Chapter 2: Atoms, Molecules and Ions

Transcription

1 Chapter 2: Atoms, Molecules and Ions Sep 24 10:24 AM 2.1 The Early History of Chemistry The Greek did not use experiments to establish the veracity of their ideas. Alchemy "gold making juice" Khem the Egyptian word for black (the color of metals in preparation for alchemical treatment) 2.2 Fundamental Chemical Laws Objectives: The Law of Conservation of Mass The Law of Definite Proportion The Law of Multiple Proportions Natural Law Law of Conservation of Mass Established in 1789 by French Chemist Antoine Lavoisier States that mass is neither created nor destroyed in any ordinary chemical reaction. The mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants). NO MASS IS GAINED OR LOST! Example 2.2 A The Law of Conservation of Mass In a combustion reaction, 46.0 g of ethanol reacts with 96.0 g of oxygen to produce water and carbon dioxide. If 54.0 g of water is produced, how much carbon dioxide is produced? Jun 15 2:23 PM 1

2 The Law of Definite Proportion a given compound always contains exactly the same proportion of elements by mass. The law also applies to multiples of the fundamental proportion, for example: Example 2.2 B The Law of Definite Proportion A sample of chloroform is found to contain 12.0 g of carbon, g of chlorine, and 1.01 g of hydrogen. If a second sample of chloroform is found to contain 30.0 g of carbon, how many grams of chlorine and grams of hydrogen does it contain? Sep 24 12:19 PM The Law of Multiple Proportions 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 Example 2.2 C The Law of Multiple Proportions Water H 2 O, contain 2.02 g of hydrogen and 16.0 g of oxygen. Hydrogen peroxide, H 2 O 2, contains 2.02 g of hydrogen and 32.0 g of oxygen. Show how these data illustrate the law of multiple proportions. Sep 12 9:30 PM 2

3 2.3 Dalton s Atomic Theory Objectives: Ideas in Dalton's atomic theory that apply to specific chemical problems. Example 2.3 Dalton s Atomic Theory Match the chemical statement a d below with Dalton's atomic theory statement below. Chemistry a. Although graphite and diamond have different properties (due to the nature of interatomic bonding), they are both composed solely of carbon. The carbon atoms are identical. b. 2H 2 O + O 2 2H 2 O 2, not CS 2 or NaCl c. There are 6.02 x atoms in g of iron. d. C + O 2 CO 2, CO 2 is not CO, CO 3 or Fe 2 O 3 Dalton's Atomic Theories: 1. Each element is made up of tiny particles called atoms. 2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways. 3. Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative number and types of atoms. 4. 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. Sep 24 12:22 PM 2.4 Early Experiments to Characterize the Atom Thomson's cathode ray tube all atoms must contain electrons since atoms are known to be electrically neutral they must also contain some positive charge Thomson's plum pudding model of the atom. The electrons are plums dispersed in a pudding Sep 24 12:25 PM 3

4 Rutherford's gold foil experiment explained the nature of the atom as having a small, dense, positively charged nucleus surrounded by electrons moving around it at a relatively large distance. Gold Foil experiment (a) Expected Results of the Metal Foil Experiment if Thomson's Model Were Correct (b) Actual Results Sep 25 11:05 AM 2.5 The Modern View of Atomic Structure: An Introduction Objectives: Assign the correct number of protons, neutrons, and electrons to an atoms Write the symbol for an atom Do the above operations for any isotopes of an atom X = The element symbol, as read from the periodic table Z = The number of protons A = The number of protons + neutrons Isotopes atoms with the same number of protons but different numbers of neutrons Example 2.5 Protons, Neutrons, Electrons, and Symbols Sep 25 11:14 AM 4

5 2.6 Molecules and Ions Objectives: Determine if a species is an atom, molecule, or ion Determine the charge and the number of protons, neutrons, and electrons in monatomic ions. Example 2.6 A Molecule, Atom or Ion? Which of the following is an atom, an ion or a molecule? C 6 H 12 O 6 N 2 CO 3 2 Ag Fe3+ NH 4 + Sep 24 12:31 PM Example 2.6 B Protons, Neutrons, and Electrons in Ions Sep 24 12:35 PM 5

6 2.7 An Introduction to the Periodic Table Objectives: State whether an element is a metal or nonmetal and list what group it belongs to. Look at the periodic table in this section of your textbook. Please note: 1. The bold line from boron to polonium that separates metals from nonmetals 2. Group names. You will be using these designations all year 3. The various properties of each group, as described in the text 4. Groups go down, periods go across Periodic Table of Elements Chemistry: A Volatile History BBC Four Example 2.7 Identify the Element Given the following information, identify each element. a. This is the only metal in Group 6A b. This alkali metal is in the same period as iodine c. Two atoms of this element, which is in the same period as magnesium, combine with the magnesium ion to form a salt. Element Song Element Song in Japanese Sep 24 12:37 PM 2.8 Naming Simple Compounds Objectives: Binary salts Salts with polyatomic ions Binary covalent compounds Acids Naming Binary Salts A binary salt contains only one kind of cation (metal) and one kind of anion (nonmetal) Rules for Naming Binary Ionic Compounds Containing a Metal Ion With a Fixed Charge 1. The cation is written first in the name; the anion is written second in the name. 2. The name of the cation is the same as the (neutral) element from which it is derived. 3. The anion is named by adding the suffix ide to the root of the element name. Examples Name the following binary compounds: a. KCl b. NaF c. CaCl 2 d. BeO e. AlBr 3 f. Al 2 O 3 Feb 27 8:52 AM 6

