ATOMS, MOLECULES, AND IONS

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ATOMS, MOLECULES, AND IONS

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ATOMS, MOLECULES, AND IONS Chapter Two: ATOMS, MOLECULES, AND IONS

Early History of Chemistry Greeks were the first to attempt to explain why chemical changes occur. Alchemy dominated for 2000 years: Several elements discovered Mineral acids prepared Robert Boyle was the first “chemist”: Performed quantitative experiments 2.1 Copyright © Houghton Mifflin Company. All rights reserved.

Three Important Laws Law of conservation of mass (Lavoisier): Mass is neither created nor destroyed Law of definite proportion (Proust): A given compound always contains exactly the same proportion of elements by mass 2.2 Copyright © Houghton Mifflin Company. All rights reserved.

Three Important Laws (continued) Law of multiple proportions (Dalton): 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 2.2 Copyright © Houghton Mifflin Company. All rights reserved.

Dalton’s Atomic Theory (1808) Each element is made up of tiny particles called atoms. 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Dalton’s Atomic Theory (continued) The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways. 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Dalton’s Atomic Theory (continued) Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms. 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Dalton’s Atomic Theory (continued) 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. 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Concept Check Which of the following statements regarding Dalton’s atomic theory are still believed to be true? Elements are made of tiny particles called atoms. All atoms of a given element are identical. A given compound always has the same relative numbers and types of atoms. IV. Atoms are indestructible. Statements I and III are true. Statement II is not true (due to isotopes and ions). Statement IV is not true (due to nuclear chemistry). Copyright © Houghton Mifflin Company. All rights reserved.

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! 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Gay-Lussac and Avogadro Gay-Lussac measured (under same conditions of T and P) the volumes of gases that reacted with each other. Avogadro’s Hypothesis: At the same T and P, equal volumes of different gases contain the same number of particles 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Representing Gay-Lussac’s Results 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Representing Gay-Lussac’s Results 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Representing Gay-Lussac’s Results 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Representing Gay-Lussac’s Results 2.3 Copyright © Houghton Mifflin Company. All rights reserved.

Early Experiments to Characterize the Atom J. J. Thomson (1898-1903): Postulated the existence of electrons using cathode-ray tubes Determined the charge-to-mass ratio of an electron The atom must also contain positive particles that balance exactly the negative charge carried by the electrons 2.4 Copyright © Houghton Mifflin Company. All rights reserved.

Cathode Ray Tube 2.4 Copyright © Houghton Mifflin Company. All rights reserved.

Early Experiments to Characterize the Atom Robert Millikan (1909): Performed experiments involving charged oil drops Determined the magnitude of the electron charge Calculated the mass of the electron 2.4 Copyright © Houghton Mifflin Company. All rights reserved.

Millikan Oil Drop Experiment 2.4 Copyright © Houghton Mifflin Company. All rights reserved.

Early Experiments to Characterize the Atom Ernest Rutherford (1911): Explained the nuclear atom Atom has a dense center of positive charge called the nucleus Electrons travel around the nucleus at a relatively large distance 2.4 Copyright © Houghton Mifflin Company. All rights reserved.

Rutherford’s Gold Foil Experiment 2.4 Copyright © Houghton Mifflin Company. All rights reserved.

The Modern View of Atomic Structure The atom contains: Electrons Protons – found in the nucleus; positive charge equal in magnitude to the electron’s negative charge Neutrons – found in the nucleus; no charge; virtually same mass as a proton 2.5 Copyright © Houghton Mifflin Company. All rights reserved.

The Modern View of Atomic Structure The nucleus is: Small compared with the overall size of the atom Extremely dense; accounts for almost all of the atom’s mass 2.5 Copyright © Houghton Mifflin Company. All rights reserved.

Nuclear Atom Viewed in Cross Section Copyright © Houghton Mifflin Company. All rights reserved.

The Modern View of Atomic Structure Isotopes: Atoms with the same number of protons but different numbers of neutrons Show almost identical chemical properties; chemistry of atom is due to its electrons In nature most elements contain mixtures of isotopes 2.5 Copyright © Houghton Mifflin Company. All rights reserved.

Two Isotopes of Sodium 2.5 Copyright © Houghton Mifflin Company. All rights reserved.

Exercise A certain isotope X+ contains 54 electrons and 78 neutrons. What is the mass number of this isotope? The mass number is 133. The plus charge in X+ means that the ion has lost an electron, therefore the number of protons is 55 (54+1). The ion is Cs+ with a mass number of 133 (55+78). Note: Use the red box animation to assist in explaining how to solve the problem. 2.5/2.6 Copyright © Houghton Mifflin Company. All rights reserved.

