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Chapter 2

Chapter 2- Water.docx

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Department
Biology
Course Code
BIO152H5
Professor
Fiona Rawle

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Chapter 2- Water and Carbon: The Chemical Basis of Life Chemical evolution: Early in earth’s history, simple chemical compounds in the atmosphere and ocean combined to form larger more complex substances. 2.1 Building Blocks of Chemical Evolution H, C, N, O make up 96 percent of all matter found in organisms today. -atomic number: protons. Subscript of each element -isotopes: forms of an element with different numbers of neutrons. -mass number: protons plus neutrons -orbital: electrons move around nuclei in specific regions. 2 electrons. Grouped into electron shells. -valence: number of unpaired electrons in an atom. -Atom is most stable when valence shell is filled. -covalent bonds: share electrons; form molecules. -nonpolar covalent bond: equal sharing of electrons. Symmetrical -polar covalent bonds: asymmetric sharing of electrons. Some atoms hold electrons in covalent bonds much more tightly than do other atoms—electronegativity. Electronegativities: O >> N > C= H Ionic bonds: electrons transferred. Gives resulting atom full shell. Cation- loses electron.Anion- gains -Mass of one mole of any molecule is the same as its molecular weight expressed in grams. Molecular weight is the sum of the mass numbers of all elements in a molecule. -Molarity is the number of moles of the substance present per litre of solution -Water is polar meaning the overall distribution of charge is asymmetrical. -ions and polar molecules are hydrophilic. Uncharged and nonpolar are hydrophobic. -Hydrogen bonding makes it possible for almost any charged or polar molecule to dissolve in water. -Properties of water 1. forms hydrogen bonds 2. solvent 3. cohesion- binding between like molecules. Water stays together because of hydrogen bonds between the molecules. 4. adhesion- Binding between unlike molecules. Water adheres to surfaces that have any polar or charged components. 5. surface tension- any force that depresses
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