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Chemistry 115 Note outlines Historical development of the nature of matter Democritus (~460-370 BC) ♦ Known by peers as the ‘laughing philosopher,’ because he emphasized the value of ‘cheerfulness’ ♦ Elaborated the “atomist theory” originated by his teacher, Leucippus − Democritus proposed that atomos..... − were small hard particles − were made of a single material − were always moving − formed different materials by joining together ♦ Apocryphal legend of theory inspiration: Horses on a distant hill − Indisputably individual entities-yet they looked like one continuous mass − Thought experiment: Maybe if had we had better eyes we could see these atomos ♦ He was ridiculed by scientists of his day ♦ His theory largely forgotten for 2000 years Aristotle (~384-322 BC) ♦ Proponent of continuous theory of matter ♦ Largely responsible from dismissal of Democritus’ theory John Dalton (~1805) ♦ British school teacher and chemist ♦ Performed experiments to determine how elements join together to form new substances ♦ Recognized his results were inconsistent with existing theory ♦ ♦ ♦ “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 1 of 10 Chemistry 115 Note outlines Dalton’s Atomic Theory Dalton postulated that: 1. All matter consists of atoms; tiny indivisible particles of an element that cannot be created or destroyed. 2. Atoms of one element cannot be converted into atoms of another element. 3. Atoms of an element are identical in mass and other properties to all other atoms of the same element and are different from the atoms of any other element. 4. Compounds result from the chemical combination of a specific ratio of atoms of different elements. The law of mass conservation ♦ Arisotle’s and Dalton’s theories were both consistent with the Law of Mass Conservation Law of Definite (or Constant) Composition ♦ No matter the source, a particular compound is composed of the same elements in the same parts (fractions) by mass Purified calcium carbonate obtained from grinding up coral from the south Mediterranean sea Purified calcium carbonate obtained from limestone dug up in Preston county, WV − − − − − − “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 2 of 10 Chemistry 115 Note outlines Law of Multiple Proportions ♦ A pure compound always contains the same elements in the same proportions by mass ♦ If particles were infinitely divisible we would see an infinite number of mass ratios. Again, we do not! Dalton’s interpretation: If there are two elements that can combine(for example carbon and oxygen), their combinations will occur in a set sequence. − The first compound will have one atom of carbon and one of oxygen − Another, one atom of carbon and two atoms of oxygen − And so on A theory must be discarded or refined when it can't explain new experimental results ♦ Continuous matter; the idea that matter is infinitely divisible could account for the BUT...... ♦ It is inconsistent with the Law of Definite (or Constant) Composition and the Law of Multiple Proportions ♦ So we must conclude that the continuous theory of matter is invalid so must be discarded Concept Check A long standing and time tested, consistent explanation of known observations is called a. an experiment b. a hypothesis c. a prediction d. a theory “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 3 of 10 Chemistry 115 Note outlines The atomic world according to Dalton..... The Components of Matter Element Molecule ♦ the simplest type of substance with unique ♦ an entity that consists of two or more atoms physical and chemical properties that are chemically bound together and thus behave as an independent unit ♦ consists of only one type of atom ♦ It cannot be broken down into any simpler substances by physical or chemical means Compound ♦ a substance composed of two or more elements which are chemically combined Mixture ♦ a group of two or more elements and/or compounds that are physically intermingled The following scenes represent an atomic-scale view of three samples of matter. Describe each sample as an element, compound, or mixture. mixture element compound “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 4 of 10 Chemistry 115 Note outlines Don’t forget to be working on memorizing all the elements and polyatomic ions listed on the syllabus! Polyatomic ions are ions consisting of a group of atoms. This group of atoms stays together as a unit in many reactions. Students should memorize the names and formulas for the following polyatomic ions. Ion Name Ion Name Ion Name 2− 2− − Acetate Chromate Sulfate C2H3O2 CrO4 SO4 + 2NH4 Ammonium Cyanide SO3 Sulfite CN− 2 − − − Bicarbonate Dichromate Nitrate HCO3 Cr2O7 NO3 + − (or hydrogen carbonate) H3O Hydronium Nitrite NO2 2− − − Peroxide Bisulfate (or hydrogen Hydroxide O2 HSO4 OH sulfate) Bisulfite (or hydrogen Permanganate PO43− Phosphate HSO3− MnO4− sulfite) Carbonate Oxalate Phosphite CO32− C2O42− PO33− Oxy