The Internal Workings of Atoms and Molecules: A Insider's Perspective | CHEM 1010, Exams of Chemistry

Download The Internal Workings of Atoms and Molecules: A Insider's Perspective | CHEM 1010 and more Exams Chemistry in PDF only on Docsity! The Internal Workings of Atoms and Molecules: A Insider’s Perspective Ancient Greeks Answer - matter is composed of a limited number of basic, fundamental component substances called elements: What is matter composed of? CHEM 1010, Introductory Chemistry Chapter 3 Early alchemists demonstrated that the Greek’s concepts of four elements were incorrect & substances were composed of many more entirely different basic components. As alchemy evolved into the science of Chemistry it was first noted that certain pure substances could not be reduced to simpler substances by any chemical means. Element: A pure substance that cannot be broken down into simpler substances by chemical processes. Each of the 110+ known elements has its own distinctive name and symbol. Joseph Proust (1754 – 1826) Showed that a given compound always contained exactly the same proportion of elements by mass: Law of definite proportion Example: Ammonia NH3 %H Source 2 Source 1 %N Mass H (g) Mass N (g) Mass Sample (g) 25.89 16.69 21.28 13.72 4.61 2.97 82.2 82.2 17.8 17.8 14 g Nitrogen : 3 g Hydrogen John Dalton (1766 – 1844) After considerable experimentation into the manner in which the chemical composition changes in a definite way during chemical reactions, Dalton proposed a theory (a set of hypotheses) involving the concept of indestructible atoms. Dalton's Atomic Theory has 5 postulates Matter consists of definite, indivisible particles called atoms. Atoms are indestructible. Atoms of one particular element are identical in size, mass, and chemical properties. Atoms of different elements have different masses. Compounds are formed by binding together atoms of different elements in specific and definite ratios. Why do atoms of different elements have different masses? Dalton's atomic theory provided a convincing explanation for the composition of compounds. However, the general conception of an atom as a simple hard sphere of matter like a ball bearing or billiard ball did not explain why the masses of the atoms of the different elements were different. What is the structure of the atom? Gradually it was demonstrated through experiment that the atom was composed of even more basic constituents called sub-atomic particles. The Plum Pudding Model of the Atom. The atom was, on the whole, electrically neutral. Thus there must also be a source of positive charge within the atom, which exactly cancels out the negative charge of the electron. The “Plum Pudding Model” was proposed by another English chemist, William Thompson. − − − − − − − − − − − Spherical cloud of positive charge Electrons The Rutherford "Nuclear "Atom. In 1911, English Physicist Ernest Rutherford and co-workers carried out an experiment, which destroyed the "Plum Pudding" model and set the stage for the modern picture of the atom. While studying alpha particles (a form or radiation, positively charged particles with a mass 7,300× that of an electron), Rutherford found that these relatively massive particles could be deflected by collision with other equally massive particles. Shooting a beam of alpha-particles at a very thin gold foil, most of the alpha-particles passed through unaffected, but some had their path or trajectory greatly changed, some even being reflected backward! Most particles pass straight through foil Some α particles are scattered Source of α particles Screen to detect α particles Thin gold foil Beam of α particles The Neutron. The nucleus contains a third sub-atomic particle called the neutron. The neutron has approximately the same mass as the proton, but has no charge (it is neutral). The purpose of the neutron is unclear but it may help to hold the protons (which have a positive charge and will repel one another) together to form the nucleus Isotopes: Atoms of the same element (same number of protons in the nucleus), with different numbers of neutrons. 