Chapter 2 Chemistry of Life

Transcription

1 Chapter 2 Chemistry of Life 1

2 21- Atoms, Ions and Molecules An Atom is the smallest basic unit of matter. All atoms share the same basic structure. 2

3 Atoms consist of three types of particles: Protons, Neutrons and Electrons. 3

4 Protons and Neutrons form the center of the atom- the nucleus.the electrons (e-) Move around the outside of the nucleus. 4

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6 Protons are positive (+), neutrons are neutral, and electrons are negative (-). Atoms have an equal number of protons and electrons, so they are electrically neutral. 6

7 An element is one particular type of atom, and it cannot be broken down into a simpler substance. Ex. Hydrogen, calcium, helium, oxygen All atoms of the same element have the same number of protons. Ex. Oxygen has 8 protons, Hydrogen has 1 proton. 7

8 Electrons move in clouds called energy levels around the nucleus. The first energy level holds 2 electrons, the second energy level holds 8 electrons, and the third energy level holds 8 electrons. 8

9 Chlorine has 17 e- 9

10 Atoms are considered stable when they have a full energy level. Atoms are considered unstable (reactive) when they do not have a full energy level. 10

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13 Four Elements make up over 90% of organisms: Carbon Oxygen Nitrogen and Hydrogen! 13

14 A compound is a substance made of two or more different atoms bonded together. Ex. H 2 O, CO 2 14

15 An Ion is an atom that has gained or lost an electron. The ion has a charge, positive or negative. ex. H +, or Cl - 15

16 An atom will gain or lose electrons to have a full energy level. If they gain e-, they become more negative. If they lose e-, they become more positive. 16

17 Electrons can be transfered from one atom to another atom Ex. Na to Cl Na + and Cl - 17

18 Then a Ionic Bond can form. It is an attraction between two oppositely charged ions. Ex. Na + and Cl - NaCl 18

19 A Covalent bond is the sharing of a pair or e- between atoms. Ex. H 2 O Oxygen needs two more e-, each H needs one more e-, so oxygen shared with two Hydrogen. 19

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21 A molecule is two or more atoms held together by covalent bonds. Ex. H 2 O, O 2 21

22 O 2 molecule 22

23 2-2 Properties of Water 23

24 Cells of all organisms are mostly water. Water gives cells structure, and transports materials within organisms. All the process necessary for life take place in a watery (aqueous) environment. 24

25 Water is a polar molecule. One end in slightly negative (oxygen end) and one end is slightly positive. (hydrogen end) The e- in water are not equally shared. Overall, the water molecule has a neutral charge. 25

26 Polar Water Molecule 26

27 Polar Molecules form Hydrogen Bonds. A Hydrogen bond is an attraction between the + hydrogen atom and the atom of another molecule. 27

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29 Due to it s hydrogen bonds, water has some unique properties: 29

30 1. High Specific Heat- water resists changes in temperature. Water must absorbe a great deal of heat before it changes temperature. This helps regulate cell temperature. 30

31 2. Cohesion- water molecules are attracted to each other they stick together. They form drops of rain, water beads up on a window. They also form Surface tension- like the skin on the water. 31

32 A Waterstrider 32

33 3. Adhesion- water molecules are attracted to other molecules.water sticks to a glass- forms the meniscus in a graduated cylinder. Water is also pulled up the vessels in plants. 33

34 Meniscus 34

35 Water dissolves many substance. A solution is a mixture of substances that is equally mixed throughout. The solvent is the substance that is present in a greater amount. The solute is the substance that is dissolved in the solvent. 35

36 Ex. Saltwater Solution: Saltwater Solvent: water Solute: salt 36

37 Ionic compounds dissolve in water. Non-polar substances, like oils and fats, rarely dissolve in water. 37

38 Acids and Bases An Acid is a compound that releases a proton H+ when it dissolves. A Base is a compound that removes protons- H+ from a solution. 38

39 ph 0-14 Acids- below 7 Neutral 7 Bases- above 7 39

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41 Most organisms need to be near neutral, 7 ph. Buffers are compounds that can bind to H+ or release H+ to maintain Homeostasis. 41

42 Cells work best at a narrow ph range! 42