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Atoms, Molecules, and Ions Chapter 2 Atoms, Molecules, and Ions.

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Presentation on theme: "Atoms, Molecules, and Ions Chapter 2 Atoms, Molecules, and Ions."— Presentation transcript:

1 Atoms, Molecules, and Ions Chapter 2 Atoms, Molecules, and Ions

2 Atoms, Molecules, and Ions Historical Discovery of Atom Democritus – Laughing Philosopher © 2009, Prentice-Hall, Inc. John Dalton – solid sphere, combine Thomson – Plum Pudding Model Rutherford – Gold Foil Experiment Millikan – Oil Drop Experiment Bohr – Orbital Model Chadwick – Neutrons Wave Mechanical Model

3 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc.

4 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton. 4 Postulate Theory

5 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Dalton's Postulates 1. Each element is composed of extremely small particles called atoms.

6 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Dalton's Postulates 2. All atoms of a given element are identical in mass and properties, but the atoms of one element are different from the atoms of another element.

7 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Dalton's Postulates 3. Atoms of an element are not changed by chemical reactions; atoms are neither created nor destroyed in chemical reactions – just REARRANGED. Supports the Law of Conservation of Mass

8 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Dalton’s Postulates 4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. Supports the Law of Constant Composition

9 Atoms, Molecules, and Ions Law of Constant Composition Joseph Proust (1754–1826) also known as the law of definite proportions states that the elemental composition of a pure substance never varies.

10 Atoms, Molecules, and Ions Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place.

11 Atoms, Molecules, and Ions Subatomic Particles Landmark Discoveries lead to the current model of atomic theory

12 Atoms, Molecules, and Ions Streams of negatively charged particles were found to emanate from cathode (- electrode) tubes. J. J. Thompson is credited with their discovery (1897). The Busy Electron

13 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. The Busy Electron Thompson measured the charge/mass ratio of the electron to be 1.76  10 8 coulombs/g. Electron Charge (C) = 1.76  10 8 coulombs Electron Mass (g) 1 gram

14 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Millikan Oil Drop Experiment He examined the relationship between voltage of plates affected rate of electron fall. Open text to pg. 40 Fig. 2.5 Explanation

15 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Millikan Oil Drop Experiment Robert Millikan (University of Chicago) determined the charge on the electron in Charge of Electron = 9.10 x g

16 Atoms, Molecules, and Ions Subatomic Particles Relative Mass and Charge © 2009, Prentice-Hall, Inc.

17 Atoms, Molecules, and Ions Relative Mass Image © 2009, Prentice-Hall, Inc.

18 Atoms, Molecules, and Ions Radioactivity Radioactivity is the spontaneous emission of radiation by an atom. It was first observed by Henri Becquerel Followed by Marie and Pierre Curie. Shared 1903 Nobel Prize in Physics

19 Atoms, Molecules, and Ions Radioactivity Three types were discovered by Rutherford: –  particles, Alpha, bent by electric field, +2 charge –  particles, Beta, bent by electric field, - 1 charge –  rays, Gamma, unaffected by electric field, no charge

20 Atoms, Molecules, and Ions The Atom, circa 1900 The prevailing theory was that of the “plum pudding” model, put forward by Thompson. It featured a positive sphere of matter with negative electrons imbedded in it.

21 Atoms, Molecules, and Ions Discovery of the Nucleus Ernest Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. Particles were deflected by foil.

22 Atoms, Molecules, and Ions The Nuclear Atom Since some particles were deflected at large angles, Thompson’s model could not be correct. Rutherford proposed the positive nucleus containing protons.

23 Atoms, Molecules, and Ions The Nuclear Atom Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom. Most of the volume of the atom is empty space.

24 Atoms, Molecules, and Ions Other Subatomic Particles Protons discovered by Rutherford, Neutrons discovered by James Chadwick,1932.

25 Atoms, Molecules, and Ions Subatomic Particles Protons and electrons are have a charge. Protons and neutrons have essentially the same mass. The mass of an electron is so small we ignore it.

26 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Symbols of Elements Nuclear Symbol Hyphen Notation C -12

27 Atoms, Molecules, and Ions Atomic Number Atoms of the same element have the same number of protons: the atomic number (Z)

28 Atoms, Molecules, and Ions Atomic Mass The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

29 Atoms, Molecules, and Ions Isotopes Isotopes are atoms have different masses. Isotopes have different numbers of neutrons C 12 6 C 13 6 C 14 6 C

30 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Atomic Mass Atomic and molecular masses can be measured with great accuracy with a mass spectrometer. Turn to pg. 48 in text

31 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Average Atomic Mass Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. Average mass is calculated from the isotopes of an element weighted by their relative abundances.

32 Atoms, Molecules, and Ions Calculating Average Atomic Mass EX. You have a box containing two sizes of marbles. 25% of the marbles have a mass of 2.0 g. 75% of the marbles have a mass of 3.0 g. Calculate the average weight of the marble.

33 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. EX. Copper has two naturally occurring isotopes: Cu-63 (69.17% abundant) with amu = Cu-65 (30.83% abundant) with amu = Calculate the average atomic mass.