anion series Ion ClO4− ClO3− ClO2− ClO− Name Perchlorate Chlorate Chlorite Hypochlorite Ion BrO4− BrO3− BrO2− BrO− Name Perbromate Bromate Bromite Hypobromite Ion IO4− IO3− IO2− IO− Name Periodate Iodate Iodite Hypoiodite Question: Of what is matter made? Answer: Chemists assert that all matter is composed of tiny particles called atoms and molecules Question: Answer: ♦ Pentacene: C22H46 [Theory- textbook] Pentacene: C22H46 [AFM-atomic force microscopy] Images courtesy of IBM Research – Zurich “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 5 of 10 Chemistry 115 Note outlines Question: Answer: ♦ Experiments from 1810 to 1910 provided evidence that atoms did exist, but suggested that they were composed of smaller (subatomic) particles Cathode-Ray Tubes: J. J. Thomson (1897) ♦ Totally changed the view of an atom by discovering the electron ♦ Thomson’s atomic theory suggested that the was composed of smaller subatomic particles − − Observation Conclusion ♦ Plum pudding model of the atom − “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 6 of 10 Chemistry 115 Note outlines Ernest Rutherford (1871-1937): Scattering experiment and discovery of the atomic nucleus ♦ Proposed a new and revolutionary concept of the atom based on his experiments − Results of these experiments were completely unexpected ♦ New model of the atom − − − Rutherford’s Gold foil experiment (http://www.youtube.com/watch?v=iuU4Ayom4b0) “You can learn a lot by throwing rocks” ♦ ♦ ♦ − “Dalton! You forgot isotopes!!!” ♦ ♦ − Subatomic Particles (summary) Relative charge −1 Relative mass 1/1800 amu Proton +1 1 amu Inside nucleus neutron 0 1 amu Inside nucleus Electron location Outside nucleus Atomic mass unit (amu) ≡ a mass equal to exactly 1/12 the mass of a carbon-12 atom “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 7 of 10 Chemistry 115 Note outlines Notes ♦ ♦ − − Isotopes ≡ atoms with same number of protons but different numbers of neutrons ♦ Isotopes of an element have slightly different weights but the same chemical properties. Notation Atomic number, Z ≡ the number of protons in an atom of an element Mass number, A ≡ the number of protons plus neutrons in an atom Concept Check Which of the following gives the correct number of protons, neutrons, and electrons for a a. b. c. d. protons 8 8 8 8 electrons 10 10 8 8 18 O −2 ion. neutrons 8 10 10 8 Concept Check In which of the following sets do all species have the same number of electrons? a. Br−, Kr, Sr2+ b. C, N3−, O2− c. Mg2+, Sr2+, Ba2+ d. O, O2−, O2+ All elements have at least two different isotopes. Since they have a different number of neutrons, they have different weights. How do we report the atomic weight of an element? We report a weighted average An example of a weighted average: Your overall course average ( ) ( ) ( ) ( ) ( ) ( ) ( ) 10% 10% 10% 10% 25% 10% 25% ave = (E1) 100% + (E2 ) 100% + (E3) 100% + (E3) 100% + (Lab ave) 100% + (HW ) 100% + (Final ) 100% “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 8 of 10 Chemistry 115 Note outlines For atomic weight % isotope 1 % isotope 2 At Wt = (mass of isotope 1) + (mass of isotope 2 ) + .... etc 100% 100% % isotope i or in mathematical language .... At Wt = ∑ (mass of isotope i ) 100% i Silver (Ag, Z = 47) has two naturally occurring isotopes, 107Ag and 109Ag. From the percent abundance provided, calculate the atomic mass of Ag. Isotope Mass (amu) Abundance (%) 107 Ag 106.90509 51.84 109 Ag 108.90476 48.16 Elements can be classified by their relative positions within the table Period ≡ a horizontal row in the periodic table s block p block Group or Family ≡ a vertical column in the periodic table d block ♦ Elements in same family have similar chemical properties f block Main group/ Representative elements≡ the s-block plus the p-block elements above the mettaloids Transition Metals ≡ the d-block elements plus the p-block elements below the mettaloids Inner Transition Metals ≡ the f-block elements “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 9 of 10 Chemistry 115 Note outlines Properties of Metals ♦ Properties of Non-metals ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ Metalloids ♦ ♦ Elements that occur as molecules under standard conditions Valence electrons ⇒ those electrons in the outermost shell (highest value of n) of an atom ♦ For representative elements this is the same as its group number ♦ For transition metals it is more complicated (not discussed until Chem 422) Octet Rule⇒ atoms tend to ionize or combine such that they achieve eight valence electrons ♦ This would be a electronic configuration the same as the nearest noble gas ♦ Ions with charges in excess of ± 3 are unstable and do not typically form Predict the monoatomic ion formed by each of the following elements Iodine (Z = 53) Aluminum (Z = 13) Calcium (Z = 20) Potassium (Z = 19) Oxygen (Z = 8) Ar (Z=18) “We are what we repeatedly do. Excellence, then, is not an act, but a habit.” Aristotle Page 10 of 10