Chapter 2 Atoms, Molecules and Ions

Transcription

1 Sec$on 2.1 The Early History of Chemistry Chapter 2 Atoms, Molecules and Ions

2 Sec$on 2.1 The Early History of Chemistry Early History of Chemistry Greeks were the first to a?empt to explain why chemical changes occur. Alchemy dominated for 2000 years. Several elements discovered. Mineral acids prepared. Robert Boyle was the first chemist. Performed quan$ta$ve experiments. Developed first experimental defini$on of an element. Copyright Cengage Learning. All rights reserved 2

3 Sec$on 2.2 Fundamental Chemical Laws Three Important Laws Law of conserva$on of mass (Lavoisier): Mass is neither created nor destroyed in a chemical reac$on. Law of definite propor$on (Proust): A given compound always contains exactly the same propor$on of elements by mass. Copyright Cengage Learning. All rights reserved 3

4 Sec$on 2.2 Fundamental Chemical Laws Three Important Laws (con$nued) Law of mul$ple propor$ons (Dalton): When two elements form a series of compounds, the ra$os of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. Copyright Cengage Learning. All rights reserved 4

5 Sec$on 2.3 Dalton s Atomic Theory Dalton s Atomic Theory (1808) Each element is made up of =ny par=cles called atoms. Copyright Cengage Learning. All rights reserved 5

6 Sec$on 2.3 Dalton s Atomic Theory Dalton s Atomic Theory (con$nued) The atoms of a given element are iden=cal; the atoms of different elements are different in some fundamental way or ways. Copyright Cengage Learning. All rights reserved 6

7 Sec$on 2.3 Dalton s Atomic Theory Dalton s Atomic Theory (con$nued) Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same rela$ve numbers and types of atoms. Copyright Cengage Learning. All rights reserved 7

8 Sec$on 2.3 Dalton s Atomic Theory Dalton s Atomic Theory (con$nued) Chemical reac=ons involve reorganiza=on of the atoms changes in the way they are bound together. The atoms themselves are not changed in a chemical reac$on. Copyright Cengage Learning. All rights reserved 8

9 Sec$on 2.4 Early Experiments to Characterize the Atom J. J. Thomson ( ) Postulated the existence of nega$vely charged par$cles, that we now call electrons, using cathode-ray tubes. Determined the charge-to-mass ra$o of an electron. The atom must also contain posi$ve par$cles that balance exactly the nega$ve charge carried by electrons. Copyright Cengage Learning. All rights reserved

10 Sec$on 2.4 Early Experiments to Characterize the Atom Cathode-Ray Tube Copyright Cengage Learning. All rights reserved

11 Sec$on 2.4 Early Experiments to Characterize the Atom Robert Millikan (1909) Performed experiments involving charged oil drops. Determined the magnitude of the charge on a single electron (e - charge = x C). Calculated the mass of the electron ( kg). Copyright Cengage Learning. All rights reserved

12 Sec$on 2.4 Early Millikan Experiments Oil Drop Experiment to Characterize the Atom Copyright Cengage Learning. All rights reserved

13 Sec$on 2.4 Early Experiments to Characterize the Atom Henri Becquerel (1896) Discovered radioac$vity by observing the spontaneous emission of radia$on by uranium. Three types of radioac$ve emission exist: Gamma rays (ϒ) high energy light Beta par$cles (β) a high speed electron Alpha par$cles (α) a par$cle with a 2+ charge Copyright Cengage Learning. All rights reserved

14 Sec$on 2.4 Early Experiments to Characterize the Atom Ernest Rutherford (1911) Explained the nuclear atom. The atom has a dense center of posi$ve charge called the nucleus. Electrons travel around the nucleus at a large distance rela$ve to the nucleus. Copyright Cengage Learning. All rights reserved

15 Sec$on 2.4 Early Rutherford s Experiments Experimental to Characterize Design the Atom Copyright Cengage Learning. All rights reserved

16 Sec$on 2.5 The Modern The atom View contains: of Atomic Structure: An Introduc=on Electrons found outside the nucleus; nega$vely charged. Protons found in the nucleus; posi$ve charge equal in magnitude to the electron s nega$ve charge. Neutrons found in the nucleus; no charge; virtually same mass as a proton.

