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Unformatted text preview: Biology 1103 Lecture #3 Tuesday August 23, 2011 ATOM ATOM Smallest component of an element ELEMENT A substance consisting of atoms which all substance have the same number of protons - i.e. the same atomic number. Subatomic particles protons, neutrons, electrons – make up an atom Atomic number Number of protons. The number of protons equals the number of electrons. Atomic mass Mass of protons, neutrons and electrons (mainly protons and neutrons) Maximum number of electrons: shell # 123 2 (2) Helium 2+8 (10) Neon 2+8+8 (18) Argon Stable 2 2, 8 2, 8, 8 MOLECULE A combination of atoms Example: water H2 O methane CH4 glucose C6H12O6 Three Kinds of Bonds Covalent Ionic Hydrogen Covalent Bond – sharing electron pairs. Hydrogen molecule H2 Water molecule methane molecule Covalent Bond – Lewis dot diagram showing the sharing of electron pairs Structural formula. Carbon has four covalent bonds. Three-dimensional representations of: REACTANTS AND PRODUCTS Modeling Ammonia Valence of important atoms Hydrogen 1 Hydrogen Oxygen 2 Nitrogen 3 Carbon 4 Valence is the number of electrons needed to complete the outer shell. complete Ionic Bonds Results from the gain or loss of Results electron(s) electron(s) An Ion is an atom that has gained An or lost electrons , thus acquiring a charge charge Ionic bond NaCl Na+ Cl- Carbon is a versatile component of life’s molecules Carbon is the fourth most common element in the universe and the second most common element in your body. your Just six elements make up the bulk of you: Oxygen (65%) Carbon (18.5%) Hydrogen (9.5%) Nitrogen (3.3%) Phosphorus and sulfur (2%) Carbon is a key component of the molecules of living organisms because it can form multiple covalent bonds – strong chemical bonds resulting from the sharing of a pair of electrons between two atoms. two When atoms are linked by covalent bonds, they form molecules. Carbon atoms have four potential binding sites and can therefore bind up to four different atoms. different Organic molecules have carbon-based backbones and Organic at least one C-H bond. at HYDROGEN BOND Attraction between hydrogen atoms Attraction with a partial positive charge and an atom – like oxygen- with a partial negative charge negative Polar water molecule ISOTOPES Same atomic number but differ in atomic mass. Same i.e. they differ in the number of neutrons they have. have. Imaging the body with isotopes Free radical Properties of water All of life’s chemical reactions take place in All water, and many living things can survive only a few days without it. only Properties of water Water is a universal solvent (a substance in Water solvent which other substances can dissolve). Water transports all of life’s dissolved Water molecules, or solutes, from place to place, solutes from making life essentially a water-based solution. solution Properties of water Water is such a Water good solvent because it is a polar molecule – a polar molecule in which electrons are not shared equally between atoms, causing a partial negative charge at one end and a partial positive charge at the other. charge Properties of water Water is an excellent Water solvent for other polar molecules and substances that contain ionic bonds – strong ionic bonds formed between oppositely charged ions (an atom that has an electrical charge resulting from the loss or gain of electrons). or Properties of water Each water molecule Each has a partial charge on each end, so it can form electrostatic attractions, known as hydrogen bonds, with one another bonds with and with other molecules. molecules. Properties of water Water molecules can absorb a lot of energy Water before they get hot and vaporize (turn into a gas) because of their hydrogen bonds. gas) Ice floats because water is less dense as a Ice solid than as a liquid. solid Properties of water The different chemical The properties of water-based solutions reflect their pH – the pH concentration of hydrogen ions (H+) in a solution. (H pH ranges from 0 to 14. Properties of water Water molecules (H2O) can O) split briefly into separate hydrogen (H+) and hydroxide hydrogen and (OH-) ions. In pure water, (OH ions. the number of separated H+ the ions is exactly equal to the number of separated OHnumber ions, and the pH is therefore 7, or neutral. 7, Properties of water Acids have a higher Acids concentration of hydrogen ions (H+) and a pH closer to ions and 0. When acids are added to water, they increase the concentration of hydrogen ions and make the solution more acidic. more Properties of water Bases have a lower concentration of hydrogen ions (H+) hydrogen and a pH closer to 14. Bases remove H+ ions from a solution, thereby increasing the proportion of OHproportion ions. ions. Properties of water Strong acids and bases are highly reactive Strong with other substances, which makes them destructive to the molecules in a cell. Many biochemical reactions take place only at a certain pH. Living things are extremely sensitive to changes in pH, and most function best when their pH stays within a specific range. specific ...
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This note was uploaded on 09/08/2011 for the course BIOL 1103 taught by Professor Armstrong during the Spring '07 term at UGA.

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