1 1 Chapter 2 Essential Chemistry for Biology Biology and Society: More Precious than Gold A drought is a period of abnormally dry weather that changes the environment and one of the most devastating disasters. 2 Biology and Society: More Precious than Gold 3 Biology and Society: More Precious than Gold 4 Droughts can cause severe crop damage, shortages of drinking water, dust storms, Throughout human history, droughts have helped wipe out societies and even whole civilizations. Droughts are catastrophic because life cannot exist without water. famine, habitat loss, and mass migration.
2 SOME BASIC CHEMISTRY 5 Matter: Elements and Compounds 6 Take any biological system apart, and you eventually end up at the chemical level. Matter is anything that occupies space and has mass. Chemical reactions are always occurring in the human body. Matter is found on Earth in three physical states: solid, liquid, and gas. Matter: Elements and Compounds Matter is composed of chemical elements. An element is a substance that cannot be broken down into other substances by chemical reactions. 7 Figure 2.1a H Atomic number (number of protons) Element symbol Mass number (number of protons plus neutrons) 6 C 12 He 8 There are 92 naturally occurring elements on Earth. All of the elements are listed in the periodic table. Li Be Na Mg K Ca Sc Rb Sr Y Ti Zr V Cr Mn Fe Co Ni Nb Mo Tc Ru Rh Pd B Al Cu Zn Ga Ag Cd In C N Si P Ge As Sn Sb O S F Cl Se Br Te I Ne Ar Kr Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg TI Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
3 Matter: Elements and Compounds 9 Figure Carbon (C): 18.5% Twenty-five elements are essential to people. Four elements make up about 96% of the weight of most cells: oxygen, carbon, hydrogen, and nitrogen. Hydrogen (H): 9.5% Nitrogen (N): 3.3% Oxygen (O): 65.0% Calcium (Ca): 1.5% Phosphorus (P): 1.0% Potassium (K): 0.4% Sulfur (S): 0.3% Sodium (Na): 0.2% Chlorine (Cl): 0.2% Magnesium (Mg): 0.1% Trace elements: less than 0.01% Boron (B) Chromium (Cr) Cobalt (Co) Copper (Cu) Fluorine (F) Iodine (I) Iron (Fe) Manganese (Mn) Molybdenum (Mo) Selenium (Se) Silicon (Si) Tin (Sn) Vanadium (V) Zinc (Zn) Matter: Elements and Compounds 11 Figure 2.3a 12 Trace elements are required in only very small amounts and essential for life. An iodine deficiency causes goiter. Fluorine is added to dental products and drinking water and helps to maintain healthy bones and teeth.
4 Matter: Elements and Compounds 13 Atoms 14 Elements can combine to form compounds. Each element consists of one kind of atom. Compounds are substances that contain two or more elements in a fixed ratio. An atom is the smallest unit of matter that still retains the properties of an element. Common compounds include NaCl (table salt) and H 2 O (water). The Structure of Atoms 15 Figure Atoms are composed of subatomic particles. A proton is positively charged. An electron is negatively charged. A neutron is electrically neutral. Nucleus 2e Protons Neutrons Electrons Nucleus Most atoms have protons and neutrons packed tightly into the nucleus. Electron cloud The nucleus is the atom s central core. Electrons orbit the nucleus.
5 The Structure of Atoms 17 Isotopes 18 Elements differ in the number of subatomic particles in their atoms. The number of protons, the atomic number, determines which element it is. Mass is a measure of the amount of material in an object. Isotopes are alternate mass forms of an element. Isotopes have the same number of protons and electrons but differ in their number of neutrons. An atom s mass number is the sum of the number of protons and neutrons in its nucleus. Table Isotopes 20 The nucleus of a radioactive isotope decays spontaneously, giving off particles and energy. Radioactive isotopes have many uses in research and medicine. They can be used to determine the fate of atoms in living organisms. They are used in PET scans to diagnose heart disorders and some cancers.
6 Electron Arrangement and the Chemical Properties of Atoms 22 Figure Of the three subatomic particles, only electrons are directly involved in the chemical activity of an atom. Electron First electron shell (can hold 2 electrons) Outer electron shell (can hold 8 electrons) Electrons orbit the nucleus of an atom in specific electron shells. The farther an electron is from the nucleus, the greater its energy. The number of electrons in the outermost shell determines the chemical properties of an atom. Hydrogen (H) Atomic number = 1 Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Chemical Bonding and Molecules 24 Ionic Bonds 25 Chemical reactions enable atoms to give up or acquire electrons, completing their outer shells. Chemical reactions usually result in atoms staying close together and being held together by attractions called chemical bonds. When an atom loses or gains electrons, it becomes electrically charged. Charged atoms are called ions. Ionic bonds are formed between oppositely charged ions.
7 26 Figure Complete outer shells Na Cl Na + Cl Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl Chloride ion Sodium chloride (NaCl) Animation: Ionic Bonds Right-click slide / select play Covalent Bonds 28 Figure 2.8 Electron configuration Structural formula Space-filling model 30 Ball-and-stick model A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. Covalent bonds are the strongest of the various bonds. Covalent bonds hold atoms together in a molecule. The number of covalent bonds an atom can form is equal to the number of additional electrons needed to fill its outer shell. H H Hydrogen gas (H 2 ) O O Oxygen gas (O 2 ) H H C H H Methane (CH 4 )
8 Hydrogen Bonds Water is a compound in which the electrons in its covalent bonds are not shared equally. This causes water to be a polar molecule, one with an uneven distribution of charge. Animation: Water Structure Right-click slide / select play Hydrogen Bonds 33 Figure The polarity of water results in weak electrical attractions between neighboring water molecules. These weak attractions are called hydrogen bonds. (slightly +) H H (slightly +) O Hydrogen bond Slightly positive charge Slightly negative charge (slightly )
9 Chemical Reactions 36 Figure 2.UN03 37 Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones. Such changes in the chemical composition of matter are called chemical reactions. 2 H 2 + O 2 2 H 2 O A simple example is the reaction between oxygen gas and hydrogen gas that forms water. Hydrogen gas Oxygen gas Water Reactants Products Chemical Reactions 38 Chemical reactions include reactants, the starting materials, and products, the end materials. Chemical reactions can rearrange matter but cannot create or destroy matter.