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Chapter 2 • All living beings are organized. The smallest part of a living organism is the atom. Atoms are the smallest part of an element. An element is a pure substance. • There are 25 different elements necessary to life can be classiffied into: SPONCH (98%) and Trace elements (elements that the body needs in small amounts). • The smallest particle of an element is an atom. Different elements have different types of atoms. • Atoms of each element are distinguished by a specific number of protons or Atomic number. • The sum of protons and neutrons produce the Atomic mass (weight) of the element. • Atoms of the same element with different number of neutrons are called isotopes and some isotopes are radioactive. Electron arrangement determines the chemical properties of an atom • Electrons are arranged in shells. • The outermost shell determines the chemical properties of an atom. • These shells are called “energy shells”. 4e2e- 6p+ 6n Carbon (C) 6e2e- 8p+ 8n Oxygen (O) 5e8e2e- 15p+ 16n Phosphorus (P) 2e8e8e2e- 20p+ 20n Calcium (Ca) • Atoms whose shells are not full tend to interact with other atoms and gain, lose, or share electrons Outermost electron shell (can hold 8 electrons) Electron HYDROGEN (H) Atomic number = 1 First electron shell (can hold 2 electrons) CARBON (C) Atomic number = 6 NITROGEN (N) Atomic number = 7 OXYGEN (O) Atomic number = 8 Ionic bonds are attractions between ions of opposite charge • When atoms gain or lose electrons, charged atoms called ions are created • An electrical attraction between ions with opposite charges results in an ionic bond + Na Cl Na Sodium atom Cl Chlorine atom Na Na+ Sodium ion – Cl Cl– Chloride ion Sodium chloride (NaCl) Sodium atom (neutral) Chlorine atom (neutral) Sodium ion (+) Chloride ion (-) Covalent bonds, the sharing of electrons, join atoms into molecules • Some atoms share outer shell electrons with other atoms, forming covalent bonds – Atoms joined together by covalent bonds form molecules • Molecules can be represented in many ways The Molecule of Water Like no other common substance, water exists in nature in all three physical states: – as a solid – as a liquid – as a gas Why Is Water So Important to Life? • 1. Water Molecules Tend to Stick together. Figure 2.7 Cohesion among water molecules (p. 23). • Due to hydrogen bonding, water molecules can move from a plant’s roots to its leaves 2. Water’s hydrogen bonds moderate temperature Water is able to absorb a great deal of heat energy without a large increase in temperature and as it cools, a slight drop in temperature releases a large amount of heat 3. Evaporative cooling. A water molecule takes a large amount of energy with it when it evaporates This leads to evaporative cooling 4. Water is a versatile solvent • Solutes whose charges or polarity allow them to stick to water molecules dissolve in water – They form aqueous solutions Na+ – Na+ – + Cl– + + – Cl– – + Ions in solution – Salt crystal INTRODUCTION TO ORGANIC COMPOUNDS AND THEIR POLYMERS • Life’s structural and functional diversity results from a great variety of molecules. • In addition to water, all other biological molecules are organic or carbon based molecules. • A carbon atom forms four covalent bonds and it can join with other carbon atoms to make chains or rings Structural Ball-and-stick Space-filling formula model model Methane The 4 single bonds of carbon point to the corners of a tetrahedron. Life’s molecular diversity is based on the properties of carbon • A carbon atom forms four covalent bonds and it can join with other carbon atoms to make chains or rings. Carbon skeletons vary in many ways . ¾Organic molecules are characterized by having a central “backbone” made of atoms of carbon linked to each other like a “chain” of carbon atoms. In addition, other atoms can link to the carbon backbone • Carbon skeletons vary in many ways Ethane Propane Carbon skeletons vary in length. Butane Isobutane Skeletons may be unbranched or branched. 1-Butene 2-Butene Skeletons may have double bonds, which can vary in location. Cyclohexane Benzene Skeletons may be arranged in rings. Figure 3.1, bottom part • Organic molecules are characterized by having a central “backbone” made of atoms of carbon linked to each other like a “chain” of carbon atoms. Other atoms can link to the carbon backbone • There are 4 main types of biomolecules: Carbohydrates Lipids Proteins Nucleic Acids. Chemical reactions rearrange matter • In a chemical reaction: – reactants interact – atoms rearrange – products result 2 H2 + O2 → 2 H2O – Living cells carry out thousands of chemical reactions that rearrange matter in significant ways Beta-carotene Figure 2.17B Vitamin A (2 molecules)