Lecture 2 Outline of Last Lecture I. What is Biology?II. Unifying Themes of BiologyIII. Diversity and Unity in LifeOutline of Current Lecture I. MatterII. Structure and Behavior of AtomsIII. Electrons and Energy LevelsIV. Chemical BondsV. Chemical ReactionsCurrent LectureChapter 2 – Atoms, Molecules, and Chemical Bonds *basic inorganic chemistryI. Matter - takes up space and has mass  elements and compoundsa. Elements – can’t be broken down into other substances by normal chemical processes 1. Carbon (C)2. Oxygen (O)3. Hydrogen (H)4. Nitrogen (N)b. Compound – molecules made of more than 1 element in a fixed ratioEx: NaCl (Sodium Chloride)1. Sodium (Na) – explosive2. Chlorine (Cl) – poison gas*This is an example of an emergent property (lecture 1) because as the elements are mixed, which separately are dangerous, they become table salt. BIOL 101 1st EditionII. Structure and Behavior of Atoms – smallest amount of an elementa. ALL elements are alikeb. Each atoms has its own kind of atoms c. Atoms are made of subatomic particles:1. Proton – positive charge, weighs 1 Dalton, INSIDE nucleus (center)2. Neutron – no charge, weighs 1 Dalton, INSIDE nucleus (center)3. Electrons – negative charge, weighs 1/2000 of a Dalton, orbits AROUND nucleus4. Exs: H  1 proton, 1 electron; C  6 protons, 6 neutrons, 2 electronsd. Atomic Numbers: number of protons in an atom 1. Important because neutral atoms have the SAME number of protons and electrons2. Knowing the number of electrons will be important in this course3. Atomic number is written as a subscript (the lower left-hand corner)e. Atomic Mass: number of protons + number of neutrons1. Knowing the atomic mass is important in determining concentrations2. Atomic mass is written as a superscript (the upper left-hand corner)f. Isotopes – atoms of an element that have a DIFFERENT atomic mass with the SAME atomic number1. They have a different number of neutrons2. Radio isotopes – isotopes that are unstable that break down and release energy*Radioactive isotopes are helpful in biology, easily detectableIII. Electrons and Energy Levelsa. Electron orbital shells – this is where electrons are found orbiting the nucleus, and this concept has rules:1. Electrons fill up the closest shell first (1st – 2 electrons)2. Outer shells filled in order (2nd and 3rd hold 8)3. If the atom can’t fill all the shells, ONLY the outer shell is partially empty4. Octet rule – all atoms want to fill the outer shell completelyEx: noble elements (last column of periodic table) have all 8 electrons in the outer shellb. Chemical properties of an element depend on the number of electrons in the outermost shell because it determines how well they form:IV. Chemical Bonds: Attractions that hold atoms togethera. Valence – the bonding capacity of an atom = number of bonds an atom needs to become stable = number of electrons needed to fill the outer shellb. Strong Bonds – 1. Covalent bond *the most common bond in Biol 101* - formed by sharing electrons (very strong), 2 kinds:i. Nonpolar - when atoms have similar or identical electronegativity (the ability to attract electrons) share electronsii. Polar – shares electrons unequally, occurs when one atom has a very different electronegativity from the other, the ends of the bond are different (the one with more electronegativity is negatively charged, while the one with less is slightly positively charged), generally found in H with O, N, ClEx: H2O, H – positively charged, O – negatively chargediii. Polar and nonpolar molecules are NOT attracted to each otheriv. Single covalent bonds share 1 pair of electronsElement ValenceHydrogen (H) 1Oxygen (O) 2Nitrogen (N) 3Carbon (C) 4v. Double covalent bonds share 2 pairs of electronsvi. Triple covalent bonds share 3 pairs of electrons*Side note: electronegativity of common elements:Na – 0.9, H – 2.1, C – 2.5, N – 3.0, Cl – 3.0, O – 3.5 (very high)2. Ionic bonds – formed by electrostatic attraction between two atoms after a COMPLETE transfer of an electron from a donor atom to an acceptor atoms – NOT sharing – causes a strongcharge attractioni. Ex: NaCl (Sodium Chloride)Na – 1 valence electronCl – 7 valence electronsSodium loses its’ electron and becomes Na+ and Chlorine gains that electron becoming Cl--.c. Weak Bonds – some are important to Biol 1011. Hydrogen Bonds – weak charge attraction between a positively charged H atom of a molecule and a negatively charged atom of another atom, weak attraction between polar moleculesi. No electron sharingii. No electron transferiii. Weak bondiv. 1/20 strength of a covalent bondv. Continually breaking and reformingEx: H2O* Question on first exam – what is a Hydrogen bond? Draw H2O showing the polar bonds (shown above)This model demonstrates the slightly positive charges on both H atoms and the negative charge on the O atom frompulling the 2 valence electrons away from the H atoms. Use δ (lowercase delta) followed by a + or - to denote charges in polar molecules.2. Hydrophobic Bonds – nonpolar molecules avoid H2O (polar) and thus associate with each other, “afraid of water”, very little strength in this phenomenon, important in membrane structuresV. Chemical Reactions – breaking and forming of bondsa. Described by chemical equations that illustrate which atoms are involved, how many are involved, and which way the reaction goes.Ex: 3H2 + N2 ⇄ 2NH3*Side note: most biologically important reactions are REVERSIBLE and will eventually reach equilibrium (reaction times the same both