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Chapter 2: Atoms, Molecules and Ions

Chapter 2: Atoms, Molecules and Ions. What is Chemistry. Logic. Magic. Chapt. 2.1. Atoms, Molecules and Ions. Science: Atomic Theory

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Chapter 2: Atoms, Molecules and Ions

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  1. Chapter 2: Atoms, Molecules and Ions • What is Chemistry Logic Magic Chapt. 2.1

  2. Atoms, Molecules and Ions • Science: Atomic Theory • “The strength of a science is that its conclusions are derived by logical arguments from facts that result from well-designed experiments. Science has produced a picture of the microscopic structure of the atom so detailed and subtle of something so far removed from our immediate experience that it is difficult to see how its many features were constructed. This is because so many experiments have contributed to our ideas about the atom.” B. Mahan from University Chemistry Chapt. 2.1

  3. Atoms, Molecules and Ions • Science: Atomic Theory • from a fundamental understanding of the macroscopic behavior of substances comes an understanding the microscopic behavior of atoms and molecules (Baseball rules from Baseball Game?) Macroscopic Microscopic Substances Atomic theory Mixtures Physical Properties and Changes Question: Can matter be infinitely divided? Most Greek Philosophers - Yes Democritus (460 BC) and John Dalton (1800s) - No (“atomos”means indivisible”) Chapt. 2.1

  4. Atoms, Molecules and Ions • History of Atomic Theory and Scientific Inquiry • Aristotle - “metaphysics”, thought experiments and no experimental observations necessary to substantiate ideas. • Archimedes (287 - 212 BC) - Scientific Method, determined composition of the King of Syracuse’s crown by measuring density through water displacement. • Roger Bacon (1214 - 1294) - Experimental Science “ It is the credo of free men - the opportunity to try, the privilege to err, the courage to experiment anew. ...experiment, experiment, ever experiment”. Chapt. 2.1

  5. Archimedes (287-212BC) • Archimedes was a native of Syracuse (not NY). Stories from Plutarch, Livy, and others describe machines invented by Archimedes for the defence of Syracuse (These include the catapult, the compound pulley and a burning-mirror). • Archimedes discovered fundamental theorems concerning the centre of gravity of plane figures and solids. His most famous theorem gives the weight of a body immersed in a liquid, called Archimedes' principal. • His methods anticipated integral calculus 2,000 years before Newton and Leibniz.

  6. Archimedes (287-212BC)

  7. Archimedes (287-212BC) Suspecting that a goldsmith might have replaced some of the gold by silver in making a crown, Hiero II, the king of Syracuse, asked Archimedes to determine whether the wreath was pure gold. The wreath could not be harmed since it was a holy object. The solution which occurred when he stepped into his bath and caused it to overflow was to put a weight of gold equal to the crown, and known to be pure, into a bowl which was filled with water to the brim. Then the gold would be removed and the king's crown put in, in its place. An alloy of lighter silver would increase the bulk of the crown and cause the bowl to overflow. Pure Gold? Equal Weight of Gold Crown Displaced More Water

  8. Greek Philosophers Air Fire • Democratus - First to say that all matter is NOT infinately divisible. [But the Greeks did not test their ideas] • Alchemy - Pseudoscience by fakes and mystics devoted to turning base metals to gold BUT they did make (by accident) many ground breaking discoveries of nature (chemical reactions). Greek “Elements” Water Earth

  9. Scientific Measurement Robert Boyle - Robert Boyle (1627-1691) was born in Ireland. He became especially interested in experiments involving air and developed an air pump with which he produced evacuated cylinders. He used these cylinders to show that a feather and a lump of lead fall at the same rate in the absence of air resistance. In his book “The Sceptical Chemist” (1661), Boyle urged that the ancient view of elements as mystical substances should be abandoned and that an element should instead be defined as anything that cannot be broken down into simpler substances.

  10. Scientific Measurement • Antoine Lavoisier (1743 - 1794) - Furthered measurement as basis for scientific reasoning. • “Je Veux Parler Des Faits” - Do Not Rely Upon Speculation But Build Upon Facts. More on Lavoisier on Next Slide

  11. Antoine Lavoisier Antoine Lavoisier was born in Paris, and although Lavoisier's father wanted him to be a lawyer, Lavoisier was fascinated by science. From the beginning of his scientific career, Lavoisier recognized the importance of accurate measurements. He wrote the first modern chemistry (1789) textbook so that it is not surprising that Lavoisier is often called the father of modern chemistry. To help support his scientific work, Lavoisier invested in a private tax-collecting firm and married the daughter of one of the company executives. Guillotined for his tax work in 1794.

