CHEMISTRY: Unit One J. us?!

Transcription

1 CHEMISTRY: Unit One J : Q E How does knowledg e of the micro scopic ato m help us u nderstan d the chemical world aro und us?!

2 Conversational Question: 0 What do you think your desk is made of? 0 The nature of matter has evolved over time. (years ago people would have answered, Earth ) 0 Let s explore our chemical past to sort through this question

3 What is chemistry? 0 The study of MATTER à anything having mass and volume. 0 Chemistry describes the composition of matter and the various changes it undergoes.

4 SO what are we made of? 0 Dalton s Atomic Theory: 0 Elements are composed of ATOMS, or the basic unit of matter. 0 Other experiments theorized and/or concluded: 0 The atom contains small, negatively charged particles = electrons (J.J. Thomson via cathode ray tube), scattered throughout evenly. 0 Plum-pudding model

5 0 What else makes" up an atom? 0 Ernest Rutherford directed positively charged particles at thin piece of gold foil. 0 Some particles were deflected/bounced back. 0 CONCLUSION: atoms have a dense central core called a nucleus, & the rest is empty space. The Gold-Foil Experiment

6 What else makes up an atom? 0 At this point, what do we know? à Atoms have electrons (-) and a nucleus à Atoms are electrically neutral! 0 What s missing?? à POSTIVITY! à Positive charge à Neutral (no charge)

7 Bohr Model: 0 Planetary Model 0 center 0 Electrons orbit around nucleus in fixed manner 0 Valence Electrons: electrons in the outermost shell around a nucleus 0 First shell à Max. 2 valence electrons (K) 0 Second shell à Max. 8 valence electrons (L) 0 **Check out the PERIODIC TABLE

8 Bohr Model: 0 Practice Question: 0 What is Na s electron arrangement? 0 Answer:

9 Wave-Mechanical Model: s: energy and matter viewed as both waves and particles. 0 STILL (like Bohr) has dense positively charged nucleus, BUT electrons carry energy around in orbitals. 0 These orbitals are the regions where electron energy is likely to be located.

10 Checkpoint Assessment: 0 Match the pictures with the experiment or scientist responsible: 0 1) 0 4) 0 3) 02) 1) Bohr 2) Plum-Pudding (Thomson) 3) Dalton 4) Wave-Mechanical (modern) 5) Gold-Foil (Rutherford) 0 5)

11 THE ATOM 0 Subatomic Particles à RECAP! 0 Proton (+) & inside nucleus 0 Neutron (0) & inside nucleus 0 Electron (-) & outside nucleus in orbitals 0 SO, what s the overall charge of the NUCLEUS?? 0 Atoms are SUPER small so in order to figure out their mass we use units called atomic mass units (amu). It s the measure of atomic mass. 0 Each PROTON & NEUTRON have an atomic mass of 1.0. Electrons mass is so much smaller, its negligible and considered ZERO amu.

12 Inside the Nucleus 0 Let s take a the periodic table: 0 Element Li = Lithium is what #? 0 Atomic # à the # of protons of a given element 0 All atoms of a given element have the same # of protons in its nucleus.

13 Inside the Nucleus 0 Mass #: The number of protons + neutrons in the nucleus 0 Use the periodic table to determine the atomic # s and mass # s of the following elements. 1) C (carbon) 2) O (oxygen) 3) K (potassium) 4) Be (beryllium) à 6 & 12amu à 8 & 16amu à 19 & 39amu à 4 & 9amu

14 Practice PrObLeMs: 0 Find the # of neutrons in an atom of 79 Se 0 à atomic # = 34 à mass # = 79 0 so, # of neutrons = mass # - atomic #! 0 ANSWER: = 45 neutrons! 0 Find the # of neutrons in an atom of 23 Na 0 à atomic # = 11 à mass # = 23 0 so, # of neutrons = mass # - atomic #! 0 ANSWER: = 12 neutrons!" 0 But why is the mass on the periodic table not a whole number???

15 Inside the Nucleus 0 Let s look at Nitrogen Atomic # = 7 0 Atomic Mass = amu! Where did this # come from? 0 The # of neutrons can vary for the same element. 0 Atomic Mass: Average masses of all isotopes of an element 0 ISOTOPES: atoms of same elements having different mass numbers, or number of neutrons. 0 The # that FOLLOWS (proceeds) the isotopes name is that isotopes mass. 0 Ex) Carbon -14 => means 14 C, or this carbon s mass = 14amu

16 Average Atomic Mass: 0 Question: Why does Chlorine have an atomic mass of amu? 0 There are 2 major isotopes of Chlorine Cl-35 & Cl-37.!!!!! 0 The Atomic Mass is the average of the masses of the two isotopes.why isn t it 36 then?

17 Average Atomic Mass: 0 Sample Test Grades: Pretend you re not a student at TYWLS and are graded using a scale. The following are your test grades thus far: 0 90%, 80%, 90%, 90% 0 What is your current average?? = 350! 350 / 4 = 87.5 à Average! 0 Similarly, if there are more atoms of one isotope of Chlorine than the other, the average mass would be CLOSER to the isotope that s most abundant à let s check it out. 0 Just by looking at the periodic table, which Cl isotope would be most abundant?? **SHORTCUT**

18 Example:" à Nitrogen 0 Nitrogen s Atomic Mass? amu 0 Look at the TWO isotopes of Nitrogen above 0 14 N is 99.63% abundant & 15 N is 0.37% abundant 0 Calculate: the atomic mass of Nitrogen. 14 amu x = amu 15 amu x = amu à Add two amu products get answer (closest to periodic table average!)

