Chapter 2 Chemistry of Life 2-1 Composition of Matter -Mass- quantity of matter- use a balance to measure mass -Weight- pull of gravity on an object- use a scale Elements -cannot be broken down into simpler matter -made of one type of atom Four elements make up about 90% of the mass of organisms O, C, H, and N Periodic table -provides the chemical symbol -Atomic Number- the number of protons -Atomic mass- the number of protons and neutrons Atoms -the simplest particle that retains all the properties of that element Atomic structure -nucleus contains protons (+) and neutrons (neutral) Electrons (-) (abbreviated as e-) orbit the nucleus at various orbitals. Orbitals correspond to specific energy levels 1 P a g e
electron Energy levels e- in outer energy levels have more energy neutron -first level holds 2e- (1 orbital) -second level holds 8e- ( 4 orbitals) -a full energy level makes a stable atom (Happy atom) -an incomplete energy level makes a reactive atom. proton Isotopes -all atoms of an element have the same number of protons. -Atoms that have a different number of Neutrons are called isotopes. Ex. C 12 and C 14 Atoms can gain, lose or share electrons Compounds -made of atoms of two or more elements -NaCl and H 2 O are examples -Tendency to form compounds depends on e- in outer energy levels. Chemical reactions combine atoms in ways that make the atoms more stable. Chemical Bonds -attachments between atoms Covalent bonds -two atoms share one or more pairs of electrons. Ex. H 2 O page 33. O shares an electron with each H. H acquires a full energy level (2e-) and O acquires a 2 P a g e
full energy level (8e-). Molecules -simplest part of a substance -contains all properties of the substance -exists in a free state Ionic bonds -Ion- an atom or molecule with an electrical charge. (Na + ) -attraction between a positive and a negative ion -sodium (Na) gives an e- to Chlorine (Cl) Na Na +, Cl Cl - Na + + Cl - = NaCl 2-2 Energy Energy- ability to do work States of Matter Solid, liquid, gas -gas has the most movement of molecules -add of take away energy to change states of matter. 3 P a g e
Chemical Reactions -energy is absorbed or released when chemical bonds are broken and new bonds form. Reactants Products -the number of atoms must be balanced on both sides of the equation. -a reversible arrow ( )- reaction can go either direction. Exergonic reaction- net release of energy Endergonic reaction- net absorption of energy Activation Energy -the amount of energy needed to start a reaction Catalyst -lowers the activation energy (Often speeds up a reaction because less activation energy is required.) 4 P a g e
Enzymes -biological catalysts -they are very specific for each reaction -they are not used up by the reaction. Oxidation Reduction reactions (Redox reactions) -Reduction- a reactant gains an e-, it becomes more negative. -Oxidation- a reactant loses an e-, it becomes more positive. Redox reactions always occur together. 2-3 Water and Solutions Polarity In a water molecule, the O and H do not share the electrons equally. The O end has a slight negative charge ( δ - ), and the H end has a slightly positive charge ( δ + ). Polar Molecules -e- are unevenly shared. -has a slightly + and slightly end -the overall charge on the molecule is neutral. Solubility of Water -waters polarity dissolves many other substances- sugars, some proteins, and ionic compounds(ex. NaCl). -ionic compounds will dissociate in water. -this frees up the ions to participate in many biological reactions 5 P a g e
Hydrogen Bonding -bonds form between H atoms (+) in one molecule and the end in other molecules. -this causes water molecules to be attracted to each other. (page 40) -H bonds are weaker bonds -heat can break hydrogen bonds Cohesion and Adhesion Cohesion- attraction between particles of the same type (water to water) Cohesion causes surface tension Adhesion- attraction between unlike particles (water to glass) Capillarity- the attraction between molecules that allows the rise of the surface of a liquid when in contact with a solid ex. the meniscus in a graduated cylinder ) Adhesion, Cohesion and capillarity allow water to move up narrow tubes against the force of gravity. Very important to plants! Temperature Moderation -water has a high heat capacity- it must gain or lose a relatively large amount of heat for the temp. of the water to change. -energy must first break the H bonds holding the molecules together, -H 2 O helps keep cells at even temp. -the oceans help moderate the temp. of earth. 6 P a g e
Unlike most substances, solid water is less dense than liquid water. Because of H bonds, ice has a large amount of open space. Therefore, ice is less dense than water, and it floats in water. Page 42. Solutions Solution- one or more substances are evenly distributed in another substance Solute- substance dissolved in the solution Solvent- substance in which the solution is dissolved Example- Solution- soda Solute- sugar, flavorings, salt, CO 2, caffeine, color Solvent- water Concentration- the amount of solute in a fixed amount of solution. Ex. 5% NaCl solution, 5g of NaCl in 100 ml of solution Saturated solution - no more solute will dissolve -ex. Sugar in the bottom of a coffee cup. Aqueous solution 7 P a g e
-water is the solvent -very important to living things -cells are in an aqueous solution -most chemical reactions in living organisms occur in aqueous solutions. Acids and Bases Ionization of Water (Dissociation of Water) -breaking apart of water into two ions. H 2 O H + + OH - H + + H 2 O H 3 O + OH - is the hydroxide ion H 3 O + is the hydronium ion In pure water hydronium ions equal hydroxide ions Acids - more hydronium ions than hydroxide ions -often sour -highly corrosive Bases- -more hydroxide ions than hydronium ions -also called alkaline -often bitter 8 P a g e
ph Scale 0-14 0= very acidic 7= neutral 14= very alkaline -each step is a factor of 10 (ex. Vinegar (ph 3) has 10,000 times more hydronium ions than water, (ph 7) Buffers -they neutralize small amounts of acids or bases -very important for homeostasis because enzymes work at a specific ph. Enzymes function at very narrow ph ranges! 9 P a g e