  12. Atoms, Molecules and Ions Earth • History Atomic Theory and Scientific Inquiry • Lavoisier (1743 - 1794) - founder of “modern chemistry”, not to rely on speculation but to build upon facts, ended the “time of alchemy”. Alchemy Water Fire “earth” pure water evaporate out water from dust sealed container alchemists said that the water was “transmuted” to earth Law of Conservation of Mass Lavoisier showed that the amount of “earth” found at the end of the experiment was equal to the weight the container lost, therefore, the water was not “transmuted” to earth. Chapt. 2.1

  13. Scientific Method Form and test hypothesis Patterns and Trends Theory Observations and Experiments Chapt. 2.1

  14. John Dalton (1766-1844) John Dalton (1766 -1844), an Englishman, began teaching school when he was 12. He was fascinated with meteorology (keeping daily weather records for 46 years), which led to an interest in gases and their components, atoms. He switched to chemistry when he saw applications in chemistry for his ideas about the atmosphere. He proposed the Atomic Theory in 1803. Dalton was a humble man with several apparent handicaps: he was poor; he was not articulate; he was not a skilled experimentalist, and he was color-blind (a terrible problem for a chemist). In spite of these disadvantages he did great things.

  15. Atomic Theory • John Dalton’s Atomic Theory • Designed a theory to account for a variety of experimental observations: • Each element is composed of extremely small particles (called atoms). • All atoms of a given element are identical (therefore, atoms of different elements are different and have different properties). Chapt. 2.1

  16. Atomic Theory (Continued) • John Dalton’s Atomic Theory • Atoms of an element are not changed into different types of atoms by chemical reactions and atoms are neither created nor destroyed in chemical reactions. • Compounds are formed when atoms combine and a given compound always has the same relative number and kind of atoms. Chapt. 2.1

  17. Atomic Theory • Dalton’s Atomic Theory • Atoms are the building blocks: • Elements are composed of only one kind of atom. • Compounds are made by mixing atoms in definite proportions • Mixtures do not involve the type of “small scale” (but strong) interactions found in Elements and Compounds Chapt. 2.1

  18. Atomic Theory; Dalton’s Theories • Law of Constant Composition (or Definite Proportion, first proposed by Joseph Proust): • In any given compound, the relative number and kind of atoms are constant (same proportion of elements by mass). • implies that atoms interact in a specific way when they form a compound. • the elements making up a particular compound combine in the same proportions regardless of the manner in which the compound was prepared. Chapt. 2.1

  19. Atomic Theory; Dalton’s Theories • Law of Constant Composition (or Definite Proportion): Copper Carbonate ALWAYS contains 5.3 parts Copper to 4 parts Oxygen and 1 part Carbon (by Weight). Carbon Dioxide ALWAYS contains 1.00 parts Carbon to 2.67 parts Oxygen Chapt. 2.1

  20. Atomic Theory; Dalton’s Theories • Law of Conservation of Mass: • the total amount of material present after a chemical reaction is the same as the amount present before the reaction. Matter (elements, etc...) cannot be created nor destroyed during chemical reactions. Total Mass Before Chemical Reaction Total Mass After Chemical Reaction = Chapt. 2.1

  21. Guy-Lussac Joseph Guy-Lussac (1778 - 1850) found that (at the same temperatures and pressures): 2 volumes of hydrogen reacts with 1 volume of oxygen to yield 1 volume of water vapor = + Water O H Amedeo Avogadro (1776 - 1856) proposed that (at the same temperatures and pressures), equal volumes of different gases contain the same number of particles: 2 molecules of H + 1 molecule of O yield 1 molecule of water

  22. Experiments in Atomic Theory Dalton’s Laws Set Groundwork for Atomic Theory but Important Experiments Lead to Our Modern Understanding • Faraday - Electrodeposition • Millikan - Oil Drop Experiment • Roetgen - Radioactivity • Curie - Radioactive Particles • Rutherford - Gold Foil Experiment

  23. Michael Faraday (1791-1867) Experiments in electro-magnetism, electrical power conversion, etc... Humble scientist rose from very poor background to become one of the most influential of his age. Believed that careful observations were most important. “Try desperately to succeed - and do not hope for success”

  24. Electrodeposition Cell electrodes - + deposition electrolyte Atomic Structure • Electrical Nature • Michael Faraday (1833) (first ideas about the nature of electricity • The weight of a material deposited at an electrode by a given amount of electricity is always the same. • The weights of various materials deposited by fixed amounts of electricity are proportional to their equivalent weights. [remember equivalent weights] Chapt. 2.1

  25. Sir J. J. Thomson British physicist who worked with electrical currents and fields. Appointed Prof. of Physics at Cambridge when he was 27 and Received the Nobel Proze in 1906 for his characterization of the electron.

