Chapter 2Atoms, Molecules and IonsChapter Learni

Chapter 2Atoms, Molecules and IonsChapter Learning Goals : Chapter 2 Atoms, Molecules and Ions Chapter Learning Goals Fundamental Chemical Laws and Atom. Modern View of Atomic Structure, Molecules, and Ions. Periodic Table. Naming Simple compounds, Ionic compounds, Formula from names.

The Early History of Chemistry : The Early History of Chemistry Before 16th Century Alchemy: Attempts (scientific or otherwise) to change cheap metals into gold 17th Century Robert Boyle: First “chemist” to perform quantitative experiments 18th Century George Stahl: Phlogiston flows out of a burning material. Joseph Priestley: Discovers oxygen gas, “dephlogisticated air.”

Law of Conservation of Mass : Law of Conservation of Mass Discovered by Antoine Lavoisier Mass is neither created nor destroyed Combustion involves oxygen, not phlogiston

Other Fundamental Chemical Laws : Other Fundamental Chemical Laws A given compound always contains exactly the same proportion of elements by mass. Carbon tetrachloride is always 1 atom carbon per 4 atoms chlorine: CCl4 Water is always 1 atom Oxygen per 2 atoms Hydrogen: H2O Law of Definite Proportion

Other Fundamental Chemical Laws : Other Fundamental Chemical Laws 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 always be reduced to small whole numbers. The ratio of the masses of oxygen in H2O and H2O2 will be a small whole number (“2”). Law of Multiple Proportions

Slide6 : The ratio of the masses of oxygen in Cr2O3 and CrO3 will be a small whole number. Cr2O3 contains 2.167 g Cr/ g of Oxygen CrO3 contains 1.083 g Cr/ g of Oxygen The ratio is 2.167/1.083 = 2:1 Another Example:

Slide7 : 2.1

Slide8 : Mass of Nitrogen That Combines With 1 g Oxygen Compound A 1.750 g Compound B 0.8750 g Compound C 0.4375 g A/B = 1.750/0.8750 = 2/1 B/C = 0.875/0.4375 = 2/1 A/C = 1.750/0.4375 = 4/1 i.e. amount of nitrogen in A is twice that in B, etc.

Dalton’s Atomic Theory (1808) : Dalton’s Atomic Theory (1808) Each element is made up of tiny particles called atoms. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.

Dalton’s Atomic Theory(continued) : Dalton’s Atomic Theory (continued) Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms. 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.

Dalton's theory lead to: : Dalton's theory lead to: 1gm hydrogen + 8gm of oxygen water he assumed that water formula is "OH" and the mass of hydrogen is "1" and of oxygen is "8". Using the same concepts, Dalton's proposed the first table of atomic masses. It has been proved later that Dalton's table contain incorrect. Gay-lussac (1778-1850) found experimentally that:

Slide12 : Figure 2.4: A representation of some of Gay-Lussac's experimental results on combining gas volumes. Interpreted in 1811 by Avogadro

Avogadro’s Hypothesis (1811) : Avogadro’s Hypothesis (1811) 5 liters of oxygen 5 liters of nitrogen Same number of particles! At the same temperature and pressure, equal volumes of different gases contain the same number of particles.

Slide14 : Figure 2.5: A representation of combining gases at the molecular level. The spheres represent atoms in the molecules.

Early Experiments to Characterize the Atom : Early Experiments to Characterize the Atom J. J. Thomson - postulated the existence of electrons using cathode ray tubes. Measured mass/charge of e- Received 1906 Nobel Prize in Physics e = -1.76 x 108 C/g m

Figure 2.7: A cathode-ray tube. The fast-moving electrons excite the gas in the tube, causing a glow between the electrodes. : Figure 2.7: A cathode-ray tube. The fast-moving electrons excite the gas in the tube, causing a glow between the electrodes.

Slide17 : 2.2

Slide18 : (Uranium compound)

Figure 2.9: Thomson plum pudding model of the atom. : Figure 2.9: Thomson plum pudding model of the atom.

Slide20 : Ernest Rutherford - explained the nuclear atom, containing a dense nucleus with electrons traveling around the nucleus at a large distance.

Slide21 : Figure 2.12: Rutherford's experiment on -particle bombardment of metal foil.

Slide22 : Figure 2.13: (a) The expected results of the metal foil experiment if Thomson's model were correct. (b) Actual results.

Millikan oil drop experiment : Millikan oil drop experiment Millikan did another experiment to determine the mass of the –ve particles (electrons). The experiment used mainly to determine the magnitude of the electron charge and using e/m to get m- value.

The Modern View of Atomic Structure : The Modern View of Atomic Structure electrons protons: found in the nucleus, they have a positive charge equal in magnitude to the electron’s negative charge. neutrons: found in the nucleus, virtually same mass as a proton but no charge. The atom contains:

Slide25 : Figure 2.14: A nuclear atom viewed in cross section. Note that this drawing is not to scale.

Slide26 : Figure 2.15: Two isotopes of sodium. Both have eleven protons and eleven electrons, but they differ in the number of neutrons in their nuclei.

The Mass and Charge of the Electron, Proton, and Neutron : The Mass and Charge of the Electron, Proton, and Neutron

Summary : Summary J.J. Thompson (1897) “cathode rays are electrons” (e–) and finds e/m ratio Robert Millikan (1909) measures e and hence melectron known at 9.1110-31 kg E. Rutherford (1906) bounces  (He2+) off Au tissue proving protons (p+) in nucleus F.A. Aston (1919) “weighs” atomic ions J. Chadwick (1939) observes neutrons (no charge) by decomposition (to p+, e–, and ).

