Chapter 2 Chemistry of Life 1
21- Atoms, Ions and Molecules An Atom is the smallest basic unit of matter. All atoms share the same basic structure. 2
Atoms consist of three types of particles: Protons, Neutrons and Electrons. 3
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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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
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
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
Chlorine has 17 e- 9
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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Four Elements make up over 90% of organisms: Carbon Oxygen Nitrogen and Hydrogen! 13
A compound is a substance made of two or more different atoms bonded together. Ex. H 2 O, CO 2 14
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
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
Electrons can be transfered from one atom to another atom Ex. Na to Cl Na + and Cl - 17
Then a Ionic Bond can form. It is an attraction between two oppositely charged ions. Ex. Na + and Cl - NaCl 18
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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A molecule is two or more atoms held together by covalent bonds. Ex. H 2 O, O 2 21
O 2 molecule 22
2-2 Properties of Water 23
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
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
Polar Water Molecule 26
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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Due to it s hydrogen bonds, water has some unique properties: 29
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
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
A Waterstrider 32
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
Meniscus 34
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
Ex. Saltwater Solution: Saltwater Solvent: water Solute: salt 36
Ionic compounds dissolve in water. Non-polar substances, like oils and fats, rarely dissolve in water. 37
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
ph 0-14 Acids- below 7 Neutral 7 Bases- above 7 39
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Most organisms need to be near neutral, 7 ph. Buffers are compounds that can bind to H+ or release H+ to maintain Homeostasis. 41
Cells work best at a narrow ph range! 42