Chapter 4 The Chemical Basis of Life

4.1 Elements Matter: anything that occupies space and has mass Element: pure substance that cannot be broken down into other substances by chemical means –Ex. gold(Al), carbon(C), oxygen(O) –25 essential to life 96% of our body= oxygen, nitrogen, carbon, hydrogen 4% = calcium, phosphorous, potassium, sulfur, & others < 0.01% are Trace Elements like iodine and iron Compound: 2 or more elements –Ex. Carbon dioxide(CO 2 ), water(H 2 O)

4.2 Atoms atom: smallest possible particle of an element Subatomic particles – proton: single unit of positive electrical charge (+) – electron: negative electrical charge (-) – neutron: electrically neutral = no charge An element’s physical and chemical properties depend on the number and arrangement of its subatomic particles –Ex. Shiny luster of copper metal

Atom Structure Nucleus: central core composed of neutrons and protons Electron “cloud”: area in which the electrons travel –No exact path –Much larger than nucleus Atomic number: number of protons in an atom –Differentiates elements

Isotopes Isotope: an element that has the same number of protons but different number of neutrons –Can make an element radioactive – ex: 12 C = normal, 14 C =radioactive Radioactive Isotope: nucleus decays over time giving off radiation in the form of matter and energy – ex. Carbon dating

Energy Levels The structure of the atom determines how it reacts with other atoms –Based on electrons Electrons differ in the amount of energy they have and how tightly they are held by the protons Energy Levels –First level = lowest, nearest to nucleus –Most reactive when they have partially full energy levels

4.3 Chemical Bonds ionic bond: an atom transfers an electron to another atom – ex. NaCl ion: atoms that have become electrically charged as a result of gaining or losing electrons

Covalent Bonds covalent bonds: two atoms share electrons –Number of bonds formed= additional in highest level

Molecular Formulas molecule: 2 or more atoms held together by covalent bonds Chemical formula = number and types of atoms in a molecule – ex. H 2 O Structural formula= how atoms are linked by bonds Space-filling model= colored spheres

Chemical Reactions chemical reactions: bonds break or form new bonds which result in the formation of one or more new substances –Some absorb energy and some release more than they absorb reactants: starting material products: ending materials

4.4 Properties of Water ~70-95% in cells polar molecule: a molecule in which ends have opposite electric charge hydrogen bond: weak attraction between hydrogen and another slightly negative atom –Covalent bond DiCaprio Water Movie

Cohesion and Adhesion Hydrogen bonds between molecules of liquid water lasts only a few trillionths of a second –New form as old break cohesion: tendency of molecules of the same kind to stick to one another –Much stronger for water than other liquids –Water through plants –Surface tension: water molecules pulled tightly together at surface adhesion: attraction between unlike molecules –Capillary action

Temperature Moderation Better ability to resist temperature change than most other substances Thermal energy: total amount of energy associated with the random movement of atoms and molecules in a sample of matter –Warm to cold Temperature: measure of the average energy of random motion of the particles in a substance –Heating=breaks bonds –Cooling= forms H bonds

Low Density of Ice density: amount of matter in a given volume Ice is less dense than liquid water Hydrogen bonds keep molecules spaced evenly

Dissolve Substances solution: uniform mixture of two or more substances –Salt water solvent: the substance that dissolves the other substance and is present in great amounts –Water solute: the substance being dissolved –Salt aqueous solution (aq): water is the solvent Main solvent in cells, blood, & plant sap –Dissolves ionic compounds by attracting opposite charge and pulling apart (NaCl) –Dissolves nonionic compounds similarly eventhough there is only a slight charge (sugar)

Acids, Bases, and pH In some aqueous solutions, some water molecules break into ions –H + and OH - acid: a compound that donates H + to a solution –HCl = H + and Cl - base: a compound that removes H + ions pH scale: describes how acidic or basic a solution is –0 = most acidic –7 = neutral (pure water) –14 = most basic buffers: substances that cause a solution to resist changes in pH –Blood pH