Naming and Counting Atoms and Molecules. Chemistry--Unit 2

Transcription

1 Naming and Counting Atoms and Molecules Chemistry--Unit 2

2 Masses of 22.4 L O 2, N 2, & HCl N 2 28 g O 2 32 g HCl 36.5 g Observation: At 1 atmosphere pressure and 0 o C, 22.4 L of 3 different gases have 3 different masses. Can you make any possible inferences?

3 Metallic and Nonmetallic Elements

4 Dalton s Model of the Atom Matter is composed of tiny indivisible atoms. Atoms are not created or destroyed. Atoms of the same element have properties (e.g. mass) that are identical. Compounds are formed when atoms of different elements combine in a definite proportion. Atoms are rearranged in chemical reactions.

5 Dalton s Model: Elements and Compounds Elements Contain only one type of atom Compounds Package of two or more types of atoms

6 Dalton s Model: Chemical Reactions Rearrangement of atoms

7 Electron / Proton Model of Matter There are two types of charges: Positive (+) and Negative (-). Unlike charges attract while like charges repel. Atoms contain both positively charged particles (protons) and negatively charged particles (electrons). Atoms and Molecules are electrically neutral because the contain the same number of protons and electrons.

8 Electron / Proton Model of Matter The number of protons in an atom or are fixed cannot change. The number of electrons in atom can change. Atoms lose electrons to become (+). Atoms gain electrons to become (-). Charged atoms or molecules are called ions. (+) ions are called cations and (-) ions are called anions.

9 Molecular Vs Ionic Compounds Some Metal Ions (cations) Sodium Na 1+ Potassium K 1+ Magnesium Mg 2+ Calcium Ca 2+ Aluminum Al 3+ Copper (I) Cu 1+ Copper (II) Cu 2+ Ammonium* NH 4 1+ * A nonmetallic cation Some Nonmetal Ions (anions) Chloride Cl 1- Iodide I 1- Oxide O 2- Acetate C 2 H 3 O 1-2 Sulfate SO 2-4 Sulfite SO 2-3 Nitrate NO 1-3 Nitrite NO 1-2

10 Recognizing Ionic and Molecular Compounds Molecular Compounds Do not conduct electricity when dissolved in water Composed of nonmetallic elements Fundamental particles are molecules e.g. O 2, CO 2, C 6 H 12 O 6 Ionic Compounds Conduct electricity when dissolved in water ections/projectfolder/flashfiles/thermochem /solutionsalt.html Composed of metal ions and a nonmetal ions Fundamental particles are ions e.g. NaCl, K 2 O, Mg(NO 3 ) 2

11 Naming Binary Molec. Cmpds. Elements are listed in order. Prefixes at right the number of atoms in the compound. The ending of the last element is dropped and changed to ide The mono- prefix is generally not used in front of the 1 st element in the compound. Prefixes: 1 mono - 2 di - 3 tri - 4 tetra - 5 penta - 6 hexa - 7 septa - 8 octa - 9 nona - 10 deca -

12 Naming Binary Molec. Cmpds. Names Nitrogen dioxide Formulas NO 2 Dinitrogen pentoxide N 2 O 5 Tetraphosphorus decoxide P 4 O 10 Sulfur hexafluoride SF 6 Formulas IF 7 Iodine hexafluoride AsCl 3 Arsenic trichloride Names N 2 H 4 Dinitrogen tetrahydride PCl 5 Phosphorus pentachloride

13 Naming Ionic Compounds Refer to your ion sheet! 1. The first element is the metal cation look up the name and write it down. 2. The rest of the compound is the nonmetal anion look up the name and write it down. 3. Make sure that the ion charges balance. MgCl 2 MgCl 2 Mg +2 = Magnesium Cl 2 (there is no Cl 2!) Cl -1 = Chloride Mg +2 + Cl -1 + Cl -1 = MgCl 2 Name = Magnesum Chloride Cu(NO 3 ) 2 Cu(NO 3 ) 2 Cu = Cu +1 or Cu +2 = Copper (I) or Copper (II) NO 3-1 = Nitrate Cu +2 + NO NO 3-1 = Cu(NO 3 ) 2 Name = Copper (II) Nitrate

14 Writing Formulas for Ionic Cmpds Refer to your ion sheet! 1. Look up the symbol of the first element the cation. 2. Look up the symbol of the rest of the compound the anion. 3. Multiply the cation and anion by the number needed to achieve their least common multiple. 4. Write the formula using the multipliers as subscripts. Group polyatomic ions with parentheses. Aluminum Sulfate Aluminum = Al 3+ Sulfate = SO 4 2- LCM = 6... x Al 3+ by 2... x SO 4 2- by 3 Formula = Al 2 (SO 4 ) 3 Iron (III) Bromide Iron (III) = Fe 3+ Bromide = Br 1- LCM = 3... x Fe 3+ by 1... x Br 1- by 3 Formula = Fe(Br) 3

15 The Mole 1 mole = 1 mole = 1 mole = 6.02 x atoms, molecules, or ions 22.4 L of any gas at 1 atm and 0 o C the total mass (g) of the atoms in the substance as found on the periodic table

16 Calculations with Moles e.g. Find the mass of one mole of the following: He 4 g/mol N 2 14g/mol x 2 = 28 g/mol P 4 31 g/mol x 4 = 124 g/mol Carbon Monoxide Formula = CO 12 g/mol + 16 gmol = 28 g/mol NaCl 23 g/mol g/mol = 58.5 g/mol Fe (SO 4 ) 2 56 g/mol + 32 g/mol x g/mol x 8 = 248 g/mol Barium Fluoride Formula = BaF 2 56 g/mol + 19 g/mol x 2 = 94 g/mol Chromium (II) Oxide Formula = CrO 52 g/mol + 16 g/mol = 68 g/mol

17 More Calculations with Moles Mass (g) x 1mole molar mass (P table) x 10 particles x 1mole # Atoms, Molecules, or Ions molar mass x ( P table ) 1mole Moles 1mol x x 10 particles 1mole x 22.4 L 22.4 L x 1mole Gas Volume at 1 atm, 0 o C

18 Empirical Formulas A molecular formula denotes the number or atoms of each element in a compound. An empirical formula is the smallest whole number ratio of elements in a compound. e.g. Ethane molecular formula = C 2 H 6 Empirical formula = CH 3

19 Determining Empirical Formulas Empirical formulas are determined by decomposing compounds and Finding the mass of their elements. 2. Changing the masses into moles. 3. Finding the smallest whole number ratio of the elements. 4. Formula = the ratio of elements. Example: A compound of carbon and oxygen is decomposed to make 6 g of C and 16 g of O. Find the empirical formula. 1. C = 6 g and O = 16 g 2. 6 g C 1mole C x 0.5 mol C 1 12 g C g O 1 x 1mole O 16 g O O 0.5 mol mol O 1.0 mol C mol O 1.0 mol O 4. Empirical Formula = CO 2