Chemical Bonds Covalent Bonds: Bonds form between atoms by sharing electrons Resulting collection of atoms is called a molecule 2.6 Copyright © Houghton Mifflin Company. All rights reserved.

Covalent Bonding 2.6 Copyright © Houghton Mifflin Company. All rights reserved.

Chemical Bonds Ionic Bonds: Bonds form due to force of attraction between oppositely charged ions Ion – atom or group of atoms that has a net positive or negative charge Cation – positive ion; lost electron(s) Anion – negative ion; gained electron(s) 2.6 Copyright © Houghton Mifflin Company. All rights reserved.

Molecular vs. Ionic Compounds 2.6 Copyright © Houghton Mifflin Company. All rights reserved.

The Periodic Table Metals vs. Nonmetals Groups or Families – elements in the same vertical columns Alkali metals, alkaline earth metals, halogens, and noble gases Periods – horizontal rows of elements 2.7 Copyright © Houghton Mifflin Company. All rights reserved.

The Periodic Table 2.7 Copyright © Houghton Mifflin Company. All rights reserved.

Naming Compounds Binary Compounds: Binary Ionic Compounds: Composed of two elements Ionic and covalent compounds included Binary Ionic Compounds: Metal-nonmetal Binary Covalent Compounds: Nonmetal to nonmetal 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Binary Ionic Compounds (Type I) Cation is always named first and the anion second. Monatomic cation has the same name as its parent element. Monatomic anion is named by taking the root of the element name and adding –ide. 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Binary Ionic Compounds (Type I) Examples: KCl Potassium chloride MgBr2 Magnesium bromide CaO Calcium oxide 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Binary Ionic Compounds (Type II) Metals in these compounds form more than one type of positive charge. Charge on the metal ion must be specified. Roman numeral indicates the charge of the metal cation. Transition metal cations usually require a Roman numeral. 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Binary Ionic Compounds (Type II) Examples: CuBr Copper(I) bromide FeS Iron(II) sulfide PbO2 Lead(IV) oxide 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Polyatomic Ions Must be memorized (see Table 2.5 on pg. 62 in text). Examples of compounds containing polyatomic ions: NaOH Sodium hydroxide Mg(NO3)2 Magnesium nitrate (NH4)2SO4 Ammonium sulfate 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Formation of Ionic Compounds 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Binary Covalent Compounds (Type III) Formed between two nonmetals. First element is named first, using the full element name. Second element is named as if it were an anion. Prefixes are used to denote the numbers of atoms present. Prefix mono- is never used for naming the first element. 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Binary Covalent Compounds (Type III) Examples: CO2 Carbon dioxide SF6 Sulfur hexafluoride N2O4 Dinitrogen tetroxide 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Overall Strategy for Naming Chemical Compounds Copyright © Houghton Mifflin Company. All rights reserved.

Flowchart for Naming Binary Compounds Copyright © Houghton Mifflin Company. All rights reserved.

Acids Acids can be recognized by the hydrogen that appears first in the formula—HCl. Molecule with one or more H+ ions attached to an anion. 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Acids If the anion does not contain oxygen, the acid is named with the prefix hydro- and the suffix -ic. Examples: HCl Hydrochloric acid HCN Hydrocyanic acid H2S Hydrosulfuric acid 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Acids If the anion does contain oxygen: Examples: HNO3 Nitric acid The suffix -ic is added to the root name if the anion name ends in -ate. Examples: HNO3 Nitric acid H2SO4 Sulfuric acid HC2H3O2 Acetic acid 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Acids If the anion does contain oxygen: Examples: HNO2 Nitrous acid The suffix -ous is added to the root name if the anion name ends in -ite. Examples: HNO2 Nitrous acid H2SO3 Sulfurous acid HClO2 Chlorous acid 2.8 Copyright © Houghton Mifflin Company. All rights reserved.

Flowchart for Naming Acids Copyright © Houghton Mifflin Company. All rights reserved.

Exercise Which of the following compounds is named incorrectly? KNO3 potassium nitrate TiO2 titanium(II) peroxide Sn(OH)4 tin(IV) hydroxide PBr5 phosphorus pentabromide CaCrO4 calcium chromate The correct answer is “b”. The charge on oxygen is -2. Since there are two oxygen atoms, the overall charge is -4. Therefore, the charge on titanium must be +4 (not +2 as the Roman numeral indicates). 2.8 Copyright © Houghton Mifflin Company. All rights reserved.