  26. Atomic Structure • J. J. Thomson: Cathode Ray Tube (CRT) Experiment • Set up a large electrical potential between a pair of electrodes in a glass tube and an electrical current will flow between the elctrodes. • The current will flow even when all the air is pumped out of the tube. The invisible charge carriers were called “cathode rays”. • Cathode rays travel in straight lines and form a luminious spot when they hit a glass tube. (-) (+) Cathode Ray Tube [evacuated glass tube] Chapt. 2.1

  27. Atomic Structure: CRT The cathode rays are deflected by an electric field. (-) (+) Electric Field The cathode rays are deflected by an magnetic field. (-) (+) The same effect was observed regardless of what gas was used in the discharge tube. Therefore, electricity must be a universal fragment. Magnetic Field Chapt. 2.1

  28. Electricity: Thomson’s charge to mass (-) CRT (+) 1 2 3 (-) (+) Magnetic Field Electric Field • Spot mag field elec. field • 1 On Off • 3 Off On • 2 Off Off • On On Chapt. 2.1

  29. Thomson’s charge to mass Ee = Electrical Field He = Magnetic Field [where e = electric charge (unk) and  = velocity] Set up experiment such that; Electrical Field = Magnetic Field Ee = He or E / H Now, turn off the mag. field and measure deflection of beam () Using Newton’s 2nd Law can calculate e/m (-) CRT (+) 1 2 3 (-) (+) Magnetic Field

  30. Thomson’s charge to mass calculated charge to mass ratio (e/m) for electron = 1.76 x 108 coulombs/g found; (1) e/m was 1000x greater than for any known ion (2) e/m of independent of gas in tube [Universal Fragment] (3) Not electrified atoms but fragments (called electrons)

  31. Robert Millikan (1868-1953) Nobel Prize, 1923; for his work on the elementary charge of electricity and on the photoelectric effect. Robert Millikan was one of the first American scientists to be recognized in Europe. In 1909 he performed the first of a series of experiments to measure the fundamental charge of an electron, the Millikan Oil Drop Experiment. The value determined by this experiment was used in Bohr's formula for the energy of the Hydrogen line spectrum as a first confirmation of the quantized atom. He named and studied "cosmic rays" as well.

  32. Electricity: Millikan’s electron mass Oil Drop Experiment (1909) Goal: to measure the electrical charge on each oil droplet Procedure: measure the velocity of the falling oil drop both with and without the high voltage plates urned on Found: charges were always multiples of 1.60 x 10-19 C Postulate: charge of one electron was 1.60 x 10-19 C atomizer - high voltage viewer + Ionization by radiation causes the oil to pick up “extra” electrons Chapt. 2.1

  33. Thomson Millikan Electricity: electron mass charge = e = 1.76 x 108 coul g-1 mass m mass of the electron was 2000x smaller than the lightest atom (hydrogen) charge = e = 1.60 x 10-19 coul Combine and Solve mass = charge = 1.60 x 10-19 C = 9.10 x 10-28 g 1.76 x 108 coul g-1 1.76 x 108 C g-1 Chapt. 2.1

  34. Wilhelm Conrad Roentgen Wilhelm Conrad Roentgen was born in Lennep, Germany, on 27 March 1845. He obtained a degree in mechanical engineering and, in 1869, was awarded a degree in physics. While working as a professor of physics at Wurzburg University, he made his famous discovery. He called the unknown radiation "X rays," since "X" frequently stands for an unknown quantity in mathematics. His unique discovery truly changed the world and immediately became a useful tool for medical science. Wilhelm Conrad Roentgen

  35. U Radioactivity: Wilhelm Roetgen and Henri Becquerel metal target CRT X-rays - not affected by magnetic fields - passed thru many materials -produced images on film (ionized Ag emulsions) e beam invisible radiation (X-rays) glowed in dark (phosphorescence) emitted high energy radiation in the dark (radioactivity) Chapt. 2.1

  36. 1903 Nobel Prize for Radioactivity Pierre and Marie Curie Henri Becquerel

  37. Marie Sklodawaska Curie The most famous of all women scientists, Marie Sklodowska-Curie is notable for many firsts. In 1903, she became the first woman to win a Nobel Prize for Physics (Pierre Curie and Henri Becquerel, for the discovery of radioactivity. She was also a professor at the Sorbonne University in Paris (1906). In 1911, she won an unprecedented second Nobel Prize (in chemistry for her discovery radium. She was the first person ever to receive two Nobel Prizes.) She was the first mother of a Nobel Prize Laureate; daughter- Nobel Prize 1932. Marie Sklodowska-Curie In 1934, Maria Curie died of leukemia

