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The Early History of Chemistry

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1 The Early History of Chemistry
Before 16th Century Alchemy: Attempts to change cheap metals into gold; did discover several elements 17th Century Robert Boyle: First “chemist” to perform quantitative experiments; measured relationship between P and V of air 18th Century Joseph Priestley: Discovers oxygen gas, isolated oxygen by heating mercuric oxide Copyright©2000 by Houghton Mifflin Company. All rights reserved.

2 Law of Conservation of Mass
Mass is neither created nor destroyed Discovered by Antoine Lavoisier Combustion involves oxygen Life is supported by a process that involves oxygen and is similar to combustion Copyright©2000 by Houghton Mifflin Company. All rights reserved.

3 Other Fundamental Chemical Laws
Law of Definite Proportion A given compound always contains exactly the same proportion of elements by mass. Carbon tetrachloride is always 1 atom carbon per 4 atoms chlorine. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

4 Other Fundamental Chemical Laws
Law of Multiple Proportions 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”). Copyright©2000 by Houghton Mifflin Company. All rights reserved.

5 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
NO g N / 1 g O N2O g N / 1 g O NO g N / 1 g O Copyright©2000 by Houghton Mifflin Company. All rights reserved.

6 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. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

7 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. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

8 Avogadro’s Hypothesis (1811)
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! Copyright©2000 by Houghton Mifflin Company. All rights reserved.

9 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Dalton’s Model of the Atom: a solid sphere Copyright©2000 by Houghton Mifflin Company. All rights reserved.

10 Early Experiments to Characterize the Atom
J. J. Thomson - postulated the existence of electrons using cathode ray tubes. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

11 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Since atoms were electrically neutral, must have some (+) charge Thomson proposed that atoms were (+) charged clouds with (-) electrons embedded in them This is called the “plum-pudding model” Copyright©2000 by Houghton Mifflin Company. All rights reserved.

12 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Thompson also determined the charge to mass ratio of the electron Robert Millikan determined the magnitude of the electron charge; oil drop experiment Millikan combined the charge to mass ratio with the magnitude of the charge to find the mass of an electron Mass of an electron = 9.11 x 10-31g Copyright©2000 by Houghton Mifflin Company. All rights reserved.

13 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

14 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Henri Becquerel – discovered radioactivity Early 20th century experiments demonstrate three types of radioactive emission: Gamma rays – high energy elecromagnetic radiation Beta particles – high speed electrons Alpha particles - +2 charge (2 protons and 2 neutrons) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

15 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Ernest Rutherford – Gold foil experiment which explained the nuclear atom, containing a dense nucleus with electrons traveling around the nucleus at a large distance. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

16 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Rutherford also Named alpha, beta and gamma particles Coined the term half-life Invented the name proton for the nucleus of the hydrogen atom Copyright©2000 by Houghton Mifflin Company. All rights reserved.

17 The Modern View of Atomic Structure
The atom contains: Electrons: constitute most of the atomic volume, responsible for the chemistry of the atom 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. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

18 The Mass and Change of the Electron, Proton, and Neutron
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

19 The Chemists’ Shorthand: Atomic Symbols
39 Mass number  K  Element Symbol 19 Atomic number  Copyright©2000 by Houghton Mifflin Company. All rights reserved.

20 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Chemical Bonds The forces that hold atoms together in compounds. Covalent bonds result from atoms sharing electrons. Molecule: a collection of covalently-bonded atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

21 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 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

22 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Ions Cation: A positive ion Mg2+, NH4+ Anion: A negative ion Cl, SO42 Ionic Bonding: Force of attraction between oppositely charged ions. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

23 Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Periodic Table Elements classified by: properties  atomic number Groups (vertical) 1A = alkali metals 2A = alkaline earth metals 7A = halogens 8A = noble gases Periods (horizontal) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

24 Naming Compounds Binary Ionic 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 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

25 Naming Compounds (continued)
Binary Ionic Compounds (Type II):  metal forms more than one cation  use Roman numeral in name PbCl2 Pb2+ is cation PbCl2 = lead (II) chloride Copyright©2000 by Houghton Mifflin Company. All rights reserved.

26 Naming Compounds (continued)
Binary compounds (Type III):  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 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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