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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. • Wouldn’t you want an architect to understand building materials? Same idea applies to geneticists, ecologists, zoologists, botanists, biologists, and etc. • 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 • 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. Electron • 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 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 simple matter. Group Number: 6 7 8 1 2 3 4 5 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 Atomic Number Symbol 11 Na All atoms of an element have the same number of protons 11 protons Sodium 11 Na 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 or 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 Solution AT 1 State the number of protons for atoms of each of the following: A. Nitrogen 2) 7 protons B. Sulfur 2) 16 protons C. Barium 3) 56 protons The Periodic Table Isotopes • 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. Isotope symbols Mass number A Z Atomic number X Example 11 B 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 Cancer Treatment Tracers with X-rays Kill bacteria Compounds • Two or more elements chemically combined in specific proportions • Examples: – Water – Salt – Sugar H2O NaCl C6H12O6 Chemical Formulas are used to represent compounds 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. Ions • Atoms with extra electrons or missing electrons – Extra electrons give an ion a negative charge – Missing electrons give an ion a positive charge If they have to choose, atoms would rather be stable 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? Go look for an atom that wants it! Ionic Bonding • Attraction that holds oppositely charged ions together. • Formed by the transferring of electrons 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! Van der Waals Forces • There are small attractive forces between all atoms • Help to hold molecules to each other • Ex: Gecko Why do compounds form? • Atoms are trying to get 8 valence electrons How do compounds form? • By ionic or covalent bonding How can you tell if a compound is ionic or covalent? • By the types of elements in the compound • Ionic compounds form between metals and nonmetals • Covalent compounds form between 2 nonmetals Note Question : 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 Indicate whether a bond between the following would be 1) Ionic 2) covalent _1_ A. sodium and oxygen _2_ B. nitrogen and oxygen _2_ C. phosphorus and chlorine _1_ D. calcium and sulfur _2_ E. chlorine and bromine 2-2 Water is a Polar Molecule • Electrons are shared unevenly between the oxygen atom and the hydrogen atoms 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: • Surface Tension – Jesus Lizard • Adhesion – Attraction between molecules of different substances – Graduate cylinder • Cohesion – Attraction between molecules of the same substance – Drops of water on a penny Acids, Bases, and pH • Water molecules form ions – H2O – Water H+ hydrogen ion OH+ hydroxide ion + • Very few ions are formed in pure water, but there are equal numbers of hydrogen and hydroxide ions • Water is neutral! 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 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 2 or more substances change into other substances, a chemical reaction occurs • Bonds are either broken or formed Chemical Equations • Represent a reaction • Give the types and amounts of substances that react and form • Reactants “yields” Products • 2H2 + O2 “yields” 2H2O Evidence of a Chemical Reaction • Precipitate is formed • Gas is evolved • Change in heat or light energy Organic Compounds Organic Compounds • Make up most of living organism • C atom is “backbone” • C can easily bond with 4 other elements Carbohydrates • Energy source • Made of C, H, & O – Ex: Glucose (a sugar) – Polysaccharides: many simple sugars linked together like a chain Lipids • Store more energy than CHOs because the chains are longer • Ex: Fats, oils, waxes • Won’t dissolve in water 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 Nucleic Acids • Store hereditary information –Ex: DNA(deoxyribonucleic acid) RNA(ribonucleic acid)