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Chapter 2: Atoms, Ions and Compounds

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1 Chapter 2: Atoms, Ions and Compounds
Problems: , , ,

2 Chapter 2 – Atoms, Ions and Compounds
2.1 The Rutherford Model of Atomic Structure (or Nuclear Model) Joseph John (J. J.) Thomson (1897) carried out experiments with cathode rays. His research group determined the charge-to-mass ratio of the particles in the rays. They determined the particles were composed of tiny, negatively charged subatomic particles  electrons (e–)

3 Atomic Structure Eugen Goldstein (late 1880s)
Discovered canal (or anode) rays which were composed of positively charged subatomic particles  protons (p+) And decades later, James Chadwick won the Nobel Prize winner for his discovery (1935)  neutron (n) = neutral subatomic particle

4 Plum-Pudding Model of the Atom
Thomson proposed that the atom was a uniform sphere of positively charged matter in which electrons were embedded electrons are like raisins in a pudding of protons

5 The Nuclear Atom: Protons and the Nucleus
Ernest Rutherford was a scientist who did many pioneering experiments in radioactivity He had members of his research group test Thomson’s Plum-Pudding Model using radioactive alpha (α) particles, basically helium atoms with a +2 charge and much bigger than an electron.

6 Rutherford's Alpha-Scattering Experiment
Alpha (α) particles shot at a thin gold foil that’s only a few atoms thick A circular detector is set up around the foil to determine what happens to the α particles. If Plum-pudding Model was correct, the α particles should go through the foil like bullets through tissue paper.

7 Rutherford's Alpha-Scattering Experiment
Experimental results: Most of the a particles went straight through, but some were deflected or even bounced back!

8 Rutherford's Alpha-Scattering Experiment
Consider what the scientists expected to observe given each model.

9 Rutherford's Alpha-Scattering Experiment
Rutherford’s interpretation of the results Most alpha (α) particles pass through foil Atom is mostly empty space with electrons moving around the space Some α are deflected or bounce back Atom must also contain a dense region, and particles hitting this region are deflected or bounce back towards source. Dense region = atomic nucleus (contains atom’s protons and neutrons) That’s why this is called the NUCLEAR Model of the Atom

10 Rutherford's Alpha-Scattering Experiment
Rutherford also estimated the size of the atom and its nucleus: An atom is 100,000 times (105 or 5 orders of magnitude) bigger than its nucleus.

11 Example 1 An atom is 100,000 times (105 or 5 orders of magnitude) bigger than its nucleus. If a nucleus = size of a small marble (~1 cm in diameter), indicate the length in meters then identify a common item that corresponds to that size for the following: a. 10 times bigger = _____________ m = ________________________ b. 100 times bigger = _____________ m = _______________________ c times bigger = _____________ m = ______________________ d. 10,000 times bigger = ____________ m = _____________________ e. 100,000 times bigger = ____________ m = ____________________

12 Properties of Protons, Neutrons, and Electrons
Subatomic Particle Charge Location Mass (amu) Proton +1 inside nucleus Neutron Electron -1 outside nucleus

13 2.2 Isotopes Each element always has the same number of protons, but the number of neutrons may vary. Atoms with different numbers of neutrons are called isotopes. Carbon exists as carbon-12, carbon-13, and carbon-14 where each carbon atom has 6 protons but 6, 7, or 8 neutrons respectively Isotopes are identified with an element name followed by the mass number Examples: uranium-235 (U-235), carbon-12 (C-12), cobalt-60 (Co-60), etc.

14 Atomic Notation shorthand for keeping track of number of protons and neutrons in the nucleus atomic number (Z): whole number of p+ = number of e– in neutral atom mass number (A): whole number sum of protons and neutrons in an atom Note: electrons contribute almost no mass to an atom E A Z element symbol mass number atomic number

15 Example Problem Complete the following table: Isotope Mass number
# of protons # of neutrons # of electrons strontium-86 92Mo zinc-72 136Ba2+ 31P3-

16 2.4 The Periodic Table of the Elements
Know which elements are metals, semimetals, nonmetals using the Periodic Table.

