Atoms, Molecules and Ions Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. 2.All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements. 3.Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction. 4.A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction. 2.1

2 Dalton’s Atomic Theory

8 X 2 Y 16 X8 Y + 2.1

J.J. Thomson measured the mass to charge ratio of the electron. (1906 Nobel Prize in Physics) 2.2

Cathode Ray Tube 2.2

Cathode Ray Tube

e – charge = –1.60 x 10 –19 C Thomson’s charge/mass of e – = –1.76 x 10 8 C/g e – mass = 9.10 x 10 –28 g Measured mass of e - (1923 Nobel Prize in Physics) 2.2 An X-ray beam dislodges an electron from air molecules which becomes attached to an oil droplet.

(Uranium compound) 2.2

1.atoms positive charge is concentrated in the nucleus 2.proton (p) has opposite (+) charge of electron (-) 3.mass of p is 1840 x mass of e - (1.67 x g)  particle velocity ~ 1.4 x 10 7 m/s (~5% speed of light) (1908 Nobel Prize in Chemistry) 2.2

Rutherford’s Gold Foil Experiment

atomic radius ~ 100 pm = 1 x 10 –10 m nuclear radius ~ 5 x 10 –3 pm = 5 x 10 –15 m Rutherford’s Model of the Atom 2.2 “If the atom is the Houston Astrodome, then the nucleus is a marble on the 50-yard line.”

Chadwick’s Experiment (1932) (1935 Noble Prize in Physics for discovery of neutron) H atom has 1 p; He atom has 2 p mass He/mass H should = 2 measured mass He/mass H = 4  + 9 Be 1 n + 12 C + energy neutron (n) is neutral (charge = 0) n mass ~ p mass = 1.67 x 10 –24 g 2.2

mass p ~ mass n = 1840 x mass e – 2.2

Atomic number (Z) = number of protons in the nucleus. Mass number (A) = number of protons + number of neutrons. Isotopes are atoms of the same element (same number of protons) but different numbers of neutrons in their nuclei. X A Z C 12 6 C 13 6 C 14 6 U U Mass Number Atomic Number Element Symbol 2.3 Atomic number, Mass number and Isotopes

2.3 The Isotopes of Hydrogen ProtiumDeuterium Tritium (radioactive)

6 protons, 14 – 6 = 8 neutrons, 6 electrons 6 protons, 11 – 6 = 5 neutrons, 6 electrons Do You Understand Isotopes? 2.3 How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ?

Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal 2.4

A molecule is an aggregate of two or more atoms in a definite arrangement held together by covalent bonds. H2H2 H2OH2ONH 3 CH 4 A diatomic molecule contains only two atoms H 2, N 2, O 2, Br 2, HCl, CO A polyatomic molecule contains more than two atoms O 3, H 2 O, NH 3, CH 4 2.5

An ion is an atom, or group of atoms, that has a net positive or negative charge. Cation: ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. Anion: ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5

A monatomic ion contains only one atom. A polyatomic ion contains more than one atom. 2.5 Na +, Cl –, Ca 2+, O 2–, Al 3+, N 3– OH –, CN –, NH 4 +, NO 3 –

13 protons, 13 – 3 = 10 electrons 34 protons, = 36 electrons Do You Understand Ions? 2.5 How many protons and electrons are in ?Al How many protons and electrons are in ?Se –

2.5 Common Monatomic Cations

2.6

A molecular formula shows the exact number of atoms of each element in a molecule of the substance. An empirical formula shows the simplest whole-number ratio of the atoms in a substance. H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2 2.6

ionic compounds consist of a combination of cations and anions. the formula is always the same as the empirical formula the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl. Na + to Cl – ratio = 1 to 1 2.6

Formula of Ionic Compounds Al 2 O x +3 = +63 x –2 = –6 Al 3+ O 2– CaBr 2 1 x +2 = +22 x –1 = –2 Ca 2+ Br – Na 2 CO 3 2 x +1 = +21 x –2 = –2 Na + CO 3 2–

2.7 Monatomic negative ion names end in “ide.”

2.7

Chemical Nomenclature Ionic Compounds often a metal + nonmetal BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate 2.7

Transition metal ionic compounds Indicate the charge on the metal with Roman numerals (the Stock naming system). Common names use the “ic” and “ous” endings. FeCl 2 2 Cl – = –2 so Fe is +2 iron(II) chloride (ferrous chloride) FeCl 3 3 Cl – = –3 so Fe is +3 iron(III) chloride (ferric chloride) Cr 2 S 3 3 S –2 = –6 so Cr is +3chromium(III) sulfide 2.7

Molecular compounds Made of nonmetals or nonmetals + metalloids. Use common names for these: H 2 O, NH 3, CH 4 The element further left in periodic table is first. The element closest to bottom of group is first. If more than one compound can be formed from the same elements, use the prefixes to indicate the number of each kind of atom to specify the compound. The last element ends in “ide.” 2.7

HIhydrogen iodide NF 3 nitrogen trifluoride SO 2 sulfur dioxide N 2 Cl 4 dinitrogen tetrachloride NO 2 nitrogen dioxide N2ON2Odinitrogen monoxide Molecular Compounds 2.7 (Laughing Gas)

An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. Pure substance, hydrogen chloride, HCl (g). Dissolve in water yields H + and Cl – ions, hydrochloric acid, HCl (aq). An oxoacid is an acid that contains hydrogen, oxygen, and another element. HNO 3 nitric acid H 2 SO 4 sulfuric acid 2.7 HNO 3 HNO 2 nitrous acid H 2 SO 3 sulfurous acid H 2 CO 3 carbonic acid

2.7

A base can be defined as a substance that yields hydroxide ions (OH – ) when dissolved in water. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide 2.7

Hydrates are compounds that have a specific number of water molecules attached to them. BaCl 2 2H 2 O 2.7 LiClH 2 O MgSO 4 7H 2 O Sr(NO 3 ) 2 4H 2 O barium chloride dihydrate lithium chloride monohydrate magnesium sulfate heptahydrate strontium nitrate tetrahydrate CuSO 4 5H 2 O CuSO 4

Organic chemistry is the branch of chemistry that deals with carbon compounds C H H H OH C H H H NH 2 C H H H COH O methanolmethylamineacetic acid 2.7 Functional Groups