11 electrons 11 protons 12 neutrons 11 electrons 11 protons 13 neutrons Sodium Summary: Mass and Charge of the Electron, Proton & Neutron 01.675x10-241841Neutron +11.673x10-241836Proton -19.109x10-281Electron Relative ChargeMass, g Relative MassParticle nucleons Atomic Number: Mass Number: Number of protons in the nucleus of an atom Number of protons + number of neutrons of a particular isotope Z A Elements are designated by chemical symbols illustrating both the atomic number and the mass number. 6 —— Atomic number Cc Symbol of element (carbon) 12.01 Atomic weight (mass) Main groups Main groups ——i ———————— IA VILA () (18) 1 2 H IIA WIA IVA VA_ VIA VIIA He 1.0079 (2) (13) (14) (15) (16) (17) _4.00 3 4 5 6 7 8 9 10 Li | B iti B Cc N Oo F N 634 | 9.01 Transition metals 10.81 | 1201 | 14.01 | 16.00 | 19.00 | 20.18 11 12 ! 16 17 18 Na Mg / UIB IVB- VB_ VIB_ VIIB ———VIIB —— _ IB IIB Ss Cl Ar 22.99 | 24.31] (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) 32.06 35.45 39.95 19 20 21 22 23 24 25 26 27 ] 28 29 30 34 35 36 Ca Sc i Cr | Mn | Fe Co Ni Cu | Zn Se Br 39.10 | 40.08 | 44.96 | 47.87 | 50.94 | 52.00 | 54.94 | 55.84 | 58.93 | 58.69 | 63.55 | 65.41 78.96 79.90 $3.80 37 38 39 40 41 42 43 44 45 | 46 47 48 52 53 54 Rb Sr ys Zr Nb | Mo | Te | Ru Rh | Pd | Ag | Cd In Sn Sb I Xe 85.47 | 87.62 | 88.91 | 91.22 | 92.91 | 95.94 | 98 | 101.07] 102.90 | 106.42} 107.87 | 112.41 | 114.82 | 118.71 | 121.76 126.90 131.29 55 56 57 72 73 74 75 76 77 | 78 79 80 81 82 83 85 86 Cs | Ba | La |] Hf | Ta | W Re | Os Ir Pt | Au | Hg | Til | Pb} Bi At Rn 132.91 | 137.34 | 138.91 |] 178.49 | 180.95 | 183.84} 186.21 | 190.23} 192.22 | 195.08 | 196.97 | 200.59 | 204.38 | 207.19 | 208.98 210 222 87 88 89 104 | 105 | 106 | 107 | 108 109 | 110 | 111 | 112 | 113 | 114 | 115 | 116 | 117 | 118 Fr | Ra} Ac || Rf | Db Sg Bh | Hs | Mt | Ds 223 226 | 227 261 | 262 2 264 277 | 268 | 271 ss { 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 {| 68 | 69 { 70 { 71 Lanthanide series} Ce | Pr | Nd | Pm | Sm| Eu | Gd | Tb | Dy | Ho | Er | Tm} Yb] Lu 140.12 | 140.91 | 144.24 145 150.35 151.96 | 157.25 | 158.93 | 162.50} 164.93} 167.26 | 168.93 | 173.04 | 174.97 90 91 92 93 94 [ 95 96 97 98 99 | 100 | 101 | 102 | 103 Actinide sis Th | Pa U_| Np | Pu | Am} Cm} Bk | Cf | Es | Fm| Md} No} Lr 232.04 | 231.04 | 238.03 | 237 | 244 | 243 | 247 | 247 | 251 | 252 | 257 | 258 | 259 | 262 The mass of a hydrogen atom, 1H, is 1.674× 10−24 g, Since all of the mass is concentrated in the nucleus, the mass of a proton (1.673×10-24g) very closely approximates the mass of the 1H atom. Because of the very small values for the mass of atoms, grams are an inconvenient unit of measurement. The standard unit for measuring the mass of atoms is the atomic mass unit or amu. 1 amu ~ mass of proton = 1.661×10–24 g ! 92 238 U ! 39 89 Y Symbol # Protons # Neutrons # Electrons Net Charge 20 20 2+ 23 28 20 35 44 36 15 16 3− Natural carbon is a mixture of 12C, 13C, & 14C. 12C 98.89% 13C 1.11% Isotope Abundance 14C Negligible The mass of 12C is defined to be exactly 12 amu The mass of all other isotopes of carbon (and all other atoms) are measured relative to 12C. The Mass Spectrometer Measure the mass or other atoms relative to 12C using a mass spectrometer ionization Gas in Accelerate ions vacuum magnets Ion detector slit Some Features of the Periodic Table Elements having similar chemical properties lie in vertical columns called groups, labeled 1-18 Horizontal rows of the table are called periods, numbered from 1, beginning with the row that contains only H and He. Elements show gradual changes in chemical properties from left to the right: Periodic trend Compounds form by elements losing, gaining, or sharing electrons. Noble gases (Group 18) do not react to form any compounds. Thus, the number of electrons