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THE CHEMICAL BASIS OF LIFE CHAPTER 4 4.1 Life Requires… • What are humans and other organisms made of? • • • • • Matter What is matter? Anything that occupies space and has mass. What are examples of matter? Rock, wood, air, metal, animals. WHAT ARE THESE? • What is matter made of? • Elements • Element: • A pure substance that can not be broken down into other substances by chemical means. • Are often described as the “basic ingredients” of matter. WHICH ELEMENTS ARE ESSENTIAL FOR LIFE? • Oxygen • Carbon • Hydrogen • Nitrogen • Make up 96% of the living matter in our body. THE OTHER 4 % ARE • Calcium, Phosphorus, Potassium, Sulfur, and few other elements. • These elements are called trace elements. • Trace elements: • Elements that make up less than .01% of your body mass, but are still critical to have. • Iron is a trace element (.004%) • We need iron in our system to regulate our oxygen in our blood. • We get these elements in our diet. WHAT DO YOU GET WHEN YOU MIX SODIUM(NA) AND CHLORINE (CL)? • Sodium chloride (NaCl)= salt! • This is an example of a compound. • Compound: • Is a substance containing two or more elements that are chemically combined in a fixed ratio. 4.2 CHEMICAL PROPERTIES • The smallest possible particle is called an atom. • Atom= atomos= invisible. ATOM • Atoms are made up of even smaller particles called subatomic particles. • What are the three subatomic particles? • Protons • Neutrons • Electrons WHAT KIND OF CHARGE DO THESE HAVE? • Protons: • Positive electrical charge + • Neutrons: • No electrical charge 0 • Electrons: • Negative electrical charge - WHERE CAN THE PROTONS AND NEUTRONS BE FOUND IN AN ATOM? • Nucleus. • Electrons (less mass than neutrons are found outside the nucleus) • All atoms of an element have the same number of protons. This is called the atomic number. • How many protons are in Carbon? •6 • Atomic number= number of protons! • Number of protons= Atomic number • Number of electrons= Number of protons= Atomic number • Number of neutrons= Mass number – Atomic number HOW MANY ELECTRONS IS KRYPTON? Mass number = (Number of protons) + (Number of neutrons) 84 = (Number of protons) + (Number of neutrons) 84 = 36 (number of neutrons) 48 number of neutrons • Some elements have alternate forms called isotopes. • Isotopes: • An element that has the same number of protons but different number of neutrons. • Carbon 12 makes up of 99% of carbon. • Carbon 13 and Carbon 14 are extremely rare. • Carbon 14 is unstable and radioactive. • Carbon 14 is a radioactive isotope. • Radioactive isotope: • The nucleus decays and gives off radiation. How does an atom’s structure determine how it reacts with other atoms? • Electrons differ in the amount of energy they have and how tightly they are held by the protons in the nucleus. • An atom’s electrons belong to certain energy levels. • Usually it is the electrons in the highest energy level that determines how atoms react. • The first or lowest energy level (closest to the nucleus) can hold 2 electrons. • The second energy level can hold 8 electrons. • Helium has 2 electrons. Both of those electrons are found in the lowest energy level. • Since the lowest energy level is fully occupied it is less likely to react. WHAT WILL CARBONS ELECTRONS LOOK LIKE? • Carbon has 6 electrons. • Since 8 electrons can fit on the secondary energy level and is not complete (stable) the outside 4 electrons are more likely to react. 4.3 CHEMICAL BONDS • What happens to the electrons when you mix sodium NA and chlorine CL? • The sodium that has one electron in its outer level will move to the chlorine that has 7 electrons on the outer level to make it stable. • Now both are stable on the outside level. • This is called an ionic bond. • Ionic bond: • Occurs when an atom transfers an electron to another atom. • Now that chlorine gained an electron is has a – 1 charge. • Sodium lost an electron so now its charge is +1. • The two atoms are now referred to as ions. • Ions: • Atoms that have become electrically charged as a result of gaining or losing electrons. • Covalent bond: • Forms when two atoms share electrons. • Number of bonds: The number of bonds an atom can form is equaled to the number of additional electrons that will fill its highest energy level. • How many bonds can hydrogen have? • 1 • How many bonds can oxygen have? • 2 • Two or more atoms held together by covalent bonds form a molecule. • Chemical formula: number and types of atoms in a molecule • Structural formula: how atoms in a molecule are linked by bonds. • The formation of one or more new substances is called a chemical reaction. • Reactants: the starting materials for the reaction • Products: the ending materials for the reaction 4.4 UNIQUE PROPERTIES OF WATER • Water is a polar molecule. A polar molecule is when the opposite ends have opposite electric charges. • The hydrogen in the water molecule is slightly positive. The oxygen in water is slightly negative. • Since opposites attract… two water molecules are attracted to each other. • Have you ever fell asleep before it rains and wake up to go to the bus and see water covering everything? PROPERTIES OF WATER • Adhesion: Water attracted to other substances. • Cohesion: Water attracted to water. • Objects can float because of waters surface tension • Surface tension: The bond between water molecules. • Does ice sink or float? • Water is unique because its solid form is less dense that its liquid form. WATER CAN DISSOLVE OTHER SUBSTANCES • What happens when you mix salt in water? • It dissolves. • You just made a solution. • Solution: • A mixture of two or more substances. • Solvent: the substance that dissolved the other substance and is present in the greater amount. • Solute: the substance that is dissolved and is present in a lesser amount. • If you take a pack of salt and mix in water… which is the solute and solvent? • Solute • Salt • Solvent Water ACIDS AND BASES • Hydrogen ions (positive charge) makes things more acidic. • Acid: • H+ ions added. • Base: • The removal of H+ ions. PH SCALE • pH scale: • Describes how acidic or basic a solution is. • Ranges from 0 (extremely acidic) to 14 (extremely basic) • 7 is neutral (pure water) • Most living cells are near 7. • Buffers: • Substances that cause a solution to resist changes in pH. • Human blood normally has a pH of 7.4 • When bloods pH decrease (drink lemon juice) and becomes more acidic buffers come in and resist the blood to drop any lower and acidic.