The Chemists’ Shorthand: Atomic Symbols : The Chemists’ Shorthand: Atomic Symbols K  Element Symbol 39 19 Mass number  Atomic number 

Chemical Bonds : Chemical Bonds The forces that hold atoms together in compounds. Covalent bonds result from atoms sharing electrons. Molecule: a collection of covalently-bonded atoms.

The Chemists’ Shorthand:Formulas : The Chemists’ Shorthand: Formulas Chemical Formula: Symbols = types of atoms Subscripts = relative numbers of atoms CO2 Structural Formula: Individual bonds are shown by lines. O=C=O

Slide32 : Figure 2.16: The structural formula for methane.

Slide33 : Figure 2.17: Space-filling model of methane. This type of model shows both the relative sizes of the atoms in the molecule and their spatial relationships.

Slide34 : Figure 2.18: Ball-and-stick model of methane.

Ions : Ions Cation: A positive ion Mg2+, NH4+ Anion: A negative ion Cl, SO42 Ionic Bonding: Force of attraction between oppositely charged ions.

Periodic Table : Periodic Table Elements classified by: properties  atomic number Groups (vertical) 1A = alkali metals 2A = alkaline earth metals 7A = halogens 8A = noble gases Periods (horizontal)

Slide38 : Figure 2.21: The Periodic Table. http://center.acs.org/periodic/tools/pt.html

Naming Compounds : Naming Compounds 1. Cation first, then anion 2. Monatomic cation = name of the element Ca2+ = calcium ion 3. Monatomic anion = root + -ide Cl = chloride CaCl2 = calcium chloride HI = hydrogen iodide Binary Ionic Compounds:

Slide40 : Figure 2.19: Sodium metal reacts with chlorine gas to form solid sodium chloride.

Naming Compounds(continued) : Naming Compounds (continued)  metal forms more than one cation (Usually Transition Metals)  use Roman numeral in name PbCl2 Pb2+ is cation PbCl2 = lead (II) chloride Binary Ionic Compounds (Type II):

Slide42 : FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride Cr2S3 3 S2- -6 so Cr is +3 (6/2) chromium(III) sulfide

Slide43 : Figure 2.22: The common cations and anions

Naming Compounds(continued) : Naming Compounds (continued)  Compounds between two nonmetals  First element in the formula is named first.  Second element is named as if it were an anion.  Use prefixes  Never use mono- P2O5 = diphosphorus pentoxide Binary compounds (Type III):

Slide45 : NF3 nitrogen trifluoride SO2 sulfur dioxide N2Cl4 dinitrogen tetrachloride NO2 nitrogen dioxide N2O dinitrogen monoxide Molecular Compounds 2.7

Slide49 : EXCEPTION IN BINARY IONIC COMPOUNDS TYPE II ELEMENTS FORMING ONLY ONE CATION: NO ROMAN NUMERALS (I,II,III….) ALL GROUP I AND GROUP II ELEMENTS Al3+, AlCl3 ALUMINIUM CHLORIDE Ag+, AgCl, SILVER CHLORIDE Zn2+, ZnSO4, ZINC SULPHATE Cd2+, CdCl2, CADMIUM CHLORIDE

Slide51 : NO3- & NO2- Nitrate Nitrite SO4-- & SO3-- Sulfate Sulfite OXYANIONS  Several series of ANIONS: an atom with different numbers of Oxygen atoms.  Anion with smaller number of Oxygen ends in –ite  Anion with larger number of Oxygen ends in –ate

Slide52 : OXYANIONS OF MORE THAN 2 OXYGEN ATOMS  Anion with smaller number of Oxygen ends in –ite  Anion with larger number of Oxygen ends in –ate ClO- ClO2- ClO3- ClO4- CHLORITE CHLORATE HYPOCHLORITE PERCHLORATE WE CAN ALSO USE THESE NAMES FOR Br AND I

Slide53 : Figure 2.23: A flowchart for naming binary compounds.

Slide54 : Figure 2.24: Overall strategy for naming chemical compounds.

Slide55 : ACIDS AN ACID CONTAINS ONE OR MORE H+ ION  Anion without Oxygen, starts with hydro– & ends –ic HCl,hydrochloric, HCN, hydrocyanic, H2S, hydrosulphuric ClO- ClO2- ClO3- ClO4- CHLORITE CHLORATE HYPOCHLORITE PERCHLORATE  Anion with Oxygen, name ends with root name: Anion –ate changes to acid –ic SO42-, H2SO4 Sulphuric acid, NO3-, HNO3 Nitric acid Anion –ite changes to acid –ous SO32-, H2SO3 Sulphurous acid, NO2-, HNO2 Nitrous acid

Slide58 : Acid Anion Name HClO Hypochlorite Hypochlorous acid HClO2 Chlorite Chlorous acid HClO3 Chlorate Chloric acid HClO4 Perchlorate Perchloric acid

Slide59 : Figure 2.25: A flowchart for naming acids. An acid is best considered as one or more H+ ions attached to an anion.

Naming Exercise : Naming Exercise Al2(S2O3)3 P4O10 Cu(NO2)2 NaMnO4 CS2 Fe2(CrO4)3 HCl (gas) PH4BrO2 Aluminum thiosulfate Tetraphosphorous decaoxide Copper(II) nitrite Sodium permanganate Carbon disulfide Iron(III) chromate Hydrogen chloride Phosphonium bromite