17 Sec$on 2.5 The Modern The nucleus View is: of Atomic Structure: An Introduc=on Small compared with the overall size of the atom. Extremely dense; accounts for almost all of the atom s mass. Copyright Cengage Learning. All rights reserved 17

18 Sec$on 2.5 The Modern View of Atomic Structure: An Introduc=on Isotopes Atoms with the same number of protons but different numbers of neutrons. Show almost iden$cal chemical proper$es; chemistry of atom is due to its electrons. In nature most elements contain mixtures of isotopes. Copyright Cengage Learning. All rights reserved 18

19 Sec$on 2.5 The Modern View of Atomic Structure: An Introduc=on Two Isotopes of Sodium Copyright Cengage Learning. All rights reserved

20 Sec$on 2.5 The Modern View of Atomic Structure: An Introduc=on Isotopes are iden$fied by: Atomic Number (Z) number of protons Mass Number (A) number of protons plus number of neutrons Copyright Cengage Learning. All rights reserved 20

21 Sec$on 2.6 Molecules and Ions Atomic Weight Because in the real world we use large amounts of atoms and molecules, we use average masses in calcula$ons. An average mass is found using all isotopes of an element weighted by their rela$ve abundances. This is the element s atomic weight. That is: Atomic Weight = Ʃ [(isotope mass) (frac$onal natural abundance)] Note: the sum is for ALL isotopes of an element Copyright Cengage Learning. All rights reserved 21

22 Sec$on 2.6 Molecules and Ions 12 C is the standard for atomic mass, with a mass of exactly 12 atomic mass units (amu). The masses of all other atoms are given rela$ve to this standard. Elements occur in nature as mixtures of isotopes. Carbon = 98.89% 12 C 1.11% 13 C < 0.01% 14 C Copyright Cengage Learning. All rights reserved 22

23 Sec$on 2.6 Molecules and Ions Atomic Weight for Carbon 98.89% of 12 amu % of amu = exact number (0.9889)(12 amu) + (0.0111)( amu) = amu Copyright Cengage Learning. All rights reserved 23

24 Sec$on 2.6 Molecules and Ions Atomic Weight for Carbon Even though natural carbon does not contain a single atom with mass 12.01, for stoichiometric purposes, we can consider carbon to be composed of only one type of atom with a mass of This enables us to count atoms of natural carbon by weighing a sample of carbon. Copyright Cengage Learning. All rights reserved 24

25 Sec$on 2.6 Molecules and Ions Chemical Bonds Covalent Bonds Bonds form between atoms by sharing electrons. Resul$ng collec$on of atoms is called a molecule or molecular compound. Copyright Cengage Learning. All rights reserved 25

26 Sec$on 2.6 Molecules and Ions Chemical Bonds Ionic Bonds Bonds form due to force of a?rac$on between oppositely charged ions. Ion atom or group of atoms that has a net posi$ve or nega$ve charge. Ca=on posi$ve ion; lost electron(s). Anion nega$ve ion; gained electron(s). Copyright Cengage Learning. All rights reserved 26

27 Sec$on 2.6 Molecules Molecular and Compounds Ions (covalent) Copyright Cengage Learning. All rights reserved 27

28 Sec$on 2.6 Molecules and Ions Ionic Compounds The ionic compound NaCl Copyright Cengage Learning. All rights reserved 28

29 Sec$on 2.7 An Introduc=on to the Periodic Table The Periodic Table Metals vs. Nonmetals Groups or Families elements in the same ver$cal columns; have similar chemical proper$es Periods horizontal rows of elements Copyright Cengage Learning. All rights reserved 29

30 Sec$on 2.7 An The Introduc=on Periodic Table to the Periodic Table

31 Sec$on 2.7 An Introduc=on to the Periodic Table Groups or Families Table of common charges formed when crea$ng ionic compounds. Group or Family Charge Alkali Metals (1A) 1+ Alkaline Earth Metals (2A) 2+ Halogens (7A) 1 Noble Gases (8A) 0 Copyright Cengage Learning. All rights reserved 31

32 Sec$on 2.7 An Ions Introduc=on to the Periodic Table When an atom of a group of atoms loses or gains electrons, it becomes an ion. Ca/ons are formed when at least one electron is lost. Monatomic ca$ons are formed by metals. Anions are formed when at least one electron is gained. Monatomic anions are formed by nonmetals. Copyright Cengage Learning. All rights reserved 32

