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Science, Systems, Matter, and Energy G. Tyler Miller’s Living in the Environment 13th Edition Chapter 3 Key Concepts Science as a process for understanding Components and regulation of systems Matter: forms, quality, and how it changes; laws of matter Energy: forms, quality, and how it changes; laws of energy Nuclear changes and radioactivity Frontier Science vs Consensus Science • News reports focus on: – New so-called scientific breakthroughs – Disputes between scientists over the validity of untested data • These preliminary results are called frontier science. They are controversial because they haven’t been tested or accepted. Remember, it’s healthy for scientists to disagree • Consensus science consists of data, theories, and laws that scientists who are considered to be experts in the field involved widely accept • This aspect of science is very reliable, but not considered to be newsworthy Models and Behavior of Systems A system is a set of components that: 1) function and interact in some regular and predictable manner, 2) can be isolated for the purposes of study A system has the following components: Inputs- things that flow into the system such as energy or matter Flows (throughputs)-matter or energy within the system at certain rates Stores (storage areas)- where matter or energy can accumulate before being released Outputs- matter or energy that flows out of a system and sinks into the environment System Regulation (Feedback Loops) Positive Feedback Homeostasis Negative Feedback Time Delay Synergy Fig. 3-3 p. 46 Matter: Forms, Structure, and Quality Elements Compounds Molecules Mixtures Elements • Elements are substances that cannot be broken down into simpler substances by ordinary chemical reactions – chemical symbols: usually the first or first and second letter of the English or Latin name • oxygen- O • sodium- Na • 92 naturally occurring elements ranging from hydrogen to uranium • Four elements (C, H, O, N) are responsible for over 96% of the mass of most organisms • Trace elements are those that are present, but in small amounts; equally necessary for organisms to function – e.g. iodine and copper Atoms • Atoms are the fundamental particles of elements • In order to be seen with the visible eye, the most advanced microscopes are magnified as high as 5 million times • Smallest component of an element that retains the chemical properties of an element – protons: carry a unit of positive charge – electrons: carry a unit of negative charge – neutron: uncharged particle • An electrically neutral atom contains the same number of electrons and protons • Protons and neutrons cluster together to form the atomic nucleus while electrons occupy empty spaces surrounding the nucleus • How do we identify atoms? – An atom in uniquely identified by its number of protons, the atomic number • The periodic table depicts the elements in order of their atomic number • The atomic number determines an atom’s identity and defines the element • Atomic numbers are denoted in subscript to the left of the chemical symbol 1 H = 1 proton 26 Fe = 26 protons • The mass of an atom is very small and cannot be expressed in grams or micrograms • Such masses are expressed in terms of the atomic mass unit (amu) o • The mass of an atom is referred to atomic mass and is indicated by the number of protons added to the number of neutrons • The atomic mass indicates approximately how much matter it contains as compared with another atom • Atomic mass number is denoted by a superscript to the left of the chemical symbol atomic mass 16 8 atomic number o Electron Orbitals • Electrons move through regions 3-D space around the nucleus, called orbitals • Each orbital contains different energy levels – electrons most distant from the nucleus have more energy because less energy is required for attraction to a positive charge • Valence electrons are those that contain the most energy – occupy valence shells • Electrons can move between orbitals as long as certain energy requirements are met Isotopes • Most elements consist of a mixture of atoms with different numbers of neutrons, thus having different masses • Isotopes of the same element have the same number of protons and electrons; only the number of neutrons vary 12 14 – e.g. C and C 6 6 Chemical Bonds Chemical formulas Ionic bonds Covalent bonds Hydrogen bonds Chemical Reactions • Atoms of different elements combine to form chemical compounds – atoms must be in fixed ratio • H2O: 2 atoms hydrogen to 1 atom oxygen • Two or more atoms can become very strongly joined to