Life is a chemical process

Transcription

1 CHEMISTRY FOR LIFE

2 Life is a chemical process Relies on and is subject to chemistry Must obey the laws of physics

3 Biologists study Chemistry because all living things are made of matter. Matter undergoes chemical changes. Chemical changes are essential and intrinsic is all life processes.

4 LEVELS OF ORGANIZATION IN LIVING SYSTEMS The simplest level of organization in living systems is the chemical level, which is composed of atoms and molecules. 1. What is an atom? Atoms are the smallest units of matter. Molecules are the simplest structural unit of an 2. element What is or a compound molecule?.

5 element A substance made up of only 1 type of atom, that cannot be broken down by chemical changes. Each element has unique characteristic properties.

6 ATOMS OF DIFFERENT ELEMENTS COMBINE TO FORM COMPOUNDS.

7 ELEMENTS, ATOMS, AND MOLECULES Of the over 100 elements, only about 25 are vitally important to living things.

8 Trace elements are essential to life, but occur in very small amounts

9 Combinations (molecules) of: carbon, hydrogen, oxygen, and nitrogen Make up over 90% of the mass of living matter

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11 PROPERTIES OF WATER A special and important biological compound

12 WATER Water is the most abundant molecule in the human body. It makes up around 65% of the body s weight. It is the most critical molecule for life. A water molecule is composed of one atom of oxygen and two atoms of hydrogen held together by covalent bonds.

13 H O H

14 The structure of a water molecule give it very special properties that allows it to have a variety of unique and special characteristics.

15 SPECIAL PROPERTIES OF WATER. Polar- H bonding, adhesion and cohesion. High specific heat. Universal Solvent. High Surface Tension. Capillary action.

16 The shape of the water molecule and the atoms in it give water a special property called polarity. + This means that one end of the molecule is slightly positive while the other end is slightly negative.

17 Water is polar covalently bonded In living systems, polar covalent bonds are important because of the unique properties exhibited by molecules with these kinds of bonds.

18 POLARITY PROPERTIES Polarity gives water several special properties that are very useful for living organisms : COHESION ADHESION HYDROGEN BONDING

19 COHESION Water is attracted to other water. This is called cohesion. This is caused by hydrogen bonds that form between the slightly positive and negative ends of neighboring water molecules. This is the reason why water is found in drops; perfect spheres.

20 ADHESION Water can also be attracted to other materials. This is called adhesion. (Remember Adhesive tape picks up things)

21 SURFACE TENSION Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. Water Strider

22 UNIVERSAL SOLVENT The body contains many substances in solution. Water is so effective at dissolving substances that it is referred to as the universal solvent.

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24 What did you observe when you placed a drop of water onto a piece of wax paper? What shape was it? Why do you think it is this shape?

25 WHAT IS HAPPENING?! Water is not attracted to wax paper (there is no adhesion between the drop and the wax paper). Each molecule in the water drop is attracted to the other water molecules around it. This causes the water to pull itself into a shape with the smallest amount of surface area, a bead (sphere). All the water molecules on the surface of the bead are 'holding' each other together (cohesion).

26 COULD YOU FLOAT THE PAPER CLIP? Scientific Reason: surface tension water has the ability to support small objects. The hydrogen bonds between neighboring molecules cause a film to develop at the surface.

27 BREAKING THE SURFACE TENSION What happened when you added a drop of detergent? Scientific Reason? The detergent has phosphate in it. The phosphate attracts to the water molecules and breaks the surface tension.

28 ADHESION AND SOLUBILITY Lets see what happens to the ink on this paper towel if we stick just the bottom of the paper towel in the water. Predictions..

29 CAPILLARY ACTION Capillary action is related to the adhesive properties of water. Capillary action is when water moves up a cylinder.

30 What is happening with the straw demonstration? the water molecules are attracted to the straw molecules. When one water molecule moves closer to the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw.

31 MORE CAPILLARY ACTION Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water. This explains how a meniscus forms in a cylander.

32 Apply these properties to answer WHY the meniscus is different. glass plastic (wax)

33 PLANTS AND CAPILLARY ACTION Plants take advantage of capillary action to pull water from the soil into themselves. From the roots water is drawn through the plant by another force, transpiration.

34 SPECIFIC HEAT Water has a high heat capacity. Specific heat (a measure of heat capacity), is the heat required to raise the temperature of 1 gram of water 1 C. Water, with its high heat capacity, changes temperature more slowly than other compounds that gain or lose energy.

35 Water As a Habitat. Water s resistance to sudden changes in temperature makes it an excellent habitat (organisms adapted to narrow temperature ranges may die if the temperature fluctuates widely). The heat retaining properties of water provide a much more stable environment than is found in terrestrial situations. AND Fluctuations in water temperature occur very gradually (seasonal extremes are small).

36 The shape of the water molecule and the atoms in it give water a special property called polarity. This means that one end of the molecule is slightly positive while the other end is slightly negative.