  38. U Radioactivity: Marie Curie and Ernest Rutheford • Marie Curie (1867 - 1934) - separated the pure radioactive material (Uranium) which was spontaneously radioactive (from the mineral pitchblende) • Ernest Rutheford (1871 - 1937) - found radiation from uranium was of three types (, , and )  -  + slits  •  - heavy particles with +2 charge, combines with electrons • to form helium, 4He •  - electrons with -1 charge •  - high energy electromagnetic radiation Chapt. 2.1

  39. Nuclear Atom: Thomson’s Model (ca. 1900) • Since the electron made up only a small amount of an atom’s mass it was proposed that it must similarly make up a small amount of the atoms volume. “Plum-pudding” model positive charge spread over sphere = electron

  40. Ernest Rutherford Ernest Rutherford (1871-1937) was born on a farm in New Zealand. In 1895 he placed second in a scholarship competition to attend Cambridge University, but was awarded the scholarship when the winner decided to stay home and get married. As a scientist in England, Rutherford did much of the early work on characterizing radioactivity. He also invented the name proton for the nucleus of the hydrogen atom. He received the Nobel Prize in chemistry in 1908.

  41. Nuclear Atom: Rutheford and the Gold Foil experiment - fired heavy  particles at a thin gold foil and looked for deflections   4He particles thin gold foil slits detector • found - most particles passed straight through foil, some had • deflections thru small angles BUT some had VERY • large deflections ( = 180°) “...as if you fired a 15-inch cannon shell at a piece of tissue paper and it came back and hit you...”

  42. Nuclear Atom: Rutheford and the Gold Foil Gold Foil A:C around 13,000:1 A  Beam A C B B A A

  43. Rutheford’s Atom Based on gold foil experiment and previous work with electrical and nuclear particles, proposed a nuclear theory; (1) atoms are mostly empty space with very dense (pos. charged) nuclear core (<10-12 cm dia.) (2) atoms are highly “non-uniform” (3 ) atomic nucleus must contain large electrical forces of considerable mass (since small electron cannot be responsible for such large deflections)

  44. + + + + Nature’s Basic Forces • Electromagnetic - force between charged or magnetic particles (electrical and magnetic forces are very closely related). DRIVES MOST OF CHEMICAL BEHAVIOR (Coulomb’s Law; F = kQ1Q2/d2) • Gravitational - force between objects proportional to their masses. • Strong Nuclear - force keeping like charged nucleons (such as protons) together (very strong but very short range). • Weak Nuclear - nuclear force observed in some radioactive behavior (weaker than electromagnetic but stronger than gravitational). + - m m Strong Nucl. > Electromagnetic > Weak Nucl. > Gravitational

  45. Modern Atomic Structure • atomic dimensions; nucleus 10-4 Å and atom 1 - 2 Å (1 Å = 10-10 m) “... if a nucleus were 2 cm (ca. 1 in.) then the atom would be 200 m (ca. 200 yds)” • atom composed of many “subatomic” particles but only three of these are important to chemists • atomic mass (1 amu = 4 x 10-22 g), charge (1 esc = 1.60 x 10-19 coul), density (1014 g/cm3) • atom = dense nucleus with mostly empty space; electrons of most chemical import. (matchbox of nucl. = 2.5 billion tons) particle charge (esu) mass (amu) proton +1 1.0073 neutron 0 1.0087 electron -1 5.486 x 10-4

  46. Atomic Theory: Isotopes • differences/similarities between atoms of an element; • all atoms of an given element have the same number of protons (and therefore the same number of electrons to balance charge) • atoms of an element may have different numbers of neutrons - called isotopes AE 11C 12C 13C 14C Z 6 6 6 6 atomic number (Z) - number of protons mass number (A) - number of protons + number of neutrons nuclide - atoms of a specific elemental isotope

  47. Atomic Theory: Isotopes • 7 electrons, 7 protons, 7 neutrons • 8 electrons, 8 protons, 9 neutrons • 17 electrons, 17 protons, 18 neutrons • 92 electrons, 92 protons, 146 neutrons 14N 7 17O 8 35Cl 17 238U 92

  48. Atomic Theory: Isotopes Sample exercise:How many protons, neutrons, and electrons are in a 39K atom?

  49. Atomic Theory: Isotopes Sample exercise:How many protons, neutrons, and electrons are in a 39K atom? Atomic# = 19 # of protons = 19 # of electrons = 19 Mass # = 39 39 - 19 = 20 neutrons

  50. Atomic Theory: Isotopes Sample exercise:Give the complete chemical symbol for the nuclide that contains 18 protons, 18 electrons, and 22 neutrons.

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