Chapter 2An understanding of chemistry is important because the interaction between atoms is one of the lowest levels of biological organization.Which is the smallest unit of organization?The basic unit of all forms of matter is the atomAtoms are made up of subatomic particles. The 3 most stable subatomic particles are: neutrons, protons, and electrons (see fig 2.1)Slide 6Slide 7A collection of atoms of the same type form an elementSlide 9Slide 10The atoms of a particular element may have different numbers of neutronsThe Electron OrbitalsSlide 13The chemical behavior of an atom is determined by the number of electrons in the outermost electron shell.An inert element:Slide 16Slide 17A reactive atom will try to fill the valence shell by interacting with other atoms. This interaction may result in two atoms forming a chemical bond.---A molecule is two or more atoms held together by chemical bonds. The smallest unit that retains the physical and chemical properties of a compound.If an atom has an almost empty or an almost full outer electron shell it is more likely to form an ion.A chemical bond is formed through:After sodium loses an electron, it is:Slide 23After chlorine gains an electron, it is:Slide 25Slide 26A covalent bond is a bond formed when two atoms share pairs of electrons.Slide 28---A nonpolar covalent bond is a covalent bond in which the sharing of the electron pair is equal. (see fig. 2.4a)Slide 30Electronegativity defined as an atom’s ability to attract and hold electrons. An indication of how much positive charge is in the nucleus. Assigned a numerical value. The higher the #, the more electronegative an atom is.---A Hydrogen bond is formed by the charge attraction when a hydrogen atom which is covalently bonded to one atom is attracted to a second atom. (see fig. 2.7)Slide 33WATER AND LIFEWhat kind of bonds hold the atoms of a single water molecule together?What kind of bonds form between water molecules?Some of the most biologically important polar covalent bonds are the bonds in water molecules.Slide 38Polar and ionic substances which are hydrophilic are easily dissolved in water.Nonpolar substances are hydrophobic.Slide 41Slide 42>>>Water Molecules Tend To Stick TogetherSlide 44Surface Tension-cohesion among water molecules at the surface of water.Slide 46>>>Acids and bases Water molecules can dissociate.Slide 48In pure water the number of H+ ions = the number of OH- ions---An acid is a proton donor, or a substance which increases the concentration of H+ in a solution.---pH scale is a scale used to measure the acidity of solutions.Pure water is neutral in pH because:Slide 53Slide 54Because the pH scale is a logarithmic scale, a change of one pH unit represents a tenfold change in the concentration of H+.Buffers Help Maintain a Constant pHBuffers function by accepting H+ ions from solution when they are in excess, and donating H+ ions to the solution when the supply is depleted.Without buffers such as bicarbonate or phosphate, which property would be directly affected?Water helps to moderate the effects of changes in temperature.---Specific heat is the amount of energy that must be absorbed or lost for one gram of matter to change its temperature by one degree Celsius.Water has a high heat of vaporization and cools surfaces as it evaporates.---Heat of vaporization is the quantity of heat a liquid must absorb for 1 gram to be converted to the gaseous state, or to evaporate.The “hottest” molecules, which have the highest kinetic energy leave the liquid. As a result the average temperature / kinetic energy of the liquid drops.When you sweat, what property of water is functioning to cool you off?Water has a high heat of fusion and freezes much slower than other liquids.Slide 66Chapter 2Atoms, Molecules, and LifeAn understanding of chemistry is important because the interaction between atoms is one of the lowest levels of biological organization.Which is the smallest unit of organization?•Cell•Atom•Organelle•OrganThe basic unit of all forms of matter is the atom ---atom is the smallest unit of matter that retains the physical and chemical properties of the element.Atoms are made up of subatomic particles. The 3 most stable subatomic particles are: neutrons, protons, and electrons (see fig 2.1)Helium (He)nnHydrogen (H)electronshellnucleuse-p+p+p+e-e-Fig. 2.1•Protons are positively charged particles found at the core, or nucleus, of the atom•Neutrons are uncharged particles found at the core, or nucleus, of the atom.•Electrons are light, negatively charged particles that orbit around the nucleus in electron shellsA collection of atoms of the same type form an element ---an element is a substance that can’t be broken down into other substances by chemical reactions. (see table 2-1)Helium (He)nne-p+p+e-The atomic weight of an element is the number of protons plus the number of neutronsThe atoms of a particular element may have different numbers of neutronsThis difference results in isotopes ---Isotopes are atoms of the same element which have different atomic weightsThe Electron Orbitals ---Electron orbitals are the three-dimensional space around the nucleus of an atom where an electron will be found.---The electron orbitals of an atom are arranged in electron shells based on their energy level.Fig. 2.2The chemical behavior of an atom is determined by the number of electrons in the outermost electron shell.An atom with an incomplete (partially full) electron shell is reactive whereas an atom with a full electron shell is inert, or not chemically active.An inert element:•Forms covalent bonds with itself.•Has a full outer electron shell. •Has an empty outer electron shell.•Does not react with other elements because it is unstable.The Hindenburg-1937Sodium atom (neutral)Na17p+11p+11nChlorine atom (neutral)18nClIf an atom has a vacancy in the outer electron shell, it will try to fill that vacancy or get rid of the “extra” electrons so the outer shell is full. Fig. 2.5A reactive atom will try to fill the valence shell by interacting with other atoms. This interaction may result in two atoms forming a chemical bond.---A chemical bond is an attraction that holds two atoms together.---A molecule is two or more atoms held together by chemical bonds. The smallest unit that retains the physical and chemical properties of a compound.Similar atoms-molecule-element Different atoms-molecule-compoundIf an atom has an almost empty or an almost
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