Chapter 2. Chapter 2

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1 Chapter 2 Atoms, Molecules, and Ions Chapter 2 Atomic Theory Model for atom and ions that works well for chemistry Molecules Combinations of atoms Ways of representing molecules: formulas and models Names and formulas Binary molecular compounds Ionic compounds Acids Organic compounds Brief introduction 1

Atomic Theory Elements composed of small particles called atoms All atoms of a given element are identical What does experiment tell us about atoms?

2 Atomic Theory Elements composed of small particles called atoms All atoms of a given element are identical What does experiment tell us about atoms? Radioactivity Discovered in late 19 th century α-particles: positive (+2) and heavy Β-particles: negative (-1) and light γ-rays: energy (now know: He nuclei) (now know: electrons) (Incredible Hulk) Conclusion: atoms contain smaller particles 2

3 Rutherford s Experiment What does this experiment tell us about the atom? The Nuclear Atom Atoms contain a heavy core Called the nucleus of the atom 3

4 Atomic Structure Our model: Atoms made of three particles Electrons (e - ): light (1/2000 amu) negative (-1) Protons (p + ): heavy (1 amu) positive (+1) Neutrons (n o ): heavy (1 amu) neutral Atoms are electrically neutral What does this imply about # electrons and # protons? Imply anything about neutrons? Atomic and Mass Numbers Atomic Number (Z) : # protons in nucleus Characteristic of a given element Mass Number (A): #protons + # neutrons in nucleus Isotopes: atoms with same atomic number but different mass numbers ( A ZX) Carbon isotopes: 12 6 C 13 6 C 14 6 C Oxygen isotopes: 16 8 O 17 8 O 18 8 O 4

5 Ions Electrons can be added or removed from an atom or molecule. Electrons added: negative ion (anion) Electrons removed: positive ion (cation) Examples: Li ion (1 electron removed) 3 protons, 2 electrons +1 O ion (2 electrons added) 8 protons, 10 electrons -2 Molecules Two or more atoms held together by a chemical bond. Examples: H 2 O, NH 3, CH 4 Diatomic: two atoms in molecule (H 2 ) Polyatomic: three or more atoms in molecule (H 2 O, O 3 ) Chemical bond = shared electrons 5

Molecular Compounds Made of molecules Usually formed between two nonmetals Right side of periodic table (except for H) CO 2, BF 3, PCl 3, CH 4, H 2 O, XeF 4 Formulas for Molecules Molecular formula

6 Molecular Compounds Made of molecules Usually formed between two nonmetals Right side of periodic table (except for H) CO 2, BF 3, PCl 3, CH 4, H 2 O, XeF 4 Formulas for Molecules Molecular formula Shows exact number of atoms in molecule Simplest (empirical) formulas Shows simplest ratio of atoms in molecule Structural formulas Shows how atoms are bonded together Condensed structural and skeletal formulas Simplified structures in organic chemistry Molecular geometry Shows three dimensional structure (Chapter 10) Molecular models Help visualize three dimensional structure 6

7 Molecular Formula Shows actual number of atoms in molecule H 2 O C 2 H 4 (ethylene) C 27 H 46 O (cholesterol) O 2 O 3 (oxygen) (ozone) Above two are allotropes Two different forms of same element Simplest (Empirical) Formulas Simplest whole number ratio of atoms in molecule Example: Ethylene Molecular formula C 2 H 4 Simplest formula CH 2 Polymers Long chains Exact number atoms unknown Polyethylene (above): simplest formula = CH 2 7

8 Structural Formulas Show how atoms in molecule are bonded Condensed Structural Formulas Simplified structural formulas Use subscripts for multiple atoms bonded to same atom Subscripted atoms are bonded to element on left Organic: sometimes omit C-C bonds represents?? 8

9 Organic Chemistry Basic molecules: hydrocarbons (C, H) Few other elements involved: mainly O and N Regular bonding patterns for key elements H: 1 bond C: 4 bonds O: 2 bonds N: 3 bonds Skeletal Formulas Represent C atoms by angled junctions Use H atoms to give each C four bonds 9

10 Skeletal Formulas What are the skeletal formulas for the following: What are the condensed structural and molecular formula for this molecule? Skeletal Formulas Why do this? Organic molecules can be huge Carbon backbone frequently not as important as noncarbon atoms Skeletal structures are compact and give most important information Structure Functional groups (later in lecture) Cholesterol 10

Molecular Models Molecules are small and generally three-dimensiona Molecules seldom are flat! We frequently represent them with physical or computer models.

11 Molecular Models Molecules are small and generally three-dimensiona Molecules seldom are flat! We frequently represent them with physical or computer models. Structural formula Ball-and-stick Space-filling Molecular Models Computer models frequently generated using Experimental data (e.g., x-ray diffraction) Theoretical calculations Useful for visualizing three-dimensional structures Example: RasWin viewer (On USB drive) Ethanol Vitamin C 11

htm Ionic Compounds Ionic Compounds Made of positive and negative ions Charges must balance Model as a

12 Molecular Molecules Good example is model of DNA Difficult to visualize in two dimensions 3-D model more useful Ionic Compounds Ionic Compounds Made of positive and negative ions Charges must balance Model as a large stack of ions Ionic compounds usually formed between a metal and a nonmetal Opposite sides of periodic table NaCl, K 2 O, MgF 2 Can involve polyatomic ions 12

