* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Ch. 2 Chemistry
Radical (chemistry) wikipedia , lookup
Biochemistry wikipedia , lookup
Computational chemistry wikipedia , lookup
Halogen bond wikipedia , lookup
Coordination complex wikipedia , lookup
Jahn–Teller effect wikipedia , lookup
Water splitting wikipedia , lookup
Artificial photosynthesis wikipedia , lookup
Oxidation state wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Livermorium wikipedia , lookup
Electrical resistivity and conductivity wikipedia , lookup
Photoelectric effect wikipedia , lookup
Electrochemistry wikipedia , lookup
Electrolysis of water wikipedia , lookup
Low-energy electron diffraction wikipedia , lookup
X-ray fluorescence wikipedia , lookup
Periodic table wikipedia , lookup
Metastable inner-shell molecular state wikipedia , lookup
Molecular orbital wikipedia , lookup
Hydrogen bond wikipedia , lookup
X-ray photoelectron spectroscopy wikipedia , lookup
History of chemistry wikipedia , lookup
Metalloprotein wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Chemistry: A Volatile History wikipedia , lookup
Molecular dynamics wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Bond valence method wikipedia , lookup
Bent's rule wikipedia , lookup
Extended periodic table wikipedia , lookup
Hydrogen atom wikipedia , lookup
Resonance (chemistry) wikipedia , lookup
IUPAC nomenclature of inorganic chemistry 2005 wikipedia , lookup
Atomic nucleus wikipedia , lookup
Electronegativity wikipedia , lookup
Atomic orbital wikipedia , lookup
Molecular orbital diagram wikipedia , lookup
Metallic bonding wikipedia , lookup
Hypervalent molecule wikipedia , lookup
History of molecular theory wikipedia , lookup
Electron configuration wikipedia , lookup
• Phones must be put away now, no earbuds, no texting • Do you have anything to turn in to green basket? Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 2: Chemical Context of Life Atoms and Molecules Elements and Compounds Organisms are composed of matter, which is anything that takes up space and has mass Matter is made up of elements, substances that cannot be broken down to other substances by chemical reactions 92 unique elements exist in nature • More have been created in the lab Compounds • A compound • Is a substance consisting of two or more elements combined in a fixed ratio • Has characteristics different from those of its elements + Sodium Chloride Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Sodium Chloride Essential Elements of Life Essential elements • Include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. • Make up 96% of living matter Other Elements A few other elements make up the remaining 4% of living matter Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Elements Each element Consists of a certain kind of atom that is different from those of other elements An atom Is the smallest unit of matter that still retains the properties of an element Subatomic Particles • Atoms of each element are composed of even smaller parts called subatomic particles • Relevant subatomic particles include • Neutrons, which have no electrical charge • Protons, which are positively charged • Electrons, which are negatively charged Subatomic Particles Protons and neutrons Are found in the atomic nucleus Electrons Surround the nucleus in a “cloud” Model of the Atom • Simplified models of an atom Cloud of negative charge (2 electrons) Electrons Nucleus (a) This model represents the electrons as a cloud of negative charge, as if we had taken many snapshots of the 2 electrons over time, with each dot representing an electron‘s position at one point in time. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings (b) In this even more simplified model, the electrons are shown as two small blue spheres on a circle around the nucleus. Atomic Number and Atomic Mass Atoms of the various elements • Differ in their number of subatomic particles The atomic number of an element • Is the number of protons • Is unique to each element The mass number of an element • Is the sum of protons plus neutrons in the nucleus of an atom • Is an approximation of the atomic mass of an atom Isotopes • Atoms of a given element may occur in different forms called Isotopes • Isotopes of a given element • Differ in the number of neutrons in the atomic nucleus • Have the same number of protons • Radioactive isotopes • Spontaneously give off particles and energy Radioactive Isotopes Can be used in biology and medicine Cancerous throat tissue Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Energy Levels of Electrons An atom’s electrons • Vary in the amount of energy they possess Energy • Is defined as the capacity to cause change Potential energy • Is the energy that matter possesses because of its location or structure Energy Levels The electrons of an atom • Differ in the amounts of potential energy they possess (a) A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons, because the ball can only rest on each step, not between steps. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Electron Shells Energy levels • Are represented by electron shells Third energy level (shell) Second energy level (shell) Energy absorbed First energy level (shell) Energy lost Atomic nucleus (b) An electron can move from one level to another only if the energy it gains or loses is exactly equal to the difference in energy between the two levels. Arrows indicate some of the step-wise changes in potential energy that are possible. