Chapter 2 : Atoms, Molecules, and Ions

Parmenides (BC 515? BC 445?) : < 있는것 ( 토에온 )> 은있고 < 없는것 ( 토메에온 )> 은없다고하는전제 ( 前提 ) 에서불생불멸 불가분 불변부동이며, 완결된둥근공과비슷하다고하는 < 있는것 > 의속성을끌어내고, < 있는것 > 을우리에게보여주는이성만이진리를포착하며생성 소멸또는변화를믿게하는감각은오류의근원. (1 원론 ) 이오니아학파 (BC 5 세기 ) : 불 공기 물 (3 원소설 ) 엠페도클레스 (BC 5 세기 ) : 불 공기 물 흙 (4 원소설 ) 변화 <= 불 공기 물 흙 + 사랑, 미움 Early Question: Is matter continuous or noncontinuous? Demokritos (BC 4 세기 ) : atomos (noncontinuous) Plato, Aritotle : continuous

Before 16th Century 17th Century 18th Century 19th Century Alchemy: Attempts (scientific or otherwise) to change cheap metals into gold Robert Boyle: First chemist to perform quantitative experiments "The Skeptical Chemist" - Substance is an element unless it can be broken down into two or more simpler substances. (Noncontinuous) George Stahl: Phlogiston flows out of a burning material. Joseph Priestley: Discovers oxygen gas, dephlogisticated air. More Studies on combustion : found Carbon Dioxide, Nitrogen, Hydrogen, Oxygen Antoine Lavoisier: Combustion: not Phlogiston, but oxygen Law of Conservation of Mass

19th Century Joseph Proust: Law of Definite Proportion A given compound always contains exactly the same proportion of elements by mass. Copper carbonate always contains 5.3 parts copper to 4 parts oxygen to 1 part carbon (by mass). Stimulated John Dalton : atoms as the particle that might compose elements. (Hyposesis) John Dalton : Law of Multiple Proportion When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can be always be reduced to small whole number.

Mass of Nitrogen that combinds with 1g of Oxygen Compound A 1.750g 4 Compound B 0.8750g 2 Compound C 0.4375g 1 Case Stimulated 1: John Dalton : atoms as the particle that might compose Elements. (Hyposesis) Oxygen Case 2: John Dalton : Law of Multiple Proportion Nitrogen When two elements form a series of compounds, the ratios Infinite of the masses possible of combinations, the masses of but the supports second element John Dalton s hyposesis that combine that each with elements 1 gram consist of the of first certain Element type can of atom be and that always compounds be reduced were to small formed whole from number. specific combinations of atoms.

19th Century John Dalton: Atomic Theory (In New System of Chemical Philosophy, 1808) 1. Each element is made up of tiny particles called atoms. 2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways. 3. Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms. (Laws of Definite and Multiple Proportion) 4. Chemical reactions involve reorganization of the atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction. (Law of Conservation of Mass)

19th Century John Dalton: Atomic Theory (In New System of Chemical Philosophy, 1808) Water : 1 gram of hydrogen and 8 gram of oxygen?? OH (H: mass 1, O: mass 8) or H 2 O (H: mass 1, O: mass 16) Dalton s assumption: Nature must be simple. => OH Gay-Lussac s Observation (Gas)

19th Century Avogadro s Hyposesis: At the same temperature and pressure, equal volumes of different gases contain the same number of particles. 5 liters of oxygen, 5 liters of nitrogen => Same number of particles 2 molecules of hydrogen + 1 molecule of oxygen ==> 1 molecule of water correct formula is obtained as H 2 O

Now people believe in atoms. Then what does it look like? 1820 M. Faraday: Electrolysis Determined e/m ratios of many ions e/m for H + = 10 8 C/kg

1885 E. Goldstein : positively charged sub-atomic particle 1885 Balmer: Hydrogen spectrum 1898-1903 J. J. Thomson: Cathod-ray tube experiment something out of cathod : electron (e - ) neutrality of matter

1885 E. Goldstein : positively charged sub-atomic particle 1885 Balmer: Hydrogen spectrum 1898-1903 J. J. Thomson: Cathod-ray tube experiment F mag = q v x B F el = q E e/m for e - = ~ -1.2x10 11 C/kg (currenytly, 1.76x10 11 C/kg) e/m for H + = 10 8 C/kg Either the electron has a far greater charge than the proton, or it has far less mass.