13 Polyatomic Ions Polyatomic ions: Ions that are made of two or more atoms Hydroxide: OH - Phosphate: PO 4 3- Ammonium: NH 4 + Table 2.3 in the text, p 61 You should know the name, formula, and charge of the ions Polyatomic Cations NH 4+, mercury (I) Hg 2 2+ Polyatomic Anions Polyatomic Ions CO 3 2-, HCO 3-, SO 4 2-, HSO 4-, PO 4 3-, HPO 4 2-, H 2 PO 4 - (carbonate, hydrogen carbonate, etc.) NO 3 - (nitrate), NO 2 - (nitrite), ClO 4 - (perchlorate), ClO 3 - (chlorate), ClO 2 - (chlorite) SO 3 2- (sulfite) CrO 4 2-, Cr 2 O 7 2-, MnO 4 - OH -, CN -, SCN -, O

14 Ionic Compounds Can involve polyatomic ions Na 2 CO 3 Hg 2 I 2 (NH 4 ) 3 PO 4 Names and Formulas Vocabulary of chemistry We deal with MANY compounds Need a standard method for representing them with names and formulas Will look at Binary molecular compounds Ionic compounds Introduce organic compounds 14

15 Naming: Binary Molecular Compounds First element: same name as element Second element: ide suffix Greek prefixes tell the number of atoms present (Table 2.4) 1: mono 4: tetra 7: hepta 2: di 5: penta 8: octa 3: tri 6: hexa 9: nona 10: deca Examples: CO -- carbon monoxide CO 2 -- carbon dioxide Naming: Binary Molecular Compounds Question: What are the names or formulas of these compounds? NO 2 Carbon tetrachloride P 2 O 5 15

Ionic Compounds Ionic compounds are arrays of positive and negative ions. Model of sodium chloride The formulas for ionic compounds always are simplest formulas.

16 Ionic Compounds Ionic compounds are arrays of positive and negative ions. Model of sodium chloride The formulas for ionic compounds always are simplest formulas. Simplest formula: simplest whole-number ratio of elements Sodium chloride: NaCl Formulas of Ionic Compounds Most of Table 2.3 in picture at right Compounds are electrically neutral Question: What is formula of a compound of sodium and oxygen? Question: What is formula of aluminum oxide? Question: What is formula of potassium phosphate? (PO 4 3- ) 16

17 Naming Ionic Compounds Cation Names If only one ion possible (Group 1A, IIA, Al): Cation name = element name Na + = sodium Ca 2+ = calcium More than one ion (transition metals): Use Stock notation Roman numeral for charge Cu + = copper(i) Cu 2+ = copper(ii) Naming Ionic Compounds Anion names Add ide to stem of element s name (Table 2.3 Chang) Cl - = chloride O 2- = oxide 17

18 Naming Ionic Compounds Question: What are the names or formulas of the following compounds? KCl calcium bromide FeCl 2 ammonium nitrate Co(MnO 4 ) 2 Lead (II) sulfate Potassium hydride Potassium ion always +1 Naming Step 1: Decide if compound is molecular or ionic Step 2: Use conventions we have discussed Examples Aluminum sulfate BF 3 K 2 O Carbon monoxide NaSCN 18

19 Naming Acids Binary Acids HCl (aq) hydrochloric acid HF (aq) hydrofluoric acid Oxoacids H 2 SO 4 sulfuric acid HNO 3 nitric acid HClO 3 chloric acid H 3 PO 4 phosphoric acid Naming Acids Often more than one oxoacid for a given element. Start with ic acid, such as chloric acid, HClO 3 One more O per... ic HClO 4 perchloric acid The ic acid is here HClO 3 chloric acid One less O... ous HClO 2 chlorous acid Two less O hypo... ous HClO hypochlorous acid Note: per and hypo acids don t always exist 19

20 Naming Oxoacid Anions ous acid ic acid anion =... ite anion = ate Examples: ClO - 3 Chlorate (HClO 3 = chloric acid) ClO - 2 Chlorite (HClO 2 = chlorous acid) ClO - Hypochlorite (HClO = hypochlorous acid) ClO - 4 Perchlorate (HClO4 = perchloric acid) Hydrates Specific number of water molecules attached Use Greek prefixes to specify number of waters CuSO 4 5H 2 O copper(ii) sulfate pentahydrate CuSO 4 5H 2 O CuSO 4 20

21 Organic Compounds This is an introduction. Naming organics can be complicated Alkanes: straight-chain hydrocarbons (C n H 2n+2 ) CH 4 methane C 2 H 6 ethane C 3 H 8 propane More in table 2.8 I will not cover hydrocarbon naming on the exam Functional Groups Give organic compounds their personality Know the functional groups below -OH alcohol -NH 2 amine organic base -COOH carboxyl organic acid Aldehyde Ketone 21

22 Functional Groups Acetic acid CH 3 COOH Methyl amine CH 3 NH 2 Alanine CH 3 CH(NH 2 )COOH (an amino acid) DNA DNA strands held together by interactions of functional groups Hydrogen bonding (Chpt 11) 22

23 Solubility Functional groups help us understand the solubility of organic compounds Compounds similar to water (H-O-H) tend to dissolve in water Contain OH or NH bonds Which of the following would you predict to be water-soluble? CH 3 CH 2 OH CH 3 CH 2 CH 3 Drug Metabolism Caffeine metabolism occurs in the liver. cytochrome P450 oxidase enzyme Adding NH groups makes compound more water soluble Excreted in urine 23

Ionic Compounds. And Acids

Ionic Compounds. And Acids CHAPTER 7 LANGUAGE OF CHEMISTRY CLASSIFICATION OF COMPOUNDS Inorganic compounds does not contain the element carbon, but there are exception to this rule, CO 2 (carbon dioxide), CO 3 2 (carbonate), and