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Chapter 2 The Chemical Level of Organization Lecture slides prepared by Curtis DeFriez, Weber State University Introduction • Since chemicals compose your body (and all body activities are chemical in nature), it is important to become familiar with the language and fundamental concepts of chemistry. How Matter is Organized • All forms of matter are composed of chemical elements which are substances that cannot be split into simpler substances by ordinary chemical means. – Elements are given letter abbreviations called chemical symbols. – Trace elements are elements in our bodies, present in tiny amounts . Structure of Atoms • Units of matter of all chemical elements are called atoms. An element is a quantity of matter composed of atoms of the same type. Atoms contain: Nucleus: protons (p+) & neutrons (no) Electrons (e-) surround the nucleus as a cloud Structure of Atoms • Electrons are very small and light (mass about 1/2000th that of proton or neutron), often represented as a “planet” orbiting the “sun” (atomic nucleus). In reality, they are found in a “cloud” of probability. This concept, however, made even Einstein’s head hurt – we can use the planets-orbiting-thesun model for this course! Structure of Atoms • Protons and neutrons form the nucleus of an atom; electrons surround the nucleus. • Protons are large, positively-charged particles – The number of protons in the nucleus (called the atomic number) determines the element (gold vs. silver vs. lead). Structure of Atoms • Neutrons are the second large particle that make-up the nucleus of atoms. – Unlike protons, neutrons have no charge. – They do add mass, however, and determine the variety, or “isotope” of a certain element, i.e. carbon-12 vs. carbon-14, which has 2 extra neutrons in nucleus Structure of Atoms • Mass is measured as a dalton (atomic mass unit). – Masses of subatomic particles • Neutron - mass of 1.008 daltons • Proton - mass of 1.007 daltons • Electron has mass of 0.0005 dalton Structure of Atoms • Certain numbers are used to describe different properties of atoms (of elements). – Atomic number is the number of protons in an atom. – Mass number is the sum of protons and neutrons in an atom and indicates how much the atoms “weighs”—this is always a whole number. – Atomic mass (atomic weight) is the average mass of all naturally occurring isotopes—since this is an average, it is not exactly a whole number. Structure of Atoms • The “numbers” of some of the more important elements for the human body are depicted in this graphic: Ions, Molecules, & Compounds • Ions are atoms that have given up or gained an electron in their outer electron shell (also called the valence shell). – Written with its chemical symbol and (+) or (–) Ions, Molecules, & Compounds • Molecules are formed when atoms share electrons. – Written as a molecular formula showing the number of atoms of each element (H2O) – The oxygen gas in the atmosphere we breath is really not oxygen the atom, but a pair of oxygen atoms linked together into an oxygen molecule (O2) . Ions, Molecules, & Compounds • A free radical is an electrically charged atom or group of atoms with an unpaired electron in its outermost shell. • They are unstable and highly reactive. – They can become stable by giving up an electron or taking an electron from another molecule . • Antioxidants are substances that inactivate oxygenderived free radicals. Chemical Bonds • The atoms of a molecule are held together by forces of attraction called chemical bonds. • The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost or valence shell. Atomic Structure and Bonds Interactions Animation • Atomic Structure and the Basis of Bonds You must be connected to the internet to run this animation. Chemical Bonds • Ionic bonds form when an atom loses or gains a valence electron. Ions are formed. – Positively and negatively charged ions are attracted to one another. – Cations are positively charged ions that have given up one or more electrons (they are electron donors.) – Anions are negatively charged ions that have picked up one or more electrons that another atom has lost (they are electron acceptors). Chemical Bonds Ionic Bond Formation Chemical Bonds • Covalent bonds are formed by the atoms of molecules sharing one, two, or three pairs of their valence electrons. – Covalent bonds are the strongest chemical bonds. – Single, double, or triple covalent bonds are formed by sharing one, two, or three pairs of electrons, respectively. Chemical Bonds • Covalent bonds may be nonpolar or polar. – In a nonpolar covalent bond, atoms share the electrons equally; nonpolar covalent bonds are the most common types of covalent bonds, as shown in this graphic depicting hydrogen gas, oxygen gas, nitrogen gas, and methane gas: Chemical Bonds • Polar covalent bonds are formed by the unequal sharing of electrons between atoms. • Polar covalent bonds are extremely important because the all-important water molecule makes use of this bond. • In water, oxygen attracts the hydrogen electrons more strongly, making oxygen slightly electronegative as indicated by the negative Greek delta sign. Chemical Bonds • Hydrogen bonds