34 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Periodic Table It is a systematic catalog of the elements. Elements are arranged in order of atomic number.

35 Atoms, Molecules, and Ions Periodicity or Periodic Law Notices a repeating pattern of reactivities! Function of the atomic number called periodicity.

36 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Periodic Table The rows on the periodic chart are periods. Columns are groups or families. Elements in the same group have similar chemical properties.

37 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Groups These five groups are known by their names.

38 Atoms, Molecules, and Ions

39 Atoms, Molecules, and Ions Periodic Table Nonmetals are on the right side of the periodic table (with the exception of H).

40 Atoms, Molecules, and Ions Periodic Table Metalloids border the stair-step line (with the exception of Al and Po).

41 Atoms, Molecules, and Ions Periodic Table Metals are on the left side of the chart. 80% of elements are metals.

42 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. Naming and Writing Inorganics

43 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Chemical Formulas Molecular compounds are composed of molecules and almost always contain only nonmetals. - covalent compounds - NM + NM

44 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Diatomic Molecules These seven elements occur naturally as molecules containing two atoms. Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2

45 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Types of Formulas Empirical formulas give the lowest whole- number ratio of atoms of each element in a compound. Molecular formulas give the exact number of atoms of each element in a compound.

46 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Types of Formulas Structural formulas show the order in which atoms are bonded. Perspective drawings show the three-dimensional array of atoms in a compound. Ball+Stick models show the atoms as spheres and bonds as sticks. Space filling model shows relative sizes of atoms.

47 Atoms, Molecules, and Ions Ions When atoms lose or gain electrons, they become ions. –Ca+ions are positive, formed as atoms lose e-, metals –Anions are negative, formed as atoms gain e-, nonmetals

48 Atoms, Molecules, and Ions Ionic Bonds Ionic compounds = Metal + Nonmetal Ionic compounds = cation + anion

49 Atoms, Molecules, and Ions Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: –The charge on the cation becomes the subscript on the anion. –The charge on the anion becomes the subscript on the cation. –If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.

50 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. RIP Kris KrossKris Kross

51 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Writing Chemical Formulas Assign Charges then criss x cross the numbers DO NOT criss x cross the charges, just the #s Ex. Magnesium Chloride Assign ChargesMg +2 Cl -1 Criss-Cross MgCl 2 Chemical Formula MgCl 2

52 Atoms, Molecules, and Ions Common Cations Pg. 62 or on back fold of text

53 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Common Anions Pg. 64 or on back fold of text

54 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Inorganic Nomenclature Write the name of the metal cation. If the metal cation can have more than one charge, write the charge as a Roman Numeral in parentheses. (CLIMT) If the anion is an element, change its ending to -ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion.

55 Atoms, Molecules, and Ions Patterns in Oxyanion Nomenclature When there are two oxyanions involving the same element: –The one with fewer oxygens ends in -ite. NO 2 − : nitrite ; SO 3 2− : sulfite –The one with more oxygens ends in -ate. NO 3 − : nitrate; SO 4 2− : sulfate -ate is GREAT and –ite is LIGHT

56 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Patterns in Oxyanion Nomenclature The one with the second fewest oxygens ends in -ite. –ClO 2 − : chlorite The one with the second most oxygens ends in -ate. –ClO 3 − : chlorate

57 Atoms, Molecules, and Ions Patterns in Oxyanion Nomenclature The one with the fewest oxygens has the prefix hypo- and ends in -ite. –ClO − : hypochlorite The one with the most oxygens has the prefix per- and ends in -ate. –ClO 4 − : perchlorate

58 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Acid Nomenclature If the anion in the acid ends in -ide, change the ending to -ic acid and add the prefix hydro- HCl: hydrochloric acid HBr: hydrobromic acid HI: hydroiodic acid

59 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Acid Nomenclature If the anion in the acid ends in -ate, change the ending to -ic acid. HClO 3 : chloric acid HClO 4 : perchloric acid

60 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Acid Nomenclature If the anion in the acid ends in -ite, change the ending to -ous acid. HClO: hypochlorous acid HClO 2 : chlorous acid

61 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Molecular Nomenclature The less electronegative atom is usually listed first. A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however).

62 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. The ending on the more electronegative element is changed to -ide. –CO 2 : carbon dioxide –CCl 4 : carbon tetrachloride Molecular Nomenclature

63 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one. N 2 O 5 : dinitrogen pentoxide Molecular Nomenclature

64 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Nomenclature of Organic Compounds Organic chemistry is the study of carbon. Organic chemistry has its own system of nomenclature.

65 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Nomenclature of Organic Compounds The simplest hydrocarbons (compounds containing only carbon and hydrogen) are alkanes.

66 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Nomenclature of Organic Compounds The first part of the names above correspond to the number of carbons (meth- = 1, eth- = 2, prop- = 3, etc.).

67 Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Nomenclature of Organic Compounds When a hydrogen in an alkane is replaced with something else (a functional group, like -OH in the compounds above), the name is derived from the name of the alkane. The ending denotes the type of compound. –An alcohol ends in -ol.


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