Ap Biology Ch. 2 Notes

AP Biology notes: Chapter 2- The Chemical Context of Life

1. Overview * The bombardier beetle fights the ants that plague it by using chemistry. * The natural systems and environment that organisms live in involves chemistry and physics. * Biology is not the only category of science. There is also chemistry, physics, and engineering. * Organization of life is separated into a hierarchy of structural levels. 2. Elements and Compounds * Matter- anything that takes up space and has mass. * Matter also exists in many different forms and has its own characteristics. It is also made up of elements. * Element- a substance that cannot by broken down to other substances by chemical reactions. * Compound- a substance consisting of two or more different elements combined in a fixed ratio. * Compounds have different properties from those of its elements. (Sodium by itself is a metal and chlorine is a poisonous gas. However, combined they made table salt. ) 3. Essential Elements of Life * About 25 of the 92 natural elements are essential to life. Carbon, oxygen, hydrogen, and nitrogen make up 96% of living matter, while phosphorus, sulfur, calcium, and potassium make up the remaining 4%. * Iodine deficiency caused by the lack of iodine causes the thyroid gland to grow to abnormal size. This medical condition is called goiter. * Trace elements- those required by an organism in only small quantities. Ex: Iron and Iodine 4. Subatomic particles * Atom- smallest unit of matter that still retains the properties of an element. * Three types of subatomic particles: neutrons, protons, and electrons. * Electrons travel nearly at the speed of light, forming a cloud around the nucleus. * Dalton is a measurement used to measure subatomic particles. (same as atomic mass unit or amu) * Neutrons and protons weight about 1 Dalton. * Electrons weight so less that they do not contribute in the total mass of an atom 5. Atomic number and atomic mass * Atomic number- number of protons in an element. * Mass number- sum of protons and neutrons. * Atomic mass- the total average mass of an atom. * Atomic mass is concentrated mostly in the nucleus. 6. Isotopes * Isotopes- atoms of the same element that have different numbers of neutrons. * If an isotope is unstable, they have the tendency to lose particles. They become radioactive. * Radioactive isotope- one in which the nucleus decays spontaneously, giving off particles and energy. Eventually, the nucleus decays to an extent where it loses enough protons to form a different element. * Radioactive isotopes are useful as tracers to follow the process of metabolism, important diagnostic tools in medicine, and in sophisticated imaging instruments. 7. The energy levels of electrons * Atoms are mostly empty space. * Only electrons are directly involved in chemical reactions. * An atom’s electrons vary in the amount of energy they possess. * Energy- capacity to cause change * Potential energy- the energy that matter possesses because of its location or structure. * Matter usually moves to the state of the lowest potential energy. * Energy levels(shells)- different states of potential energy that electrons have in an atom * Electrons can change energy levels but only by the loss or gain of energy. * Energy is lost in the form of heat 8. Electron configurations and chemical properties * Electron configuration- the distribution of electrons in the atom’s electron shells. * First Shell- can hold 2 electrons maximum * Second shell- can hold 8 electrons maximum * Valence electrons- electrons that are in the outermost electron shell. (valence shell) * An atom is unreactive if it has a completed valence shell. 9. Electron orbitals * Orbital- the most common 3D-space in which an electron spends its time. * First electron shell- one spherical “s” orbital * Second electron shell- 4 orbitals; one large “S” orbital and three “p” orbitals (2s and 2p) 10. Covalent Bonds * Chemical bonds- covalent or ionic bonds * Covalent bonds- sharing of a pair of valence electrons by two atoms. * Molecule- two or more atoms held together by a covalent bond. * Single bond- one pair of shared electrons * Structural formula- formula that represents both atoms and bonding * Molecular formula- formula that indicates the different types of atoms in a molecule * Double bond- two pairs of shared valence electrons * Electronegativity- the attraction of a particular kind of atom for the electrons of a covalent bond * Nonpolar covalent bond- electrons shared equally * Polar covalent bond- electrons shared unequally * Water: has a partial negative charge on the oxygen and a partial positive charge on the two hydrogens. 11. Ionic bonds * Cation- positively chared ion * Anion- negatively charged ion * Ionic bond- the attraction between cations and anions * Ionic compounds(salts)- compounds formed by ionic bonds. * Salts often form crystals. * A convalent molecule has a definite size and number of atoms, when an ionic molecule does not. * Some salts must lose or gain electrons to balance the number of cations and anions. * Environment also affects the strength of ionic bonds. 12.Weak chemical bonds * Convalent bonds are the strongest * Hydrogen bonds and van der waals interactions are weak bonds. * Hydrogen bonds when a hydrogen atomcovalently bonded to one electronegative atom is also attracted to another electronegative atom. * Van der Waals interactions are weak because they only form when atoms and molecules are very close together. * Proteins can also form hydrogen bonds, ionic bonds, and other weak bonds. 13. Molecular shape and function * a molecule that consists of two atoms are linear * a molecule that consists of more than two atoms are bent. 14. Chemical reactions make and break chemical bonds * chemical reactions-making and breaking of chemical bonds * reactants- starting materials in an chemical equations * products- end result of the chemical equation * chemical equilibrium- the point at which the reactions offset one another exactly and at the same rate.