1909 R. Millikan : Oil-droplet experiment mg = qe q = n x 1.60 x 10-19 C e - = -1.60 x 10-19 C e/m for e - = -1.2x10 11 C/kg m e = 1.3x10-30 kg (currently, 9.11 x 10-31 kg) e/m for H + = 10 8 C/kg m p = 1.2x10-27 kg (currently, 1.67 x 10-27 kg)

Meantime Understanding radioactivity Found certain elements produce high-energy radiation. g-ray : high-energy light b-particle : high-speed electron a-particle : positivley charged particle (charge = -2 x e -, mass = 7300 x m e ) (nucleus of He)

1911 E. Rutherford : Backscattering experiment

The Modern View of Atomic Structure: An Introduction Atom Protons Neutrons Electrons Nucleus Atom

The Modern View of Atomic Structure: An Introduction What makes differences? Number of protons (or electrons) Sodium Isotopes (atoms with same number of protons but different number of neutrons) Mass number (= # of protons + # of neutrons) Atomic number (= # of protons) 23 11Na Sodium-23 Element Symbol 24 11Na Sodium-24

Molecules and Ions Chemical Bonding creates The forces that hold atoms together in compounds. Covalent bonds result from atoms sharing electrons. Diversity in the Universe Metallic bonds Ionic bonds Molecule : a collection of covalently-bonded atoms. Methane Chemical Formula: Symbols = types of atoms Subscripts = relative numbers of atoms (CH 4 ) Structural Formula: Individual bonds are shown by lines.

Molecules and Ions Covalent bonds result from atoms sharing electrons. Metallic bonds Ionic bonds : Force of attraction between oppositely charged ions. Cation: A positive ion (Ex: Na +, Mg 2+, NH 4+ ) Anion: A negative ion (Ex: Cl -, SO 4 2- ) Na(s) Cl 2 (g) NaCl(s) 11 p + - e - 11 p + 11 e - 10 e - Na Na + + e - 17 p + 17 p + + e - 17 e - 18 e - Cl + e - Cl -

An Introduction to the Periodic Table Periodic Table: Elements classified by properties and atomic number Metal Nonmetal Family (Group) Period Chemical Bonding creates Diversity in the Universe rearrangement of atoms and molecules

Naming Simple Compounds More than 5,000,000 chemicals are known. Common name Systematic name Naming Binary Ionic Compounds (Type I) 1. Cation first, then anion 2. Monatomic cation = name of the element (ex) Ca 2+ => calcium 3. Monatomic anion = root + -ide (ex) Cl - => chloride CaCl 2 = calcium chloride, NaCl = sodium chloride, KI = potassium iodide Binary compounds: compounds composed of two elements.

Naming Simple Compounds Naming Binary Ionic Compounds (Type II) 1. Metal forms more than one cation. 2. Use Roman numeral in name to specify the charge of the cation (Or The higher charge has a name ending in ic, and the one with the lower charge has a name ending in ous.) Ex) (charge balance to determine the cation charge!!) CuCl = copper(i) chloride, CuCl 2 = copper(ii) chloride Fe 2 O 3 = iron(iii) oxide, CoBr 2 = cobalt(ii) bromide CaCl 2 = calcium chloride, Al 2 O 3 = aluminum oxide CrCl 3 = chromium(iii) chloride

Naming Simple Compounds Naming Ionic Compounds with Polyatomic Ions Memorize!! Oxyanion -ite -ate -hypo (less than) -per (more than) CuSO 4 Ex) Na 2 SO 4 = sodium sulfate KH 2 PO 4 = potassium dihydrogen phosphate CuSO 4 = copper(ii) sulfate KBrO 3 = potassium bromate

Naming Simple Compounds Naming Binary Covalent Compounds (Type III) Compounds between two nonmetals 1. First element in the formula is named first. 2. Second element is named as if it were an anion. 3. Use prefixes. Never use mono- for the first element. Ex) CO = carbon monoxide, PCl 3 = phosphous trichloride NO 2 = nitrogen dioxide, N 2 O 3 = dinitrogen trioxide P 2 O 5 = diphosphorus pentoxide

Naming Simple Compounds Acids Produces H + when dissolved in water. Composed of H + and anion.