An Introduction to the Chemical Level of Organization Chemistry Is the science of change Topics of this chapter include: The structure of atoms The basic chemical building blocks How atoms combine to form increasingly complex structures
2-1 Atoms and Atomic Structure • Matter • Is made up of atoms • Atoms join together to form chemicals with different characteristics • Chemical characteristics determine physiology at the molecular and cellular levels
2-1 Atoms and Atomic Structure • Subatomic Particles • Proton • Positive charge, 1 mass unit • Neutron • Neutral, 1 mass unit • Electron • Negative charge, low mass
2-1 Atoms and Atomic Structure • Atomic Structure • Atomic number • Number of protons • Nucleus • Contains protons and neutrons • Electron cloud • Contains electrons
Electron shell Hydrogen-2,deuterium Hydrogen-3,tritium Hydrogen-1mass number: 1 mass number: 3 mass number: 2 A typical hydrogennucleus contains aproton and no neutrons. A tritium (3H) nucleus contains a pair ofneutrons in additionto the proton. A deuterium (2H)nucleus contains aproton and a neutron.
2-1 Atoms and Atomic Structure • Elements and Isotopes • Elements are determined by the atomic number of an atom • Remember atomic number = number of protons • Elements are the most basic chemicals
2-1 Atoms and Atomic Structure • Elements and Isotopes • Isotopes are the specific version of an element based on its mass number • Mass number = number of protons plus the number of neutrons • Only neutrons are different because the number of protons determines the element
2-1 Atoms and Atomic Structure • Atomic Weights • Exact mass of all particles • Measured in moles • Average of the mass numbers of the isotopes
2-1 Atoms and Atomic Structure • Electrons and Energy Levels • Electrons in the electron cloud determine the reactivity of an atom • The electron cloud contains shells, or energy levels that hold a maximum number of electrons • Lower shells fill first • Outermost shell is the valence shell, and it determines bonding • The number of electrons per shell corresponds to the number of atoms in that row of the periodic table • Fun Video Time: • http://www.sciencekids.co.nz/videos/chemistry/molecules.html
Figure 2-2 The Arrangement of Electrons into Energy Levels The first energy levelcan hold a maximum oftwo electrons. Helium, HeAtomic number: 2Mass number: 4(2 protons 2 neutrons)2 electrons Hydrogen, HAtomic number: 1Mass number: 11 electron
Figure 2-2 The Arrangement of Electrons into Energy Levels The second and thirdenergy levels caneach contain up to 8electrons. Lithium, LiAtomic number: 3Mass number: 6(3 protons 3 neutrons)3 electrons Neon, NeAtomic number: 10Mass number: 20(10 protons 10 neutrons)10 electrons
2-2 Molecules and Compounds • Chemical Bonds • Involve the sharing, gaining, and losing of electrons in the valence shell • Three major types of chemical bonds • Ionic bonds • Attraction between cations (electron donor and positively charged) and anions (electron acceptor and negatively charged) • Covalent bonds • Strong electron bonds involving shared electrons • Hydrogen bonds • Weak polar bonds based on partial electrical attractions
2-2 Molecules and Compounds • Chemical Bonds • Form molecules and/or compounds • Molecules • Two or more atoms joined by strong bonds • Compounds • Two or more atoms OF DIFFERENT ELEMENTS joined by strong or weak bonds • Compounds are all molecules, but not all molecules are compounds • H2 = molecule only H2O = molecule and compound
2-2 Molecules and Compounds • Ionic Bonds • One atom—the electron donor—loses one or more electrons and becomes a cation, with a positive charge • Another atom—theelectronacceptor—gains those same electrons and becomes an anion, with a negative charge • Attraction between the opposite charges then draws the two ions together
Figure 2-3a The Formation of Ionic Bonds 1 3 2 Formation of ions Attraction betweenopposite charges Formation of anionic compound Sodium atom Sodium ion (Na) Sodium chloride (NaCl) Chlorine atom Chloride ion (Cl) Formation of an ionic bond. A sodium (Na) atom loses an electron, which is accepted by a chlorine (Cl) atom. Because the sodium (Na) and chloride (Cl) ions have opposite charges, they are attracted to one another. The association of sodium and chlorideions forms the ionic compound sodium chloride.
Figure 2-3b The Formation of Ionic Bonds Chloride ions(Cl) Sodium ions(Na) Sodium chloridecrystal. Largenumbers of sodium andchloride ions form acrystal of sodiumchloride (table salt).
