Basic Chemistry for Biology. Honors Biology

Transcription

1 Basic Chemistry for Biology Honors Biology

2 Composition of Matter Matter - Everything in universe is composed of matter Matter is anything that occupies space or has mass Mass quantity of matter an object has Weight pull of gravity on an object

3 Elements Pure substances that cannot be broken down chemically into simpler kinds of matter More than 115 elements (92 naturally occurring)

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5 Periodic Table Elements are arranged by their atomic number on the Periodic Table The horizontal rows are called Periods & tell the number of energy levels Vertical groups are called Families & tell the outermost number of electrons

6 Over 90% of the mass of an organism is composed of 6 elements (carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur)-chnops Each element has unique chemical symbol Consists of 1-2 letters First letter is always capitalized

7 Atoms The simplest particle of an element that retains all the properties of that element Properties of atoms determine the structure and properties of the matter they compose

8 The Nucleus Nucleus (central core) consists of positive charged protons and neutral neutrons Positively charged Contains most of the mass of the atom

9 The Protons= positive charge All atoms of a given element have the same number of protons Number of protons called the Atomic Number (ex: Oxygen has an atomic number of 8 has 8 protons in its nucleus

10 The Neutrons Neutral Charge (no charge) The number can vary slightly among atoms of the same element Different number of neutrons produces isotopes of the same element

11 Atomic Mass The atomic mass of an atom is found by adding the number of protons & neutrons in an atom The electrons add a negligible mass to the atom

12 The Electrons Have a negative charge High energy particles with little or no mass Travel at very high speeds randomly at various distances (energy levels) from the nucleus Involved with making chemical bonds

13 Atoms have energy levels or electron clouds The 1 st level can only hold 2 electrons The other levels can hold 8 electrons Atoms want to have full outer shells

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19 Mass Number The mass number of an atom is the total number of protons and neutrons 19

20 Isotopes. Different atoms of an element that have the same number of protons but different numbers of neutrons are called 20

21 Stable isotopes doe not change their nuclear structure over time. Certain isotopes called radioactive isotopes are unstable because their nuclei decay to form a simpler and thus more stable configuration. 21

22 Radioactive isotopes can be used to study both the structure and function of particular tissues 22

23 Compounds Most elements do not exist by themselves. Elements readily combine with other elements in a predictable fashion A compound is a pure substance made up of atoms of two or more elements The proportion of atoms are always fixed

24 A Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound H 2 O

25 Molecules are the simplest part of a substance that retains all of the properties of the substance and exists in a free state Some molecules are large and complex

26 Compounds vs. Molecules A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. All compounds are molecules but not all molecules are compounds. Molecular hydrogen (H 2 ), molecular oxygen (O 2 ) and molecular nitrogen(n 2 ) are not compounds because each is composed of a single element.

27 FYI Water (H 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) are compounds because each is made from more than one element. The smallest bit of each of these substances would be referred to as a molecule. For example, a single molecule of molecular hydrogen is made from two atoms of hydrogen while a single molecule of water is made from two atoms of hydrogen and one atom of oxygen.

28 Chemical Formulas Subscript after a symbol tell the number of atoms of each element H 2 0 has 2 atoms of hydrogen & 1 atom of oxygen Coefficients before a formula tell the number of molecules 3O 2 represents 3 molecules of oxygen or (3x2) or 6 atoms of oxygen

29 The tendency of elements to combine and form compounds depends on the number and arrangement of electrons in their outermost energy level Atoms are most stable when their outer most energy level is filled

30 Most atoms are not stable in their natural state Tend to react (combine) with other atoms in order to become more stable (undergo chemical reactions) In chemical reactions bonds are broken; atoms rearranged and new chemical bonds are formed that store energy

31 Covalent Bonds Formed when two atoms share one or more pairs of electrons

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34 Covalent bonds may be nonpolar or polar. In a nonpolar covalent bond, atoms share the electrons equally; Polar one atom does not attract the shared electrons more strongly than the other atom 34

35 In a polar covalent bond, the sharing of electrons between atoms is unequal; one atom attracts the shared electrons more strongly than the other. 35