19 Example:" à Rubidium 0 85 Rb is 72.2% abundant & 87 Rb is 27.8% abundant 0 Calculate: the atomic mass of Rubidium. 85 amu x = amu 87 amu x = amu à SO, what s our (average) atomic mass of Rubidum?? à = (rounded) *sig figs (we will discuss later)

20 OUTSIDE the nucleus 0 Electrons (we now know) are found in ORBITALS around the nucleus. 0 Electrons occupy ENERGY LEVELS, depending on the amount of energy they contain. 0 Electrons CAN MOVE from one energy level to another, but ONLY due to a discrete, fixed amount of ABSORBED energy. 0 Climbing up the stairs*can t stop half way up a stair! 0 In the same way, electrons must GIVE OFF or ABSORB the energy difference between any two given levels.

21 GROUND STATE 0 Electrons that occupy the LOWEST orbital are in the Ground State. 0 Ex) Na à how many electrons does it have? What s it s electron configuration? 0 11 organized as (check periodic table) 0 Climbing up the stairs*can t stop half way up a stair, can you?? 0 In the same way, electrons must GIVE OFF or ABSORB the energy difference between any two given levels.

22 EXCITED STATE How do you think an electron becomes excited? What happens to you when YOU become excited about/over something?? 0 Electrons must absorb energy to temporarily move to a higher energy level think caffeine ;) 0 Let s look again at Sodium: Ground state = Excited State example: How does it become excited though??

23 EXCITED STATE 0 Excited=ABSORBED energy 0 Stimuli such as heat, light, and/or electricity can be absorbed by electrons and make them jump to an excited state. 0 When go back to ground state, it must RELEASE/EMIT the same amount of energy it gained!!! 0 Example: NEON/Fluorescent Lights à they are excited electrons releasing energy in the form of light toward ground state

24 Spectroscopy & energy 0 The emission of light from electrons going to GROUND STATE can be seen because it exists at different wavelengths. 0 These emission lines can be viewed through a spectroscope, or an instrument which acts as a prism and bends the light rays of specific samples, called bright line spectra. 0 Atom s have their own distinct patterns of emission lines.

25 BrIgHt LiNe SpEcTrA.. What elements does this spectral sample contain in it??

26 Quantum Numbers! 0 Quantum Theory: Our way of understanding the chemical behavior or atoms (based on their electrons) 0 PRINCIPAL quantum # s: Same as their energy level.aka, energy level #1 = quantum #1, & so on 0 Say hi to your BFF now. J (no, not ME lol) 0 Each ROW (numbered) correlates to that energy level

27 Quantum Numbers! 0 Each energy level has one or more sublevels associated with it.s, p, d, &/or f 0 EACH orbital can have a max of 2 electrons (ONE PAIR). 0 S = 1 pair/orbital (2 electrons) 0 P = 3 pairs/orbitals (6 electrons) 0 D = 5 pairs/orbitals (10 electrons) 0 F = 7 pairs/orbitals (14 electrons)

28 Electron Configuration 0 RULES (how-to): Follow your periodic table blocks according to this diagram (they are segmented on the table for a reason!) **electrons want to be as stable as possible (aka GROUNDED) so they fill this pattern filling the LOWEST ENERGY LEVELS first *FOLLOW THE PERIODIC BRICK ROAD!*

29 Electron Configuration 0 BEYOND energy level 4: 0 Once you hit the Dblock, each energy level within which e - are located are n-1 0 Ex) Cu: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9 The d block drops one energy level à which explains why the third energy level has a max of 18 electrons on the periodic table configurations!

30 Electron Configuration Na: 1s 2 2s 2 2p 6 3s 1 Examples: Using Hund s Rule à unpaired electrons first (look below) Identify electrons with arrows as follows: Try: Phosphorus (P)

31 Electron Configuration 0 Calculating Valence Electrons: 0 Add up all the superscripts in the highest energy level present in the configuration 0 Ex) 1s 2 2s 2 2p 6 3s 2 3p 4 = how many? à 3s 2 3p 4 = highest energy level so add, 2+4 = 6 0 Ex) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7 0 What element? Valence electrons? 0 Cu & 2 (4 th energy level) à confirm on Periodic Table?* for these look at periodic table don t bother calculating! J J J J à easy squeezy lemon peezy!

32 Electron Configuration Excited v. Ground State 0 We evaluate this in the same way we did standard configuration, we just need to display it within the orbitals: 0 Ex)which electron configuration represents an atom in the excited state? 0 A) 1s 2 2s 2 2p 6 3s 2 0 B) 1s 2 2s 2 2p 6 3s 1 0 C) 1s 2 2s 2 2p 6 0 D) 1s 2 2s 2 2p 5 3s 1 0 CHOICE D

33 Electron Configuration Noble Gas Configuration: SHORTCUT! 0 Let s look at Fe (Iron): 0 The TOP = standard electron configuration! 0 The BOTTOM = Shortcut = using noble gases since their valence shells are completely full, it s understood that all electrons up to and including that element are accounted for then proceed as usual until element location has been met

34 Types of matter 0 Two MAJOR types: 1) Pure Substances 2) Mixtures"

35 Types of matter What s the difference?" 0 Pure Substances are composed of the same type of matter throughout the sample (homogeneous) or having uniform composition 0 Mixtures are combos of 2 or more pure substances that CAN BE separated by physical means (homogeneous &/or heterogeneous)à varying composition, not uniformly dispersed or mixed, different chemical & physical properties

36 Pure Substances 0 Elements: substances that CANNOT be broken down or decomposed into simpler substances by chemical means 0 Compounds: substances composed of 2 or more elements; chemically combined in definite proportions by mass; same composition throughout

37 Mixtures 0 Elements can be present in different ratios! 0 Each substance that composes the mixture RETAINS its properties