17 Properties of Non-Metals
dull appearance brittle non-conductor Examples: carbon (graphite in pencils), sulfur Properties of Metals conduct heat & electricity malleable: can be flattened into thin sheets ductile: can be stretched into a wire Examples: aluminum, copper, gold Properties of Metalloids (or Semimetals) Have properties of metals and nonmetals For example, silicon is shiny like a metal and acts as a semiconductor.

18 SOLIDS, LIQUIDS, AND GASES: KNOW the physical state of each element at 25C!
At standard state conditions (25C and 1 atm): Only mercury (Hg) and bromine (Br) are liquid H, N, O, F, Cl, and all Noble gases (group VIIIA) are gases All other elements are solids

19 2.5 Trends in Compound Formation
Chemical bond: holds atoms or ions together in a compound COVALENT BOND and MOLECULES Covalent bond: sharing of a pair of electrons by 2 nonmetal atoms Two or more covalently bonded atoms form a molecule Molecule: basic unit of a compound of covalently bonded atoms Consider the HCl, H2O, NH3, and CH4 molecules below Note how the chemical formula gives the actual number of each atom present in the following compounds:

20 Diatomic Molecules Recognize these elements that exist as diatomic molecules (X2):  H N O F Cl Br I2 Consider these the “diatomic seven” since there are seven of them, and six of them form a 7 on the periodic table.

21 Ions When atoms lose or gain electrons, they form charged particles called ions. Metals lose electrons  positively charged ions = cations Nonmetals gain electrons  negatively charged ions = anions Main-group elements generally form ions—i.e. gain or lose electrons—to get the same number of electrons as a Noble gas. Ions formed by main-group elements are usually isoelectronic with—i.e., have the same number of electrons as—one of the noble gases!

22 Ions Formed by Main-Group Elements
Group IA elements  +1 charge: Li+, Na+, K+, etc. (“+” = “+1”) Group IIA elements  +2 charge: Mg2+, Ca2+, Sr2+, Ba2+,etc. Group IIIA elements  +3 charge: Al3+ Group VA elements  -3 charge: N3-, P3- Group VIA elements  -2 charge: O2-, S2-, Se2- Group VIIA elements  -1 charge: F–, Cl–, Br–, I–,etc.

23 Ionic Bonds and Ionic Compounds
Another type of chemical bond: IONIC BOND Ions in an ionic compound are held together by ionic bonds. ionic bond: electrostatic attraction holding together positively charged metal cations and negatively charged nonmetal anions

24 Ionic Bonds and Ionic Compounds
Formula unit: most basic entity of an ionic compound (eg. NaCl, Al2O3, etc.) The formula gives the ratio of ions (not actual #). The 3D representation of NaCl at the right shows a network of Na+ (purple) and Cl– ions (green). The formula, NaCl, indicates a 1-to-1 ratio of Na+ ions and Cl– ions present, not the presence of only one ion of each.

25 Ionic Bonds and Ionic Compounds
An ionic compound is a network of ions, with each cation surrounded by anions, and vice versa. To melt the solid, these bonds must be broken! Ionic compounds have very high melting points compared to molecules like water.

26 2.6 Naming Compounds and Writing Their Formulas
Every element can be identified using a name, symbol, or atomic number. Know the names and symbols for the first 18 elements on the Periodic Table as well as those elements included in Figure 2.17 on p. 57, and uranium (U). The Periodic Table that will be given on quizzes and exams will include only the element symbols, atomic number, and atomic mass. Spelling counts!