a noble gas has represents a stable number of electrons. He 2 4.00 Ne 10 20.18 Ar 18 39.95 Kr 36 83.80 Xe 54 131.3 Rn 86 222 18 To understand how and why compounds form, we must know something about the structure of the atom. If electrons are involved then where are they located in the atom? The energy of the electrons in each energy level or shell remains quantized. Thus, electrons can exist mainly in particular shells, but not with energies in between. Electrons are “held” in each energy level by their attraction to the nucleus. The closer the electrons are to the nucleus the more tightly they are held and the lower their energy is; they are less free to move about. Similar to the Bohr model, the smallest energy level or shell is the one closest to the nucleus (1st shell). Each subsequent energy level or shell is larger and exists further from the nucleus (numbered 2nd, 3rd,… etc.). The further the electron is from the nucleus (larger shells) the larger the energy of the electron; the electron is not held as tightly and is more free to move about. Again, noble gases are inert and do not react to form compounds. They do not want to gain, lose, or share electrons. The electron configuration of an atom is a statement of the number of electrons it has in each of its shells (and subshells). Each shell is broken into subshells. These subshells contain the various orbitals within which the electrons have the highest probability of being found. The subshells/orbitals are named: s, p, d, and f Within each shell is a set of orbitals, each one describing the region of space around the atom where an electron can be found with a 90% probability. The further the shell (and its orbitals) is from the nucleus, the greater its energy; similar to the Bohr model. Orbital Shapes “s” orbitals 1s 2s 3s 3s Shell number Type of orbital The number of electrons in any particular shell follow a 2n2 relationship in which n is the shell number. Shell 1 1s Shell 2 2s 2p Shell 3 3s 3p 3d Shell 4 4s 4p 4d 4f Shell 5 5s 5p 5d 5f 5g Shell 6 6s 6p 6d 6f 6g 6h Shell 7 7s 7p 7d 7f 7g 7h 7i X X X XXXXX X = 2 e- = 8 e- = 18 e- = 32 e- = 50 e- = 72 e- = 98 e- Helium + - - Helium is “happy” (stable) with two electrons in the 1st shell This configuration represents the maximum number of electrons that can occupy this small shell. Neon + - - 2e- 10e- The first shell can have 2e-, but no more; the shell is full or closed. The next shell available is the 2nd shell. The rest of the electrons go into this larger, higher energy shell. This is a stable configuration. - - - - - - -- Argon 18e- The first two shells are closed, once 10e- are placed in them. The next 8e- are then placed into the next highest energy shell, the 3rd shell.+- - - - - - - - -- - - - - - - - - This, again, represents a stable configuration, but with a partially filled shell. Krypton 36e- + - - - - - - - - -- - - - - - - - - -- - - - - - - - - - - - - - - - - The first three shells are filled to the max with 28 e-. The last 8 e- must go into the next higher energy shell; the 4th shell. This is another stable configuration with a partially filled shell. Atoms in the same group have the same number of valence electrons. Chemical properties are determined by the number of valence electrons an atom has. The period number is the same as the shell number where the valence electrons are located Transition metals 10 elements Inner transition metals 14 elements 1 2 3 4 5 6 7 n s f d p 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p Groups of columns tell us the particular subshell or orbital type that contains the valence electrons Chemical Bonding Allotropes of Carbon: Diamond Graphite Buckyballs Carbon nanotubes 10,000 times thinner than a human hair Similar in structure to buckyballs, but in tubular form Elements undergo chemical reactions that involve the loss, gain, or sharing of electrons that result from the tendency of a system to seek its lowest possible