Elements and Compounds The Chemical Context of Life Sodium Chlorine! Sodium chloride! An element is a substance that cannot be broken down to other substances by chemical reactions A compound is a substance consisting of two or more elements in a fixed ratio Why it matters: Deficiencies Matter is organized in Elements and Atoms! Living organisms are composed of about 25 key elements! Elements are composed of atoms, which combine to form molecules Nitrogen deficiency! Iodine deficiency!
Properties of Matter Carbon, hydrogen, oxygen, and nitrogen Make up the bulk of living matter! Matter occupies space, has mass, is composed of elements! Elements cannot be broken down into simpler substances 92 naturally-occurring elements 15+ artificially-synthesized elements Proportions of Elements differ Subatomic particles: protons, neutrons, electrons Cloud of negative charge (2 electrons)! Electrons! Nucleus!
Atomic Structure! Atomic nucleus contains protons and neutrons! Electrons travel around nucleus in orbitals Atomic Mass is measured in daltons! Atomic mass = mass of protons + neutrons (electrons have insignificant mass) Proton = 1 dalton = 1.66 X 10-24 grams Neutron = 1 dalton Isotopes are Atoms of the same Element with different Amounts of Neutrons! Atoms of an element with differing numbers of neutrons! Differ in physical but not chemical properties Radioisotopes! Some isotope nuclei are unstable and break down (decay) Release particles of matter and energy (radioactivity)! Radioisotopes decay at a steady rate Used to estimate the age of organic material, rocks, fossils Used as tracers to label molecules in chemical reactions
Electrons! Electron are negatively charged! Number of electrons = number of protons! Electron mass = 1/1800 dalton Electron Orbitals! Electrons are found in regions of space called energy levels (shells)! Within each energy level, electrons are grouped into electron orbitals Electron Orbitals Electron Orbitals in the Periodic Table of Elements Electron orbitals! x! y! Hydrogen (H) First energy level Number of electrons in energy levels Atomic number Number of electrons (e ) Number of protons (p + ) Amount in living organisms Common elements Trace elements Elements not found Energy level 1 Energy level 2 Energy level 3 Helium (He) z! 1s orbital! 2s orbital! Three 2p orbitals! 1s, 2s, and 2p orbitals! Electron-shell diagrams! Lithium (Li) Beryllium (Be) Second energy level Boron (B) Carbon (C) Nitrogen (N) Oxygen (O) Fluorine (F) Neon (Ne) Sodium (Na) Magnesium (Mg) Third energy level Aluminum (Al) Silicon (Si) Phosphorus (P) Sulfur (S) Chlorine (Cl) Argon (Ar)
Periodic Table of the Elements Atoms form Molecules or Compounds through Chemical Bonds! Ionic Bonds! Covalent Bonds including Polar Covalent Bonds! Hydrogen Bonds! van der Waals Forces Valence electrons determine the chemical reactivity of an atom Ionic bonds are attractions between ions of opposite charge When atoms gain or lose electrons Charged atoms called ions are created Example: Sodium and chloride ions bond to form sodium chloride, table salt Ionic bonds extend in all directions Transfer of electron Cation Anion + Na + Cl Na Cl Na Cl Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl Chloride ion Sodium chloride (NaCl)
Covalent Bonds: sharing of Electrons Polar Covalent Bond: unequal sharing of Electrons! Water is a polar molecule Oxygen is more electronegative than hydrogen Hydrogen Bonds: Polar bonding between Hydrogen and an electronegative Atom Hydrogen Bonds are very important in life Hydrogen Bond! Weak bond, useful in stabilizing large biological molecules such as proteins
Van der Waals Forces: weak fleeting charges Van der Waals Forces are weak molecular interactions over short distances a. Gecko inverted on glass b. Gecko toe c. Setae on toe d. Pads on a seta Chemical reactions make and break chemical bonds! Chemical reactions lead to new arrangements of atoms! The starting molecules of a chemical reaction are called reactants! The final molecules of a chemical reaction are called products 2 H 2! O 2! 2 H 2 O! Reactants! Reaction! Products! Molecules with similar shapes can have similar biological effects Morphine fits and activates the endorphine receptor Carbon! Nitrogen! Natural endorphin! Hydrogen! Sulfur! Oxygen! Natural endorphin! Morphine! Morphine! Brain cell! Endorphin receptors! Structures of endorphin and morphine!