This document provides an overview of chemistry concepts including: 1) Matter is anything that occupies space and has mass, and can be classified as elements, compounds, or mixtures. 2) The periodic table organizes the known elements and provides information about their properties based on atomic structure. 3) Chemical and physical changes involve changes in the identities and bonding of atoms and molecules. Exo- and endothermic reactions involve the absorption or release of energy.

1. LECTURE 2- SCIENVC

2. Matter is anything that occupies space and has mass. A substance is a form of matter that has a definite composition and distinct properties. Chemistry is the study of matter and the changes it undergoes liquid nitrogen gold ingots silicon crystals

3. Classifying Matter All Matter Pure Substances Mixtures Can it be separated by a physical process? Compounds Elements YES NO Can it be broken down into simpler ones by chemical means ? NO YES

6. The Modern Periodic Table Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal

7. A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions. Compounds can only be separated into their pure components (elements) by chemical means. lithium fluoride quartz dry ice – carbon dioxide

9. Physical means can be used to separate a mixture into its pure components. magnet distillation

10. A Comparison: The Three States of Matter

11. A physical change does not alter the composition or identity of a substance. A chemical change alters the composition or identity of the substance(s) involved. Types of Changes ice melting sugar dissolving in water hydrogen burns in air to form water

12. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei Atomic number, Mass number and Isotopes X A Z H 1 1 H (D) 2 1 H (T) 3 1 U 235 92 U 238 92 Mass Number Atomic Number Element Symbol

13. Electron configuration is how the electrons are distributed among the various atomic orbitals in an atom. 1s 1 Orbital diagram H principal quantum number n angular momentum quantum number l number of electrons in the orbital or subshell 1s 1

14. What is the electron configuration of Mg? Mg 12 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s 2 2s 2 2p 6 3s 2 2 + 2 + 6 + 2 = 12 electrons Abbreviated as [Ne]3s 2 [Ne] 1s 2 2s 2 2p 6 What are the possible quantum numbers for the last (outermost) electron in Cl? Cl 17 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s 2 2s 2 2p 6 3s 2 3p 5 2 + 2 + 6 + 2 + 5 = 17 electrons Last electron added to 3p orbital n = 3 l = 1 m l = -1, 0, or +1 m s = ½ or -½

15. The Modern Periodic Table Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal

16. The electrons in the outermost energy levels are called valence electrons. The group number (of the representative elements) on the periodic table tells you the number of valence electrons. 1A 2A 3A 4A 5A 6A 7A 8A Group 1A: 1 valence electron Group 3A: 3 valence electrons

17. What is the electron configuration of C? C 6 electrons 1s < 2s < 2p 1s 2 2s 2 2p 2 2 + 2 = 4 valence electrons How many valence electrons are there in O? N? H? C O N H

18. A covalent bond is a chemical bond in which two or more electrons are shared by two atoms. Why should two atoms share electrons? Lewis structure of F 2 F F + 7e - 7e - F F 8e - 8e - F F F F lone pairs lone pairs lone pairs lone pairs single covalent bond single covalent bond

19. + + Lewis structure of water Double bond – two atoms share two pairs of electrons or Triple bond – two atoms share three pairs of electrons or 8e - H H O O H H O H H or 2e - 2e - single covalent bonds O C O O C O 8e - 8e - 8e - double bonds double bonds N N 8e - 8e - N N triple bond triple bond

21. Write the Lewis structure of nitrogen trifluoride (NF 3 ). Step 1 – N is less electronegative than F, put N in center Step 2 – Count valence electrons N - 5 (2s 2 2p 3 ) and F - 7 (2s 2 2p 5 ) 5 + (3 x 7) = 26 valence electrons Step 3 – Draw single bonds between N and F atoms and complete octets on N and F atoms. Step 4 - Check, are # of e - in structure equal to number of valence e - ? 3 single bonds (3x2) + 10 lone pairs (10x2) = 26 valence electrons F N F F

22. Lewis structure of neutral molecules 4 bonds 3 bonds 2 bonds 1 bond O N H C

23. 3 ways of representing the reaction of H 2 with O 2 to form H 2 O A process in which one or more substances is changed into one or more new substances is a chemical reaction A chemical equation uses chemical symbols to show what happens during a chemical reaction reactants products

24. How to “Read” Chemical Equations 2 Mg + O 2 2 MgO 2 atoms Mg + 1 molecule O 2 makes 2 formula units MgO 2 moles Mg + 1 mole O 2 makes 2 moles MgO 48.6 grams Mg + 32.0 grams O 2 makes 80.6 g MgO NOT 2 grams Mg + 1 gram O 2 makes 2 g MgO