energy. Noble gas electron configuration - Lewis structures are a grouping of Lewis symbols that shows the transfer of electrons or the sharing of electrons in chemical bonds (compounds). Ionic bonds form from electrostatic attraction between oppositely charged ions that result from a complete transfer of electrons from one atom to another; from metal to nonmetal. Ionic Compounds A match made in “heaven”??? Metals like to lose electrons, nonmetals like to gain electrons We can predict the tendency of an element to form a cation or anion by noting its position in the periodic table. Metals easily give up e−, non-metals easily accept e−, each trying to gain an octet (noble gas e− configuration) Metals have a tendency to form cations +1 +2 +3 Group 1 metals: Group 2 metals: Group 13 metals (w|o B): Polyatomic ions: Hydronium ion - H3O+ Ammonium ion - NH4+ Carbonate ion - CO32- Bicarbonate ion - HCO3- Sulfate ion - SO42- Phosphate ion - PO43- Ionic compounds form a 3-D arrangement called a crystal lattice where the anions and cations occupy distinct sites within the lattice network: (+) = (−) The formula unit is the smallest whole number repeating ratio of ions that results in a neutral ionic compound. An ionic bond is the electrostatic attraction between oppositely charge ions. Ionic bonds are very strong…. High melting points (500° - 2000°C) (Conduct electricity in molten state) High boiling points Brittle Many ionic solids can dissolve into water to dissociate into ions. Insoluble ionic solids have ions that are too strongly attracted to each other for the energy of hydration to compensate. (b) Ba N (c) Ba SO4 (d) Ba OH 2 Sodium ion, Nat Chloride ion, Cl~ From Conceptual Chemistry, Second Edition by John Suchocki. Copyright © 2004 Benjamin Cummings, a division of Pearson Education. Minerals are inorganic ionic compounds. Many metals and nonmetals are necessary for our health, but not in the same amounts. The two separate atomic orbitals merge together as one with the greatest electron density (highest probability) between the nuclei. Cl + Cl → : : : . . : : : Octet Rule: In covalent bond formation, atoms go as far as possible toward completing their octets by sharing electron pairs. CH4 NH3 H2O C .. . . H . H.N :. . . H.O :. .. . Single bond: Double bond: Triple bond: Multiple covalent bonds C H 107 413 C O 143 358 C=O 123 745 C C 154 347 C=C 134 614 C≡C 120 839 C N 143 305 C=N 138 615 C≡N 116 891 N O 136 201 N=O 122 607 O H 96 467 Bond Length and Strength Bond type Length (pm) Bond Energy (kJ/mol) Bond type Length (pm) Bond Energy (kJ/mol) Diamonds Carbon atoms covalently bound together in a large highly-ordered network; essentially one gigantic molecule or macromolecule. C 90o Bond angle = 109.5o Consider the covalent compound H-F: FH M et al p la te M et al p la te +- F H δ-δ+ H-F is a polar covalent molecule in which the electrons in the bond are not shared equally. An atom’s ability to attract electrons in a bond is quantified by the atom’s electronegativity. Nonmetals have high electronegativity and metals have very low electronegativity Polar molecules with more than two atoms? A molecule can have a dipole (a positive side and a negative side) if there is an unequal distribution of electrons in the structure due to the presence of polar bonds. H2O Water has a bent structure that makes it polar. : : O H H If water did not have a bent structure, the polar bonds would essentially cancel each other out; like in a tug-of-war between two equally strong individuals. The electrons are pulled equally in opposite directions. Picture obtained from http://www.datasync.com/~rsf1/fun/bend-w.htm If water is polar it should be affected by an electric field. A nonpolar liquid would not be affected in the same way. 252 O22 10 Stoo Figure 3.15 Destruction by fire of the hydrogen-filled airship Hindenburg in New Jersey in 1937, after its inaugural transatlantic flight. (Archive Photo Royalty/ The Image Bank)