27 Ionic Compounds CATIONS: positively charged ions
Metal atoms lose valence electrons to form cations. I. Groups IA, IIA, IIIA elements, silver, zinc and cadmium form only one type of ion each. Group IA elements  +1 charge always (e.g. Li+=lithium ion) Group IIA elements  +2 charge always (e.g. Mg2+=magnesium ion) Group IIIA elements  +3 charge always (e.g. Al3+=aluminum ion) silver ion = Ag+; zinc ion = Zn2+; cadmium ion = Cd2+

28 Ionic Compounds II. The Stock system is used to name transition metals, Pb, and Sn forming different charges. iron (Fe), a transition metal, forms two different ions: Fe2+ and Fe3+ lead (Pb), in Group IVA, forms two different ions: Pb2+ and Pb4+

29 Ionic Compounds ANIONS: formed only by nonmetals
When a nonmetal forms an ion, it is named: element stem name + -ide suffix + ion O = oxygen atom  O2– = oxide ion N = nitrogen atom  N3– = nitride ion

30 Polyatomic Ions Know the formulas and names of the following polyatomic ions: NH4+ = ammonium ion CO32– = carbonate ion Hg22+ = mercury (I) ion Cr2O72– = dichromate ion HCO3– = hydrogen carbonate ion SO42– = sulfate ion MnO4– = permanganate ion SO32– = sulfite ion ClO4– = perchlorate ion SCN– = thiocyanate ion O22– = peroxide ion CrO42– = chromate ion ClO– = hypochlorite ion C2H3O2– = acetate ion NO3– = nitrate ion ClO2– = chlorite ion PO43– = phosphate ion NO2– = nitrite ion ClO3– = chlorate ion CN– = cyanide ion OH– = hydroxide ion

31 Naming Ionic Compounds
1. Get the individual ions for each compound 2. CATION NAME + ANION NAME, minus “ion”  Name of compound ZnS = __________________  ______________________________ individual ions name of compound Fe2(CrO4)3 =___________________________ BaSO4 =___________________________ Ni(OH)3 =___________________________ Hg(ClO4)2 =___________________________ Cu3(PO4)2 =___________________________ CdCO3 =___________________________ PbO2 =___________________________   K2O2 =___________________________

32 Naming Ionic Compounds
Given the name of a compound, predict the formula: KNOW charges on ions formed by representative elements! KNOW how to use polyatomic ions and their charges when given to you! aluminum cyanide: __________________________________________ individual ions formula of compound copper(I) sulfide:________________  ____________________________ barium chlorate: ________________  ____________________________ zinc phosphate: ________________  ____________________________ cobalt(III) carbonate:________________  ____________________________ silver nitrate:________________  ____________________________ tin(II) permanganate:________________  ____________________________ calcium dichromate:________________  ____________________________

33 Binary Molecular Compounds
Binary molecular compounds are composed of 2 nonmetals NAMING: # of atoms of element indicated by Greek prefix before element name 1. For first element, Greek prefix + element name 2. For second element, Greek prefix + element name stem + "ide" – If only one atom present, “mono-” is usually omitted, except for CO=carbon monoxide. # of atoms Greek prefix 1 mono 6 hexa 2 di 7 hepta 3 tri 8 octa 4 tetra 9 nona 5 penta 10 deca

34 Examples Example: CO2 = carbon dioxide
CCl4 = ­_________________________ SF6= ____________________________ P4O10 =__________________________ Cl2O5= ____________________________ Some binary molecular compounds also have common names e.g. everyone knows (or should know) H2O is water Other common compounds and names you must know: NH3 = ammonia CH4 = methane H2O2 = hydrogen peroxide

35 Acids ACIDS: Aqueous solutions of a compound that releases H+ ions
usually have H in front, physical state indicated as aqueous (aq) naming depends on the ion from which the acid forms F– = fluoride ion HF(aq) = hydrofluoric acid NO2– = nitrite ion HNO2(aq) = nitrous acid NO3–= nitrate ion HNO3(aq) = nitric acid For some acids, the stem name changes: PO43– = phosphate ion H3PO4 (aq) = phosphoric acid

36 Example Problems Cl–  CO32–  SO32–  C2H3O2–  Br–  SO42–  ClO– 


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