Topic 1 Biochemistry(2).pdf - Introduction to Biochemistry — Valency and chemical bonds electronegativity types of chemical bonds water — Carbon

Topic 1 Biochemistry(2).pdf - Introduction to Biochemistry...

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Valency and chemical bonds electronegativity types of chemical bonds water Carbon carbon skeletons isomers Macromolecules monomers and polymers Biologically important macromolecules Carbohydrates Lipids Proteins Nucleic Acids Introduction to Biochemistry
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Valences for the major elements of organic molecules Recall: electron shells of atoms are “full” when they have the maximum number of electrons allowed for that shell. Shell 1: 2 Shell 2: 8 Shell 3: 8 …etc. Outermost shell is called the valence shell. Bonding capacity is called the atom s valence (how many more electrons the atom needs to fill that shell) .
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Covalent bonding in four molecules Covalent bonds can form between atoms of the same element or atoms of different elements. A compound is a combination of two or more different elements.
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Electronegativity Determines the distribution of electrons within a covalent bond Higher values indicate stronger attraction of electrons. Oxygen = 3.5 Nitrogen = 3.0 Sulfur & Carbon = 2.5 Phosphorus & Hydrogen = 2.1
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A nonpolar covalent bond, where the atoms have similar electro- negativities. Electrons are distributed equally (or more or less equally) between atoms. e.g. C-H (almost equal); O=O (equal) A polar covalent bond, where the atoms have dissimilar electro- negativities. Electrons are distributed unequally between atoms. e.g. H-O, C-O, H-N Electrons in covalent bonds between atoms of equal electronegativity have a greater potential energy than those between atoms with unequal electronegativity. (Think tug-of-war: which is easier to break?) Example: Covalent C — H bonds have greater potential energy than O — H or C — O bonds Has importance for another type of bond, the hydrogen bond. Electronegativity
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Polar covalent bonds in a water molecule Atoms in a molecule attract electrons to varying degrees. Electronegativity is an atom s attraction for the electrons in a covalent bond. The more electronegative an atom, the more strongly it pulls shared electrons toward itself. Example: water. Oxygen attracts the electrons it shares with hydrogen better than hydrogen because it is more electronegative.
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Hydrogen bonds between water molecules
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Surface tension is a measure of how hard it is to break the surface of a liquid Water has an unusually high surface tension due to hydrogen bonding between the molecules at the air-water interface and to the water below
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Water (H 2 O) Ammonia (NH 3 ) Hydrogen bond d + d- d + d + d + d + d- Another example of a hydrogen bond: between water and ammonia
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Na Sodium atom Cl Chlorine atom § Instead of sharing electrons, as in covalent bonds, sometimes atoms strip electrons from their bonding partners. § An example is the transfer of an electron from sodium to chlorine. § After the transfer of an electron, both atoms have charges.
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