29. C 18 H 36 O 2 + O 2 CO 2 + H 2 O

30. 3.60 Balance the following equations: a. N 2 O 5 -> N 2 O 4 + O 2 b. KNO 3 -> KNO 2 + O 2 c. NH 4 NO 3 -> N 2 O + H 2 O d. NH 4 NO 2 -> N 2 + H 2 O e. NaHCO 3 -> Na 2 CO 3 + H 2 O + CO 2 f. P 4 O 10 + H 2 O -> H 3 PO 4 g. HCl + CaCO 3 -> CaCl 2 + H 2 O + CO 2 h. Al + H 2 SO 4 -> Al 2 (SO 4 ) 3 + H 2 i. CO 2 + KOH -> K 2 CO 3 + H 2 O

31. 3.60 Balance the following equations (continuation): j. CH 4 + O 2 -> CO 2 + H 2 O k. Be 2 C + H 2 O -> Be(OH) 2 + CH 4 l. Cu + HNO 3 -> Cu(NO 3 ) 2 + NO + H 2 O m. S + HNO 3 -> H 2 SO 4 + NO 2 + H 2 O n. NH 3 + CuO -> Cu + N 2 + H 2 O

33. How do we relate balanced chemical reactions to energy?

35. Heat is the transfer of thermal energy between two bodies that are at different temperatures. Energy Changes in Chemical Reactions Temperature is a measure of the thermal energy . Temperature = Thermal Energy

36. Exothermic process is any process that gives off heat – transfers thermal energy from the system to the surroundings. Endothermic process is any process in which heat has to be supplied to the system from the surroundings. 2H 2 ( g ) + O 2 ( g ) 2H 2 O ( l ) + energy H 2 O ( g ) H 2 O ( l ) + energy energy + 2HgO ( s ) 2Hg ( l ) + O 2 ( g ) energy + H 2 O ( s ) H 2 O ( l )

37. Schematic of Exothermic and Endothermic Processes

38. First law of thermodynamics – energy can be converted from one form to another, but cannot be created or destroyed.  E system +  E surroundings = 0 or  E system = -  E surroundings Exothermic chemical reaction! C 3 H 8 + 5O 2 3CO 2 + 4H 2 O Chemical energy lost by combustion = Energy gained by the surroundings system surroundings

39. Enthalpy (H) is used to quantify the heat flow into or out of a system in a process that occurs at constant pressure.  H = H (products) – H (reactants)  H = heat given off or absorbed during a reaction at constant pressure H products < H reactants  H < 0 H products > H reactants  H > 0

40. Thermochemical Equations Is  H negative or positive? System absorbs heat Endothermic  H > 0 6.01 kJ are absorbed for every 1 mole of ice that melts at 0 0 C and 1 atm. H 2 O ( s ) H 2 O ( l )  H = 6.01 kJ/mol

41. Thermochemical Equations Is  H negative or positive? System gives off heat Exothermic  H < 0 890.4 kJ are released for every 1 mole of methane that is combusted at 25 0 C and 1 atm. CH 4 ( g ) + 2O 2 ( g) CO 2 ( g) + 2H 2 O ( l )  H = -890.4 kJ/mol

44. Entropy (S) is a measure of the randomness or disorder of a system. order S disorder S

45. Processes that lead to an increase in entropy (  S > 0)

46. Chemistry In Action: The Efficiency of Heat Engines Some of the work is wasted as heat !!! Efficiency = X 100% T h - T c T h

47. Different forms of energy are converted to heat. Heat are dispersed in the surroundings. Increases the entropy of the universe. “ Chaotic” World???

48. Can you imagine how life would be If there were no entropy? Or, making matters even worse, The law of entropy were reversed? Books would get straighter on their shelves, And children's rooms would clean themselves! And every rock or stick or tree Would form a crystal, perfectly. There'd be no anarchy or war For everyone would know the score. Every thing and every face Would have its certain time and place. Replacing every beach would pass An endless stretch of flawless glass. The sea would be the brightest blue, And every day the sky would too. How beautiful would be our world If order did command it. If all were straight and never curled: Perhaps we should demand it. You'd think a world sans entropy Would be a lovely place to be. I said this recently myself, As all my books fell off their shelf. Yet pondering this ordered bliss, I noticed things that I would miss, Like rolling waves upon the sea, Or sugar for my morning tea: The sugar won't dissolve, it's true, That ant-entropy holds like glue. And after that, I saw with grief, There'd be no fractaled maple leaf: No beauty in the summer wood, Should chaos disappear for good. What a bore, to know each day Would turn out in the same old way. If entropy would disappear There'd be no fortune, fate or luck And even after many years, Vegas wouldn't make a buck. Chaos, Keep It Coming! By Heather Ryphemi Stregay