Phones must be put away now, no earbuds , no texting

1. Phones must be put away now, no earbuds, no texting • Do you have anything to turn in to green basket?

2. Chapter 2: Chemical Context of Life Atoms and Molecules

3. Elements and Compounds Organisms are composed of matter, whichis anything that takes up space and hasmass Matter is made up of elements, substancesthat cannot be broken down to other substances by chemical reactions 92 unique elements exist in nature • More have been created in the lab

4. + Sodium Chloride Sodium Chloride 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

5. Essential Elements of Life Essential elements • Include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. • Make up 96% of living matter

6. Other Elements A few other elements make up the remaining 4% of living matter

7. 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

8. 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

9. Subatomic Particles Protons and neutrons Are found in the atomic nucleus Electrons Surround the nucleus in a “cloud”

10. Cloud of negative charge (2 electrons) Electrons Nucleus (a) (b) 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. In this even more simplified model, the electrons are shown as two small blue spheres on a circle around the nucleus. Model of the Atom • Simplified models of an atom

11. 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 numberof 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

12. 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

13. Cancerous throat tissue Radioactive Isotopes Can be used in biology and medicine

14. 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

15. (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. Energy Levels The electrons of an atom • Differ in the amounts of potential energy they possess

16. 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. Electron Shells Energy levels • Are represented by electron shells

17. Electron Configuration and Chemical Properties Valence electrons • Are those in the outermost, or valence shell • Determines the chemical behavior of an atom The valence numberof an atom is the number of unpaired electrons in its valence shell This valence number determines the number of bonds the atom can form.

18. Helium 2He Atomic number 2 He 4.00 Hydrogen 1H Element symbol Atomic mass First shell Electron-shell diagram Beryllium 4Be Carbon 6C Oxygen 8O Neon 10Ne Lithium 3Li Boron 3B Nitrogen 7N Fluorine 9F Second shell Aluminum 13Al Chlorine 17Cl Argon 18Ar Sulfur 16S Sodium 11Na Magnesium 12Mg Silicon 14Si Phosphorus 15P Third shell Periodic Table (Campbell & Reece, p.32) The periodic table of the elements • Shows the electron distribution for all the elements

19. Which drawing depicts an atom with a valence of 2? A B C D E 0

20. Orbitals An orbital • Is the three-dimensional space where an electron is found 90% of the time

21. Electron orbitals. Each orbital holds up to two electrons. x Y 1s orbital 2s orbital Three 2p orbitals 1s, 2s, and 2p orbitals Z Electron-shell diagrams. Each shell is shown with its maximum number of electrons, grouped in pairs. (b) Second shell (maximum 8 electrons) (a) First shell (maximum 2 electrons) (c) Neon, with two filled shells (10 electrons) Orbitals Each electron shell • Consists of a specific number of orbitals

22. 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

23. Structure of an Atom http://www.wisc-online.com/objects/index_tj.asp?objid=GCH904

24. Bonds • The formation and function of molecules depend on chemical bonding between atoms.

25. 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

26. Hydrogen atoms (2 H) In each hydrogen atom, the single electron is held in its orbital by its attraction to the proton in the nucleus. + + 1 2 3 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. + + Hydrogen molecule (H2) Covalent Bonds Formation of a covalent bond

27. 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

28. Name (molecular formula) Electron- shell diagram Space- filling model Structural formula Hydrogen (H2). Two hydrogen atoms can form a single bond. H H Oxygen (O2). Two oxygen atoms share two pairs of electrons to form a double bond. O O Covalent Bonds • Single and double covalent bonds (a) (b)

29. Name (molecular formula) Electron- shell diagram Space- filling model Structural formula (c) Water (H2O). Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. H O H (d) Methane (CH4). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. H H H C H Covalent Bonds • Covalent bonding in molecules

30. 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

31. 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?

32. 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 H H d+ d+ H2O Polar Covalent Bonds In a polar covalent bond • The atoms have differing electronegativities • Share the electrons unequally

33. Water Models 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 H H d+ d+ H2O • Make 10 or more paper cut-outs of water atoms • Arrange them to demonstrate water crystal lattice

34. Covalent Bonds Reviewed

35. 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-

36. Ionic Bonds An anion • Atom that gains electrons • Is negatively charged • Cl-, PO43- A cation • Atom that lost electrons • Is positively charged • Na+, K+

37. The lone valence electron of a sodium atom is transferred to join the 7 valence electrons of a chlorine atom. Each resulting ion has a completed valence shell. An ionic bond can form between the oppositely charged ions. – + 1 2 Cl Na Na Cl Cl– Chloride ion (an anion) Na+ Sodium on (a cation) Na Sodium atom (an uncharged atom) Cl Chlorine atom (an uncharged atom) Sodium chloride (NaCl) Ionic Bonds An ionic bond • Is an attraction between anions and cations

38. Na+ Cl– Ionic Bonds Ionic compounds • Are often called salts, which may form crystals

39.  –  + A hydrogen bond results from the attraction between the partial positive charge on the hydrogen atom of water and the partial negative charge on the nitrogen atom of ammonia. H Water (H2O) O H  +  – Ammonia (NH3) N H H d+ + H Hydrogen Bonds A hydrogen bond • Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom  +

40. 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

41. Hybrid-orbital model (with ball-and-stick model superimposed) Ball-and-stick model Space-filling model Unbonded Electron pair O O H H H H 104.5° Water (H2O) H H C C H H H H H H Methane (CH4) Molecular Shape

42. Chemical Reactions Chemical reactions • Are the making and breaking of chemical bonds • Lead to changes in the composition of matter

43. + 2 H2 + O2 2H2O Reactants Reaction Product Chemical Reactions • Chemical reactions • Convert reactants to products

44. Equilibrium Chemical equilibrium • Is reached when the forward and reverse reaction rates are equal

45. 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