O6 + CO2 + O2 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 liquid at room temperature) (usually Fats vs. Oils Proteins • Contain C, H, O, and N • Monomers – amino acids – 25 different kinds (R groups) • Polymers – proteins Proteins • 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 – 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)