Using the Periodic Table

Transcription

1 Quick Review - Dimensional Analysis - Density - Classification of Matter (end of Chapter 1 material) - Fundamental Laws - Dalton s Atomic Theory - Cathode-Ray Tube Experiment (J.J. Thomson) - Plum Pudding Model - Alpha-Particle Bombardment Expt. (Rutherford) - Nuclear Atom - Elemental Designation - Isotopes - Periodic Table

2 Using the Periodic Table In general: Metals form cations do not Nonmetals form anions tend to form ions

3 Simple Molecule Formation In general group 1A-7A elements react with each other to form compounds in order to achieve the same number of electrons as the noble gases. Elements can do this in one of two ways: (a) Form an ionic compound where electrons are transferred from one species to another forming oppositely charged ions. Ionic compounds are formed between metals and nonmetals. The bond that is formed is the electrostatic attraction between the cation (positive charge) and anion (negative charge). Ex. NaCl, BaCl 2, MgS (b) Form a covalent compound where electrons are shared between elements. Ex. Cl 2, H 2 O, H 2 SO 4

4 Determine Formula of Ionic Cmpd. (i) Predict stable charges of various atoms (ii) Determine ratio necessary to give a neutral compound. Examples: (a) Ca and N (b) Al and Se (c) K and O

5 Nomenclature General: 1. The first element (or cation) in the compound is named first using the base name of the element (or cation). 2. The second element (or anion) is named using the base name with a suffix (-ide, -ate, -ite)

6 Ionic Compounds 1. The cation is always written first, the anion is named second. In ionic compounds, the cation is usually a metal. When a metal is in a compound, the compound is assumed ionic. 2. The cations: (a) monoatomic metals: use base name of the metal. (b) transition metals: use base name of the metal followed by a roman numeral indicating charge. (c) polyatomic cations: the only one to memorize NH 4 + = ammonium 3. The anions: (a) monoatomic nonmetals: use the base name of the nonmetal, then add the -ide suffix. (b) polyatomic anions: memorize the anions in Table 2.5.

7 Ionic Compounds - Examples Name the following compounds: (a) NaCl (b) NH 4 NO 3 Give the molecular formula for the following compounds: (a) Aluminum oxide (b) Chromium (III) chloride (c) Sodium sulfite

8 Covalent Compounds 1. The first element in the formula is named first using the base name. 2. The second element is named like an anion (base name plus -ide suffix). 3. Use prefixes to denote numbers for cations and anions (Table 2.6) 4. The prefix mono is never used for naming the first element in a formula (it is assumed). 5. Avoid awkward pronounciations Example: CO = carbon monoxide not carbon monooxide. 6. Know common names like H 2 O = water, and C 6 H 12 O 6 = glucose; memorize the names of the acids in Table 2.7 and 2.8 (as well as HClO 4, perchloric acid).

9 Covalent Compounds - Examples Name the following compounds: (a) PCl 5 (b) SF 6 Give the molecular formula for the following compounds: (d) Tetraphosphorous decaoxide (e) Carbon dioxide

10 TO MEMORIZE (1) Names of elements 1-36 (2) Names of all alkali metals, alkaline earth metals, halogens and noble gases.

11 TO MEMORIZE

12 TO MEMORIZE (1) Identify a compound as being ionic or covalent. (2) Utilize the appropriate rules to name the compound. (3) Will also be asked to write out molecular formulas of compounds from a given name.

13 Counting by Weighing Counting individual jelly beans is a tedious process. A more efficient process would be to count by weighing. What do you need to know about each jelly bean in order to utilize this method? Need to know the average mass of a jelly bean.

14 What does this have to do w/ Chem? We count atoms in the same way! An atom is a million times smaller than the thickest human hair. We must know the average mass of atoms.

15 Atomic Mass 12 C is assigned a mass of exactly 12 atomic mass units, masses of all other atoms are relative to this standard. Mass spectrometer is used to measure accurate atomic masses.

16 Relative Atomic Masses Mass of 13 C Mass of 12 C = Mass of 13 C = ( )(12 amu) = amu The masses of all other atoms are determined in the same way.

17 Atomic Mass Question: Why is the atomic mass of carbon and not 12.00? Answer: Question: What two things do you need to know to determine average mass? Answer: Example: 98.89% (12 amu) % ( amu) = amu

18 The Mole Mole number equal to the number of carbon atoms in exactly 12 grams of pure 12 C x called Avogadro s number. A mole of anything represents x units. A mole of eggs represents x eggs. One mole of Cu, Al, Fe, S, I and Hg.

19 The Mole The mole is defined such that a sample of a natural element with a mass equal to the element s atomic mass expressed in grams contains 1 mole of atoms.

20 The Mole Since the same 12 C standard is used to define relative atomic masses and the mole, then the atomic mass of any element in units of grams will be the molar mass (mass of one mole of that substance) of that element. (6.022 x atoms) 12 amu atom = 12 g x amu = 1 g This relationship can be used to convert between atomic mass units and grams.

21 The Mole Question: A small atomic bomb requires 4.0 moles of uranium. How many grams of uranium and how many uranium atoms does 4.0 moles represent? Answer:

22 Molar Mass Molar Mass of a substance is the mass in grams of one mole of the compound. To determine molar mass of a compound we must know the molecular formula. The molecular formula tells us the actual number and kinds of atoms that make up a compound. Also tells us the mole ratios.

23 Example: H 2 SO 4 Calculation of Molar Mass

24 Review Example Chapter 3 #58: Chloral hydrate (C 2 H 3 Cl 3 O 2 ) is a drug formerly used as a sedative and hypnotic. It is the compound used to make Mickey Finns in detective stories. (a) Calculate the molar mass of chloral hydrate (b) What amount (moles) of chloral hydrate molecules are in g of chloral hydrate. (c) What is the mass in grams of 2.0 x 10-2 mol chloral hydrate? (d) What number of chlorine atoms are in 5.0 g of chloral hydrate? (e) What mass of chloral hydrate would contain 1.0 g of Cl? (f) What is the mass of exactly 500 molecules of chloral hydrate?