37 UNIVERSAL SOLVENT The water of the body contains many substances in solution. In a solution one or more substances are dissolved. The dissolved substances are called solutes. The water which dissolves the solutes is called the solvent. Water is so effective at dissolving substances that it is referred to as the universal solvent. Notice how the negative ends of water attract sodium and the positive ends attract chloride.

38 Hydrophilic: Hydrophobic: Example: mix salad oil with water shake to break H bonds but as these bonds reform between water molecules, they push the oil molecules out of the way-the oil tends to cluster together in drops or as a layer on the water s surface-thereby exposing less surface area to the water

39 ELECTROLYTES Substances that form ions in solutions are called electrolytes. When electrolytes such as sodium chloride dissolve in water, their ions will conduct electricity through the solution. (A substance such as table sugar will not form ions in solution and will not conduct electricity.) A demonstration in class will allow you to see if a substance is an electrolyte or not.

40 A CLOSER LOOK AT WATER Inquiry lab

41 REVIEW! What s the matter?

42 ALL LIVING THINGS ARE MADE OF MATTER

43 What is matter? Matter is anything that occupies space and has mass

44 ALL MATTER IS MADE OF ATOMS.

45 THE ATOMS THAT MAKE UP EACH ELEMENT ARE UNIQUE FROM ONE ANOTHER.

46 THE ATOM Each atom is made up of smaller parts called protons, electrons and neutrons. Protons and neutrons are found in the central portion of the atom called the nucleus. Electrons are found in energy shells moving around the nucleus.

47 EACH ATOM HAS A SPECIFIC NUMBER OF PROTONS (AND ELECTRONS). In general: atoms are electrically neutral Meaning the # of protons (+) = # of electrons (-) Protons have a positive (+) electrical charge. Neutrons have no charge (are neutral). Electrons have a (-) negative electric charge.

48 THE NUMBER OF PROTONS DETERMINES AN ATOM S IDENTITY boron carbon nitrogen 5 protons 6 protons 7 protons

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50 Elements are arranged in the Periodic table based on their atomic number (# of protons) the atomic number identifies the element

51 ATOMS ARE ELECTRICALLY NEUTRAL # of protons = # of electrons Net electrical charge = 0

52 ELECTRONS Electrons are high energy particles with very little mass. They move around the nucleus of the atom at high speeds in different energy levels.

53 Electrons in outer levels have more energy than those in inner levels.

54 THE REACTIONS/ACTIONS OF ELEMENTS

55 A property of almost all elements is their ability to combine with other elements and form compounds* Hydrogen peroxide Glucose C 6 H 12 O 6 *the combination of two or more different elements.

56 In a compound, the different elements lose their individual chemical properties. For example, sodium is an explosive, dangerous substance. Chlorine is a highly poisonous gas. When the two are combined chemically they form sodium chloride, a nonpoisonous substance we commonly sprinkle on our food.

57 Compounds and Chemical Formula Compounds often have common names such as water or salt - but are also named by their formula which tell what elements make up the compound and in what proportion. For example, a molecule of water is made up of two hydrogen atoms for every one oxygen atom and is technically called dihydrogen monoxide. H 2 O

58 COMPOUNDS ARE REPRESENTED BY CHEMICAL FORMULAS 2 Cl Cl 2 2Cl 2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 Notice that the OH is a group The 2 refers to both H and O H O Ca O H

59 Electron number and arrangement determines how different elements will combine to form compounds.

60 HOW COMPOUNDS FORM

61 BONDING When an atom shares, gains or loses electrons to achieve an octet by partnering with another atom.

62 There are 2 main bond types: ionic and covalent In ionic bonding one atom has a stronger attraction for electrons than the other, and steals an electron from that atom In covalent bonding the attraction for electrons is similar for two atoms. They share their electrons to obtain an octet.

63 e - move around the nucleus in specific energy levels (shells) BOHR S MODEL

64 Each energy level (shell) is numbered starting closest to the nucleus. This is called the energy level s quantum number There is a max. # of electrons that each energy level can hold.

65 When you look at the Periodic Table, the energy levels of the atoms correspond to the groups (rows) of the table. The two elements in group 1, hydrogen and helium, are filling their first energy level. The eight elements of the second row are filling their second energy level.

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67 It is the outermost electrons that determine the chemical properties of the element. (very important)

68 *The electrons in the outermost (highest) E level.

69 These outermost electrons are the one s that are more likely to feel the presence of other atoms and hence the one s involved in bonding. Chemistry of an element depends almost entirely on the number of its valence electrons. (very important)

70 Atoms will gain or loose share Valence electrons to make a filled or empty outer most energy level.

71 Atoms bond to achieve stability reach a stable OCTET Atoms are the most stable when they fill their outermost energy level with 8 electrons*. * Special exception is H and He with only 2 electrons for a full 1 st energy level.