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Electron Configuration and Chemical Properties Valence electrons • Are those in the outermost, or valence shell • Determines the chemical behavior of an atom The valence number of an atom is the number of unpaired electrons in its valence shell This valence number determines the number of bonds the atom can form. Periodic Table (Campbell & Reece, p.32) The periodic table of the elements • Shows the electron distribution for all the elements Helium Hydrogen 1H Atomic mass First shell 2 He 4.00 Atomic number 2He Element symbol Electron-shell diagram Lithium 3Li Beryllium 4Be Boron 3B Carbon 6C Nitrogen 7N Silicon 14Si Phosphorus 15P Oxygen 8O Fluorine 9F Neon 10Ne Sulfur 16S Chlorine 17Cl Argon 18Ar Second shell Sodium Magnesium Aluminum 13Al 11Na 12Mg Third shell Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Which drawing depicts an atom with a valence of 2? a. A b. B c. C d. D e. E Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Orbitals An orbital • Is the three-dimensional space where an electron is found 90% of the time Orbitals Each electron shell • Consists of a specific number of orbitals Electron orbitals. Each orbital holds up to two electrons. x Y Z 1s orbital 2s orbital Three 2p orbitals 1s, 2s, and 2p orbitals Electron-shell diagrams. Each shell is shown with its maximum number of electrons, grouped in pairs. (a) First shell (maximum 2 electrons) (b) Second shell (maximum 8 electrons) Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings (c) Neon, with two filled shells (10 electrons) Orbitals Filling pattern of electron orbitals: Electrons fill lower shells first before outer shells • First: two electrons in 1s orbital • Then: two electrons 2s orbital • Then: one electron in each of 2p orbitals before adding more to any 2p if necessary Carbon breaks these rules: sp3 hybridization • Allows 4 unpaired electrons = 4 bonds Structure of an Atom http://www.wisconline.com/objects/index_tj.asp?objid=G CH904 Bonds • The formation and function of molecules depend on chemical bonding between atoms. Bonds • The formation and function of molecules depend on chemical bonding between atoms. • A covalent bond • Is the sharing of a pair of valence electrons Covalent Bonds Formation of a covalent bond Hydrogen atoms (2 H) 1 2 3 In each hydrogen atom, the single electron is held in its orbital by its attraction to the proton in the nucleus. When two hydrogen atoms approach each other, the electron of each atom is also attracted to the proton in the other nucleus. The two electrons become shared in a covalent bond, forming an H2 molecule. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings + + + + + + Hydrogen molecule (H2) Covalent Bonds A molecule • Consists of two or more atoms held together by covalent bonds A single bond • Is the sharing of one pair of valence electrons A double bond • Is the sharing of two pairs of valence electrons Covalent Bonds • Single and double covalent bonds Name (molecular formula) Electronshell diagram (a) Hydrogen (H2). Two hydrogen atoms can form a single bond. (b) Oxygen (O2). Two oxygen atoms share two pairs of electrons to form a double bond. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Structural formula H H O O Spacefilling model Covalent Bonds • Covalent bonding in molecules Name (molecular formula) Electronshell diagram (c) Water (H2O). Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. (d) Methane (CH4). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. Structural formula O H H H H C H Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings H Spacefilling model Electronegativity Electronegativity • Is the attraction of a particular kind of atom for the electrons in a covalent bond The more electronegative an atom • The more strongly it pulls shared electrons toward itself In a nonpolar covalent bond • The atoms have similar electronegativities • Share the electron equally Thinking Question Electronegativity values increase as the atom becomes smaller and as you go from left to right on the Periodic Table. Why do you think this is so? Polar Covalent Bonds In a polar covalent bond • The atoms have differing electronegativities • Share the electrons unequally Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. d– This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. O d+ H H H2O Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings d+ Water Models •Make 10 or more paper cut-outs of water atoms •Arrange them to demonstrate water crystal lattice Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. d– This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. O d+ H H H2O Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings d+ Covalent Bonds Reviewed Ionic Bonds In some cases, atoms strip electrons away from their bonding partners Electron transfer between two atoms creates ions Ions • Are atoms with more or fewer electrons than usual (charged atoms) • Such as Na+, Cl-, K+, PO43- Ionic Bonds An anion • Atom that gains electrons • Is negatively charged • Cl-, PO43- A cation • Atom that lost electrons • Is positively charged • Na+, K+ Ionic Bonds An ionic bond • Is an attraction between anions and cations 1 The lone valence electron of a sodium 2 Each resulting ion has a completed atom is transferred to join the 7 valence electrons of a chlorine atom. valence shell. An ionic bond can form between the oppositely charged ions. – + Na Na Sodium atom (an uncharged atom) Cl Cl Chlorine atom (an uncharged atom) Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Cl Na Na+ Sodium on (a cation) Cl– Chloride ion (an anion) Sodium chloride (NaCl) Ionic Bonds Ionic compounds • Are often called salts, which may form crystals Na+ Cl– Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen Bonds A hydrogen bond • Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom d– Water (H2O) d+ O H d+ d– Ammonia (NH3) N H d+ H d+ Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings A hydrogen H bond results from the attraction between the partial positive charge on the hydrogen atom of water and the partial negative charge H d+ on the nitrogen atom of ammonia. Molecular Shape and Function The precise shape of a molecule • Is usually very important to its function in the living cell • Is determined by the positions of its atoms’ valence orbitals Molecular Shape Space-filling model Ball-and-stick model Hybrid-orbital model (with ball-and-stick model superimposed) Unbonded Electron pair O O H Water (H2O) 104.5° H H H H C C H H Methane (CH4) H H Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings H H H Chemical Reactions Chemical reactions • • Are the making and breaking of chemical bonds Lead to changes in the composition of matter Chemical Reactions • Chemical reactions • Convert reactants to products + 2 H2 + O2 Reactants Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings 2H2O Reaction Product Equilibrium Chemical equilibrium • Is reached when the forward and reverse reaction rates are equal Key Points of Chapter 2 • Matter consists of chemical elements in pure form and in combinations called compounds • An element’s properties depend on the structure of its atoms • The formation and function of molecules depends on chemical bonding between atoms • Chemical reactions make and break chemical bonds