2-2 Molecules and Compounds • Covalent Bonds • Involve the sharing of pairs of electrons between atoms • One electron is donated by each atom to make the pair of electrons • Sharing one pair of electrons is a single covalent bond • Sharing two pairs of electrons is a double covalent bond • Sharing three pairs of electrons is a triple covalent bond
Figure 2-4 Covalent Bonds in Four Common Molecules Electron Shell Model andStructural Formula Molecule Hydrogen(H2) HH OO Oxygen(O2) Carbondioxide(CO2) OCO Nitricoxide(NO) NO
2-2 Molecules and Compounds • Covalent Bonds • Nonpolar covalent bonds • Involve equal sharing of electrons because atoms involved in the bond have equal pull for the electrons • Polar covalent bonds • Involve the unequal sharing of electrons because one of the atoms involved in the bond has a disproportionately strong pull on the electrons • Form polar molecules — like water
Figure 2-5 Polar Covalent Bonds and the Structure of Water Hydrogen atom Hydrogen atom Oxygen atom Hydrogen atom Oxygen atom 2
2-2 Molecules and Compounds • Hydrogen Bonds • Bonds between adjacent molecules, not atoms • Involve slightly positive and slightly negative portions of polar molecules being attracted to one another • Hydrogen bonds between H2O molecules cause surface tension • Video showing covalent and ionic bonding: • http://www.youtube.com/watch?v=X9FbSsO_beg&list=PL857CFC8038F293CD
2-2 Molecules and Compounds • States of Matter • Solid • Constant volume and shape • Liquid • Constant volume but changes shape • Gas • Changes volume and shape
2-2 Molecules and Compounds • Molecular Weights • The molecular weight of a molecule is the sum of the atomic weights of its component atoms • H = approximately 1 • O = approximately 16 • H2 = approximately 2 • H2O = approximately 18
2-3 Chemical Reactions • In a Chemical Reaction • Either new bonds are formed or existing bonds are broken • Reactants • Materials going into a reaction • Products • Materials coming out of a reaction • Metabolism • All of the reactions that are occurring at one time
Figure 2-7 Chemical Notation Atoms The symbol of an element indicates one atom of that element. A number preceding the symbol of an element indicates more than one atom of that element. CHEMICAL NOTATION VISUAL REPRESENTATION one atomof hydrogen one atomof oxygen one atomof oxygen one atomof hydrogen two atomsof hydrogen two atomsof oxygen two atomsof hydrogen two atomsof oxygen
Figure 2-7 Chemical Notation Molecules A subscript following the symbol of an element indicates a molecule with that number of atoms of that element. VISUAL REPRESENTATION CHEMICAL NOTATION hydrogen molecule oxygen molecule hydrogenmolecule oxygenmolecule composed of twohydrogen atoms composed of twooxygen atoms water molecule composed of two hydrogen atoms and one oxygen atom water molecule
Figure 2-7 Chemical Notation Reactions In a description of a chemical reaction, the participants at the start of the reaction are called reactants, and the reaction generates one or more products. An arrow indicates the direction of the reaction, from reactants (usually on the left) to products (usually on the right). In the following reaction, two atoms of hydrogen combine with one atom of oxygen to produce a single molecule of water. VISUAL REPRESENTATION CHEMICAL NOTATION Balanced equation Chemical reactions neither create nor destroy atoms; they merely rearrange atoms into new combinations. Therefore, the numbers of atoms of each element must always be the same on both sides of the equation for a chemical reaction. When this is the case, the equation is balanced. Unbalanced equation
Figure 2-7 Chemical Notation Ions A superscript plus or minus sign following the symbol of an element indicates an ion. A single plus sign indicates a cation with a charge of 1. (The original atom has lost one electron.) A single minus sign indicates an anion with a charge of 1. (The original atom has gained one electron.) If more thanone electron has been lost or gained, the charge on the ion is indicated by a number preceding theplus or minus sign. VISUAL REPRESENTATION CHEMICAL NOTATION sodium ion chloride ion calcium ion chloride ion sodium ion calcium ion the calcium atom has losttwo electrons the sodiumatom has lostone electron the chlorineatom has gainedone electron A sodium atombecomes a sodium ion Electron lost Sodiumion (Na) Sodiumatom (Na)
2-3 Chemical Reactions • Basic Energy Concepts • Energy • The power to do work • Work • A change in mass or distance • Kinetic energy • Energy of motion • Potential energy • Stored energy • Chemical energy • Potential energy stored in chemical bonds