are weak interactions (approximately 5% as strong as covalent bonds) between hydrogen and adjacent electronegative atoms like oxygen or sulfur. – Hydrogen bonds result from attraction of oppositely charged parts of molecules—they should not be confused with covalent bonding to hydrogen which Chemical Bonds • Hydrogen bonds are useful in establishing links between molecules or between distant parts of a very large molecule. Large 3-D molecules (like proteins) are often held together by a great many hydrogen bonds. In water, hydrogen bonding provides considerable cohesion which creates a very high surface tension (as this bug demonstrates). Chemical Bonds Interactions Animation • Chemical Bonding You must be connected to the internet to run this animation. Chemical Reactions • Chemical reactions occur when electrons in the valence shell are shared or transferred. New bonds form and/or old bonds are broken. • Metabolism is the “sum of all the chemical reactions in the body”. • Law of conservation of energy: – The total mass of reactants equals the total mass of the products . Chemical Reactions • Energy (the capacity to do work) is transferred in a chemical reaction. • Kinetic energy is the energy of matter in motion. • Potential energy is energy stored by matter due to an object’s position in space, or stored in chemical bonds. Chemical Reactions • An exergonic reaction releases energy (usually in the form of heat during catabolism of food) by breaking a bond with more energy than the one being formed. • An endergonic reaction requires that energy be added, usually from a molecule called ATP, to form a bond. Chemical Reactions • Activation Energy is the energy required to break chemical bonds in the reactant molecules so a reaction can start. Chemical Reactions • Factors that cause a collision (and a chemical reaction to take place) include the temperature and the concentration of the reactants, and the presence or absence of a catalyst. • Catalysts are chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur. – Catalysts are neither consumed nor produced in the reaction. They are used over-and-over again, often several million times per second! Chemical Reactions • In a chemical reaction, a catalyst helps to properly orient the colliding particles of matter so that a reaction can occur at a lower collision speed. A catalyst does not alter the difference in potential energy between the reactants and products (it only lowers the amount of energy needed to get the reaction started.) Chemical Reactions • Types of chemical reactions can be broadly classified as: – Synthesis reactions – Anabolism • A + B ➙ AB – Decomposition reactions – Catabolism • AB ➙ A + B – Exchange reactions • AB + CD ➙ AD + CB – Reversible reactions • AC ↔ A + C Types of Reactions Interactions Animation • Types of Reactions and Equilibrium You must be connected to the internet to run this animation. Chemical Reactions • Types of Reactions and Equilibrium Interactions Animation You must be connected to the internet to run this animation. Inorganic & Organic Compounds Inorganic compounds are structurally simple molecules that usually lack carbon - like the salt potassium chloride (KCl) depicted here: • Organic compounds always contain carbon and are usually large, complex molecules. – Usually contain hydrogen – Always have covalent bonds Inorganic Compounds • Water is the most important and abundant inorganic compound in all living systems. • Water’s most important property is polarity, the uneven sharing of valence electrons that enables reactants to collide to form products. Inorganic Compounds Sodium and Chloride ions dissolve in the polar water molecules. Water Interactions Animation • Polarity and Solubility of Molecules You must be connected to the internet to run this animation Water and Fluid Flow Interactions Animation • Water and Fluid Flow You must be connected to the internet to run this animation. , Inorganic Compounds • Water as a solvent: – In a solution, the solvent dissolves the solute. – Substances which contain polar covalent bonds and dissolve in water are hydrophilic, while substances which contain non-polar covalent bonds are hydrophobic. – The polarity of water and its bent shape allow it to interact with several neighboring ions or molecules. – Water’s role as a solvent makes it essential for health and survival. Inorganic Compounds • Water has a high heat capacity, meaning it can absorb or release a relatively large amount of heat with only a modest change in its own temperature. • This property is due to the large number of hydrogen ions in water. Heat of vaporization (amount of heat needed to change from a liquid to a gas) is also high. – Evaporation of water from the skin removes large amounts of heat. Three Common Mixtures • A mixture is a combination of elements or compounds that are physically blended together but are not bound by chemical bonds. • In a solution, a substance called the solvent dissolves another substance called the solute. Usually there is more solvent than solute in a solution. – In our bodies, the most common solvent is water: We are 65-80% water (depending on age - babies are very “wet”… as anyone who has had one can attest.)