form a molecule – molecules are created by covalent bonds only • O2 or N2 not NaCl Chemical Bonds • Forces of attraction that hold atoms of a compound together • Energy required to break chemical bonds is the bond energy • Three types of bonds differing by the mechanism in which they form and their relative bond strength: – covalent bonds – ionic bonds – hydrogen bonds Covalent Bonds • Covalent bonds share electrons in such a way that each atom has a full valence shell – refer specifically to bonding of non-metals • Atoms tend to be reactive if the valence shell is not full • Lewis structures are simple ways of representing the electrons in the valence shell of an atom and how they are shared e.g. methane, CH4 carbon has 4 valence electrons all available for covalent bonding C hydrogen has 1 valence electron available for covalent bonding H H H H methane, CH4 H C methane, CH4 H H C methane, CH4 H H C H methane, CH4 H H C H H Special Covalent Bonds • Atoms of different elements vary in their affinity for electrons • Electronegativity is the measure of an atom’s attraction for electrons that are shared • When covalently bonded atoms have similar electronegativities, the electrons are shared equally. This state is described as nonpolar • If the electronegativities are different, the electrons are pulled closer to the atom with the greater electron affinity. This results in a polar covalent bond – has 2 dissimilar ends, or poles, one partially positive and one partially negative Ionic Bonds • Some atoms are not electrically neutral and will have more or less charge than another • A particle with one or more units of electrical charge is an ion which is formed by the addition or loss of 1 or more electrons – cations: a positively charged atom that has lost 1 or more electron from it’s valence shell – anions: a negatively charged atom that has gained 1 or more electron • Ionic bonds result from the attraction of a cation to an anion Ionic bonding Na has 1 valence electron and acts as a donor Cl has 7 valence electrons and acts as an acceptor • Compounds joined by ionic bonds tend to dissociate in water • Water acts as a solvent and dissovles many substances that are polar or ionic • NaCl, or any dissolved substance is referred to as a solute hydration Hydrogen Bonds • Hydrogen bonds are weak attractions involving partially charged hydrogen atoms • In a water molecule hydrogen is partially positively charged because the electron spends more time closer to the electronegative oxygen atom • Individually, hydrogen bonds are weak, but are collectively strong in large numbers – e.g. DNA Organic Compounds Organic vs. inorganic compounds: Organic compounds are those that contain carbon combined with another element Hydrocarbons- compounds of carbon and hydrogen, methane, for example Chlorinated hydrocarbons-compounds of carbon, hydrogen, and chlorine, DDT for example Organic Compounds Chlorofluorocarbons- compounds containing carbon, chlorine, and fluorine, Freon-12 for example Simple carbohydrates- certain compounds of carbon, hydrogen, and oxygen, glucose for example---C6H12O6 Complex carbohydrates- consist of two or more simple carbohydrates linked together Genetic Material Nucleic acids Genes Chromosomes Gene mutations Fig. 3-6 p. 50 The Four States of Matter Solid Liquid Gas Fig. 3-7 p. 50 Energy: Forms Kinetic energy Potential energy Heat Fig. 3-9 p. 52 The Law of Conservation of Matter Matter is not consumed Matter only changes form There is no “away” Matter and Pollution: How severe are pollutants? Chemical nature of pollutants Concentration Persistence Degradable (nonpersistent) pollutants: have broken down completely or reduced to acceptable levels Biodegradable pollutants- complex chemical pollutants that living organisms break down Slowly degradable (persistent) pollutants-take decades to degrade Nondegradable pollutants- cannot be broken down by natural processes Nuclear Changes: nuclei of isotopes change into a different isotope Natural radioactive decay Radioactive isotopes (radioisotopes) Gamma rays Alpha particles Beta particles Half life (See Table 3-2 p. 56) Fig. 3-13 p. 56 Ionizing radiation Nuclear Reactions Fission Fig. 3-16 p. 57 Fusion Fig. 3-17 p. 58 Effects of atomic bomb at Hiroshima Laws Governing Energy Changes First Law of Thermodynamics (Energy) Energy is neither created nor destroyed Energy only changes form You can’t get something for nothing ENERGY IN = ENERGY OUT Laws Governing Energy Changes Second Law of Thermodynamics In every transformation, some energy is converted to heat You cannot break even in terms of energy quality