72 ELEMENTS BOND IN ORDER TO REACH AN OCTET IN THEIR VALENCE SHELL

73 ionization When an atom gains or loses an electron, the atom becomes charged what would the charge be on an atom that lost an electron? +1 (because your losing an electron) Gained two electrons? -2 (because you gain 2 electrons)

74 cation An ion is an atom that has either a net positive or net negative charge. anion

75 cation

76 IONS AND THE OCTET RULE Br I Ne K Ca gain or lose? how many? gain 1 gain 1 none lose lose 1 2 Ion Br P 3 none K 1+ Ca 2+ Elements will ionize (and bond) in order to achieve an octet in their valence shell.

77 Ions in families

78 Losing/gaining electrons is called ionization An ion is an atom that has either a net positive or net negative charge.

79 Electrons can be pulled out of the valence shell if an element with a larger attractive force* is near. *electron affinity

80 IONIC BONDING Ionic bonding involves 3 steps (3 energies) 1) loss of an electron(s) by one element, 2) gain of electron(s) by a second element, 3) attraction between positive and negative ions e 1) 2) Na 3) Cl Na + Na Cl +

81 Electron affinity as move across the periodic table

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83 The ratio of combining atoms results in a neutral compound Example: sodium and chlorine Na can loose 1 e-, sodium can gain 1 e- and they will both have achieved an octet in their valence shells SO.. They combine in a 1:1 ration and the resulting compound is [Na] + [Cl] - or NaCl What about calcium and fluorine? Calcium looses 2 e-, fluorine only gains 1 e- SO the ratio to get a neutral molecule must be 1 calcium atom: 2 fluorine atoms or CaF 2

84 3 BIOLOGICALLY IMPORTANT PROPERTIES OF IONIC COMPOUNDS Ionic compounds are soluble in water.

85 In aqueous solution, an ionic compound dissociates into its ions. (eg. when NaCl dissolves in water, the solution contains Na + ions and Cl ions.

86 The dissociated ions in aqueous solution give the solution the ability to conduct electricity.

87 ELECTROLYTES

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89 COVALENT BONDS A chemical bond that involves sharing a pair of electrons between neutral atoms in a molecule in order to achieve an octet in the valence shell.

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91 COVALENT bonds result from a strong interaction between atoms of similar electron affinity. Each atom donates an electron resulting in a pair of electrons that are SHARED between the two atoms

92 Generally, elements with similar electronegativity form covalent bonds

93 BIOLOGICALLY IMPORTANT PROPERTIES OF COVALENT BONDS A covalent bond STORES energy so breaking those bonds releases energy that can be used for the needs of living organisms.

94 In biological systems, covalent bonds are called strong bonds. This means that they are not normally broken under biological conditions. This is in opposition to weak bonds like ionic bonds which are easily broken under normal biological conditions of temperature and pressure. (very important)

95 Atoms can bond forming single, double, triple and even quadruple covalent bonds. ethene

96 The angles formed between covalently bonded atoms are specific and defined. This means that biological molecules formed with covalent bonds have definite and predicable shapes. (very important) glucose

97 O Structural formulas indicate kind, number and arrangement of bonds using a line to represent a shared e- pair H H

98 Don t forget when forming compounds, that ions combine in whole number ratios to achieve a neutrally charged compound.

99 PREDICTING TYPES OF BONDS How do you predict whether atoms will form ionic or covalent bonds? Notice the location of the elements in the Periodic Table. As a rule, elements on the right (non-metals) share electrons with each other (covalent bonds) and elements on the left tend to donate electrons to elements on the right (ionic bonds).

100 One word of warning: hydrogen behaves with a divided personality. While it is traditionally placed in the periodic table above lithium, there are good reasons to put it above fluorine instead (or as well). And remember: As with all generalizations, there are exceptions.

101 POLAR COVALENT BONDS Consider, carbon (C) and chlorine (Cl). Chlorine is clearly to the right of carbon. Carbon is however fairly central. Electrons in a bond between these two elements are shared (covalent), but they are not shared equally. The shared electrons (one from Cl, one from C) would spend more of their time under the influence of chlorine, being farther right, but are not completely lost to carbon (as they would be to sodium).

102 The electrons being shared are held closer to the Cl than to the C giving the molecules slightly charged areas.

103 POLAR AND NON-POLAR COVALENT BONDS There is a type of covalent bond called a polar covalent bond. In human body systems, polar covalent bonds are important because of the unique properties exhibited by molecules with these kinds of bonds.

104 The result of this pattern of unequal electron association is a charge separation in the molecule, where one part of the molecule has a partial negative charge and the other has a partial positive charge. (You should note this molecule is not an ion because there is no exchange of electrons, but there is a simple charge separation in this electrically neutral molecule.)

105 In addition to polar covalent bonds, there are nonpolar covalent bonds. In biological systems, if a molecules has a predominance of nonpolar covalent bonds, that substance is hydrophobic. (very important)

106 The interaction between polar and nonpolar molecules is very important in biological systems.

107 HYDROGEN BONDS

108 Electrons can be bumped up to a higher shell if hit by an electron or a photon of light.