33 Sec$on 2.8 Naming Simple Compounds Naming Compounds Binary Compounds Composed of two elements Ionic and covalent compounds included Binary Ionic Compounds Metal nonmetal Binary Covalent Compounds Nonmetal nonmetal Copyright Cengage Learning. All rights reserved 33

34 Sec$on 2.8 Naming Simple Compounds Binary Ionic Compounds (Type I) 1. The ca$on is always named first and the anion second. 2. A monatomic ca$on takes its name from the name of the parent element. 3. A monatomic anion is named by taking the root of the element name and adding ide. Copyright Cengage Learning. All rights reserved 34

35 Sec$on 2.8 Naming Simple Compounds Binary Ionic Compounds (Type I) Examples: KCl Potassium chloride MgBr 2 Magnesium bromide CaO Calcium oxide Copyright Cengage Learning. All rights reserved 35

36 Sec$on 2.8 Naming Simple Compounds Binary Ionic Compounds (Type II) Metals in these compounds form more than one type of posi$ve ion. Charge on the metal ion must be specified. Roman numeral indicates the charge of the metal ca$on. Transi$on metal ca$ons usually require a Roman numeral. Elements that form only one ca$on do not need to be iden$fied by a roman numeral. Copyright Cengage Learning. All rights reserved 36

37 Sec$on 2.8 Naming Simple Compounds Binary Ionic Compounds (Type II) Examples: CuBr Copper(I) bromide FeS Iron(II) sulfide PbO 2 Lead(IV) oxide Copyright Cengage Learning. All rights reserved 37

38 Sec$on 2.8 Naming Simple Compounds Polyatomic Ions Must be memorized (see Table 2.5 on pg. 65 in text). Examples of compounds containing polyatomic ions: NaOH Sodium hydroxide Mg(NO 3 ) 2 Magnesium nitrate (NH 4 ) 2 SO 4 Ammonium sulfate Copyright Cengage Learning. All rights reserved 38

39 Sec$on 2.8 Naming Simple Compounds

40 Sec$on 2.8 Naming Simple Compounds Binary Covalent Compounds (Type III) Formed between two nonmetals. 1. The first element in the formula is named first, using the full element name. 2. The second element is named as if it were an anion. 3. Prefixes are used to denote the numbers of atoms present. 4. The prefix mono- is never used for naming the first element. Copyright Cengage Learning. All rights reserved 40

41 Sec$on 2.8 Naming Simple Compounds Prefixes Used to Indicate Number in Chemical Names Copyright Cengage Learning. All rights reserved 41

42 Sec$on 2.8 Naming Simple Compounds Binary Covalent Compounds (Type III) Examples: CO 2 Carbon dioxide SF 6 Sulfur hexafluoride N 2 O 4 Dinitrogen tetroxide Copyright Cengage Learning. All rights reserved 42

43 Sec$on 2.8 Naming Flowchart Simple for Naming Compounds Binary Compounds Copyright Cengage Learning. All rights reserved 43

44 Sec$on 2.8 Naming Overall Simple Strategy Compounds for Naming Chemical Compounds Copyright Cengage Learning. All rights reserved 44

45 Sec$on 2.8 Naming Simple Compounds Acids Acids can be recognized by the hydrogen that appears first in the formula HCl. Molecule with one or more H + ions a?ached to an anion. Copyright Cengage Learning. All rights reserved 45

46 Sec$on 2.8 Naming Simple Compounds 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 H 2 S Hydrosulfuric acid Copyright Cengage Learning. All rights reserved 46

47 Sec$on 2.8 Naming Simple Compounds Acids If the anion does contain oxygen: The suffix ic is added to the root name if the anion name ends in ate. Examples: HNO 3 Nitric acid H 2 SO 4 Sulfuric acid HC 2 H 3 O 2 Ace$c acid Copyright Cengage Learning. All rights reserved 47

48 Sec$on 2.8 Naming Simple Compounds Acids If the anion does contain oxygen: The suffix ous is added to the root name if the anion name ends in ite. Examples: HNO 2 Nitrous acid H 2 SO 3 Sulfurous acid HClO 2 Chlorous acid Copyright Cengage Learning. All rights reserved 48

49 Sec$on 2.8 Naming Flowchart Simple for Naming Compounds Acids Copyright Cengage Learning. All rights reserved