2-3 Chemical Reactions Types of Chemical Reactions Decomposition reaction (catabolism) Synthesis reaction (anabolism) Exchange reaction Reversible reaction
2-3 Chemical Reactions • Decomposition Reaction (Catabolism) • Breaks chemical bonds • AB A + B • Hydrolysis A-B + H2O A-H + HO-B • Synthesis Reaction (Anabolism) • Forms chemical bonds • A + B AB • Dehydration synthesis (condensation reaction) A-H + HO-B A-B + H2O
2-3 Chemical Reactions • Exchange Reaction (Also called Displacement) • Involves decomposition first, then synthesis • AB + CD AD + CB
2-3 Chemical Reactions • Reversible Reaction • A + B AB • At equilibrium the amounts of chemicals do not change even though the reactions are still occurring • Reversible reactions seek equilibrium, balancing opposing reaction rates • Add or remove reactants • Reaction rates adjust to reach a new equilibrium
2-4 Enzymes • Chemical Reactions • In cells cannot start without help • Activation energy is the amount of energy needed to get a reaction started • Enzymes are protein catalysts that lower the activation energy of reactions
2-4 Enzymes • Exergonic (Exothermic) Reactions • Produce more energy than they use • Endergonic (Endothermic) Reactions • Use more energy than they produce
Chemical Reaction Videos! • Major Chemical Reactions: • http://www.youtube.com/watch?v=tE4668aarck • Major Chemical Reactions: • http://www.youtube.com/watch?v=i-HHvx1VC_8 • An overly dramatized look at chemical reactions, via Hollywood: • http://www.youtube.com/watch?v=XS6JTr-mTWY
2-5 Organic and Inorganic Compounds • Nutrients • Essential molecules obtained from food • Metabolites • Molecules made or broken down in the body • InorganicCompounds • Molecules not based on carbon and hydrogen • Carbon dioxide, oxygen, water, and inorganic acids, bases, and salts • OrganicCompounds • Molecules based on carbon and hydrogen • Carbohydrates, proteins, lipids, and nucleic acids
2-6 Properties of Water • Water • Accounts for up to two-thirds of your total body weight • A solution is a uniform mixture of two or more substances • It consists of a solvent, or medium, in which atoms, ions, or molecules of another substance, called a solute, are individually dispersed
2-6 Properties of Water • Solubility • Water’s ability to dissolve a solute in a solvent to make a solution • Reactivity • Most body chemistry occurs in water • High Heat Capacity • Water’s ability to absorb and retain heat • Lubrication • To moisten and reduce friction
2-6 Properties of Water • The Properties of Aqueous Solutions • Ions and polar compounds undergo ionization, or dissociationin water • Polar water molecules form hydration spheres around ions and small polar molecules to keep them in solution
Figure 2-9 The Activities of Water Molecules in Aqueous Solutions Glucosemolecule Hydrationspheres Negativepole Cl H Positivepole Na
Figure 2-9a The Activities of Water Molecules in Aqueous Solutions Negativepole H Positivepole Water molecule. In awater molecule, oxygenforms polar covalentbonds with twohydrogen atoms.Because both hydrogenatoms are at one end ofthe molecule, it has anuneven distribution ofcharges, creating positive and negativepoles.
Figure 2-9b The Activities of Water Molecules in Aqueous Solutions Hydrationspheres Cl Na Sodium chloride insolution. Ionic compounds,such as sodium chloride,dissociate in water as thepolar water molecules breakthe ionic bonds in the largecrystal structure. Each ion insolution is surrounded bywater molecules, creatinghydration spheres.
Figure 2-9c The Activities of Water Molecules in Aqueous Solutions Glucosemolecule Glucose in solution.Hydration spheres alsoform around an organicmolecule containingpolar covalent bonds. Ifthe molecule bindswater strongly, as doesglucose, it will becarried into solution—inother words, it will dissolve. Note that themolecule does notdissociate, as occurs for ionic compounds.
2-6 Properties of Water • The Properties of Aqueous Solutions • Electrolytes and body fluids • Electrolytes are inorganic ions that conduct electricity in solution • Electrolyte imbalance seriously disturbs vital body functions
2-6 Properties of Water • The Properties of Aqueous Solutions • Hydrophilic and hydrophobic compounds • Hydrophilic • hydro- = water, philos = loving • Interacts with water • Includes ions and polar molecules • Hydrophobic • phobos = fear • Does NOT interact with water • Includes nonpolar molecules, fats, and oils
2-6 Properties of Water • Colloids and Suspensions • Colloid • A solution of very large organic molecules • For example, blood plasma • Suspension • A solution in which particles settle (sediment) • For example, whole blood • Concentration • The amount of solute in a solvent (mol/L, mg/mL)