7 Writting Formulas for Binary Ionic Compounds To determine the formula of binary ionic compounds remember that chemical compounds are electrically neutral. (The sum of the cation charges must equal the anion charges.) WE WILL USE THE 7 STEPS CROSS OVER RULE Rules: 1. Identify the substances as the metal and the nonmetal 2. Write their symbols 3. Write their charges (Check the periodic table) 4. Cross over the charges from top to bottom 5. Remove the charge symbol (+ or ) 6. Simplify the numbers and remove the 1 s. 7. Write the formula for the compound. Oct 1 8:41 AM Example: Formulas of Binary Ionic Compounds 1. Determine the formula for each of the following sets of atoms when they combine to from a binary ionic compound. a. K and Br b. Sr and F c. Al and Se d. Ba and O 2. Write the formula for the given names. a. Calcium Oxide b. Magnesium Chloride c. Barium fluoride d. Potassium phosphide e. Sodium Sulfide f. Lithium oxide Oct 1 8:49 AM 7

8 Naming Binary Salts for Metals with more than one charge For metals that can have more than one charge the name of the metal is succeeded by the Roman numerals in brackets OR The Stock's System by using the suffix ous for the lowest charge and ic for the highest charge and sometimes with the Latinised name for the metal Oct 1 7:27 AM Sep 24 12:46 PM 8

9 2.8 C Examples Write the formula for the given names. a. Iron III sulfide b. Iron II Sulfide c. Copper I chloride d. Copper II chloride Examples Name the following compounds: a. CuF 2 b. CuBr c. HgO d. PbO e. PbO 2 f. CuCl 2 g. SnCl 4 h. FeF 3 i. Co 2 O 3 j. Mn 2O 7 Oct 1 9:00 AM Naming Ternary Salts Ternary compounds are compounds that consist of more than two elements. In naming and writing the formulae for ternary compounds, we follow rules that are similar to binary compounds. Rules for Naming Ternary Salts: 1. Decide if the metal is a metal with fixed or variable charge. 2. Name the metal, following the rules in naming for: * metal with fixed ionic charge, or * metal with variable charge (roman #) 3. Name the metal followed by the name of the polyatomic anion. 4. For compounds containing NH 4 + cations: * Name the cation first followed by the anion (remember that for simple anion, the ending is in ide ). Oct 1 9:06 AM 9

10 Example 2.8 D Naming Compounds with Polyatomic Ions Name the following compounds: a. KMnO 4 b. Ba(OH) 2 c. Fe(OH) 3 d. NaH 2PO 4 e. (NH 4) 2 Cr 2 O 7 f. NaBrO 3 g. KIO 3 h. Ca(OCl) 2 i. Cr(NO 3) 3 Sep 24 12:48 PM Witting Formulas for Ternary Salts: WE WILL USE THE 8 STEPS CROSS OVER RULE Rules: 1. Identify the substances as the metal and the polyatomic ion 2. Write their symbols 3. Write their charges 4. Cross over the charges from top to bottom. 5. Remove the charge symbol (+ or ) 6. If more than one polyatomic ion is used place ( ) around it. Write a subscript after the ( ) x 7. Simplify the numbers and remove the 1's. 8. Write the formula for the compound. Examples Write the formula for the given names. a. lithium carbonate b. calcium nitrate c. sodium sulfate d. barium hydroxide e. Iron II phosphate Oct 1 9:13 AM 10

11 Example 2.8 E Naming Binary Covalent Compounds Name the following compounds: a. CO 2 b. P 2O 5 c. N 2 O 3 d. Cl 2O 7 e. SO 3 f. BrF 3 Example 2.8 F Naming Acids Name the following acids: a. HF b. HC 2 H 3 O 2 c. HBrO 3 d. HBrO e. HI f. HNO 2 Sep 24 12:46 PM Example 2.8 F Trying it all Together Name the following compounds: a. PCl 5 b. HClO 2 c. Ni(NO 3) 2 d. Sb 2S 3 e. XeF 4 f. NH 4OH g. NaC 2 H 3 O 2 h. NaHCO 3 i. LiH Sep 24 12:46 PM 11

12 Example 2.8 H Formulas from Names Write the formulas for each compounds: a. sodium chloride b. calcium chloride c. iron(iii) nitrate d. copper (I) chloride e. hypoiodous acid f. tin(iv) oxide g. dinitrogen tetroxide h. ammonium acetate Sep 24 12:44 PM Naming Hydrates There are many solid compounds that release water when heated at fairly low temperatures. In these compounds the water molecules are loosely bonded within the solid crystal at regular intervals. The table shows the prefixes which are used to indicate the number of water molecules. Practice Sep 22 10:09 PM 12

13 Naming Hydrocarbons Alkanes Hydrocarbons having single bond functional groups are classified as alkanes where the carbon atoms of the molecule are arranged in chains. These formulas all fit the CnH2n+2 rule. This is also the highest possible H/C ratio for a stable hydrocarbon. Since the H/C ratio in these compounds is at a maximum, we call them saturated (with hydrogen). Oct 1 7:28 AM Alkenes and Alkynes Alkenes and alkynes are hydrocarbons which respectively have carboncarbon double bond and carbon carbon triple bond functional groups. The molecular formulas of these unsaturated hydrocarbons reflect the multiple bonding of the functional groups: Alcohols All Alcohols contain the hydroxyl functional group, O H, attached to single bonded hydrocarbons (alkanes). Alcohol has the general formula R OH where R represents any chain of carbon and hydrogen atoms. The four most common Alcohols are: CH3OH Methanol CH3CH2OH Ethanol CH3CH2CH2OH Propanol Oct 1 7:28 AM 13