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37 Ionic Bonds Some atoms become stable by losing or gaining electrons Atoms that lose electrons are called positive ions Atoms that gain electrons are called negative ions

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40 Hydrogen Bond In a hydrogen bond, two other atoms (usually oxygen or nitrogen) associate with a hydrogen atom Hydrogen bonds are weak and cannot bind atoms into molecules. They serve as links between molecules. 40

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42 Solutions A solution is a mixture in which 2 or more substances are uniformly distributed in another substance

43 Solute is the substance dissolved in the solution Particles may be ions, atoms, or molecules Solvent is the substance in which the solute is dissolved Water is the universal solvent

44 Dissociation of water Breaking apart of the water molecule into two ions of opposite charge H 2 O H + (hydrogen ion) + OH - (hydroxide ion)

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46 Acids and Bases One of the most important aspects of a living system is the degree of acidity or alkalinity

47 Acids / Acidity High concentration of H+ (hydrogen) ions in solution HCl H + + Cl -

48 Bases / Basic / Alkalinity Less H+ ions in solution, more OH- (hydroxide) ions NaOH Na + + OH -

49 ph Scale Logarithmic scale for comparing the relative concentrations of hydrogen ions in a solution Ranges from 0 to 14 Each ph is 10X stronger than next e.g. ph 1 is 10 times stronger than ph 2

50 The Ph Scale 0-6.9= acid: more H+ ions 7 = neutral: equal amounts of H+ & OH- ions = base: less H+ ions and more OH- ions

51 the lower the ph the stronger the acid The more H+ ions the lower the ph and the stronger the acid the higher the ph the stronger the base The more OH- ions the higher the ph and the stronger the base ph 7.0 is neutral

52 ph Scale Principle: H + ion concentration and ph relate inversely. OH - ion concentration and ph relate directly.

53 Buffers Control of ph is very important Most enzymes function only within a very narrow ph Control of ph is accomplished with buffers made by the body Buffer the ph slayer!! Buffers keep a neutral ph

54 Buffers neutralize small amounts of either an acid or base added to a solution Complex buffering systems maintain the ph values of your body s many fluids at normal and safe levels

55 Buffering Systems in the Body

56 Bicarbonate Buffer System Is a mixture of carbonic acid (H 2 CO 3 ) and its salt, sodium bicarbonate (NaHCO 3 ) If strong acid is added: Hydrogen ions released combine with the bicarbonate ions and form carbonic acid (a weak acid) The ph of the solution decreases only slightly If strong base is added: It reacts with the carbonic acid to form sodium bicarbonate (a weak base) The ph of the solution rises only slightly

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58 Protein Buffer System Plasma and intracellular proteins are the body s most plentiful and powerful buffers Some amino acids of proteins have: Free organic acid groups (weak acids) Groups that act as weak bases (e.g., amino groups) Amphoteric molecules are protein molecules that can function as both a weak acid and a weak base

59 Physiological Buffer Systems The respiratory system regulation of acid-base balance is a physiological buffering system There is a reversible equilibrium between: Dissolved carbon dioxide and water Carbonic acid and the hydrogen and bicarbonate ions CO 2 + H 2 O «H 2 CO 3 «H + + HCO 3 When hyperventilation or rising plasma H + occurs: Deeper and more rapid breathing expels more carbon dioxide Hydrogen ion concentration is reduced Alkalosis causes slower, more shallow breathing, causing H + to increase Respiratory system impairment causes acid-base imbalance (respiratory acidosis or respiratory alkalosis)

60 CHEMICAL REACTIONS A chemical reaction occurs when new bonds are formed or old bonds break between atoms The starting substances of a chemical reaction are known as reactants or. The ending substances of a chemical reaction are the products. 60

61 Many chemical reactions are very complex involving multistep sequences called biochemical pathways

62 Most chemical reactions require energy to begin The amount of energy needed to start the reaction is called activation energy

63 Certain chemical substances (catalysts) reduce the amount of activation energy required Biological catalysts are called enzymes