Chapter 2: Atoms, Molecules and Ions. Dr. Pérez
Transcription
Chapter 2: Atoms, Molecules and Ions. Dr. Pérez
Dr. Pérez CHM1045 Chapter 2 pg 1 of 11 (1) Chapter 2: Atoms, Molecules and Ions Learning Goals • Brief basis of our modern atomic theory • Understand laws of • conservation of mass • definite proportion • multiple proportions • Know mass and charge of subatomic particles • Write isotopic symbols • Determine p+, no, e-, Z, and A from isotopic symbol • Understand / calculate atomic weight • Predict charge of ions • Convert between moles and number of atoms • Convert between moles and mass (2) Modern Atomic Theory Atom - ______________ ______________ of an ______________ that retains the ______________ properties of that ______________ The atoms of an element are ______________ from the atoms of another element Atomic Theory all matter is made of ______________ compounds are composed of atoms of two or more ______________ chemically combined in fixed proportions (law of definite proportion or constant composition) Nuclear Model of the Atom nucleus - ______________ & ______________ electrons - ______________ the ______________ (3) Learning Check The composition of a sample was determined in triplicate. Results: # 1 2 3 mass sample 103 g 75 g 144 g mass Cu 53 g 28 g 79 g mass C 10. g 14 g 38 g mass O 40. g 33 g 28 g The sample is a (law that allowed you to determine this) A. pure substance (law of conservation of mass) B. pure substance (law of definite proportions) C. mixture (law of conservation of mass) D. mixture (law of definite proportions) Dr. Pérez CHM1045 Chapter 2 pg 2 of 11 (4) Law of Multiple Proportions When two elements (call them A and B) form two different compounds, the masses of element B that combine with 1 g of element A can be expressed as a ratio of small whole numbers. • Result: Mass ratios are small, whole-number multiples of each other Exercise: Nitrogen monoxide and nitrogen dioxide are both gases that contain only nitrogen and oxygen. A sample of nitrogen monoxide contains 1.00 g of N and 1.14 g of O. A sample of nitrogen dioxide contains 1.00 g of N and 2.28 g of O. Show that the two obey the law of multiple proportions. EOCE: 2.29, 2.31, 2.33, 2.35, 2.37 (5) 2.6 Subatomic Particles “Chemistry, A Molecular Approach”, Tro, 2014 amu ______________________________________________________ 1 amu = 1.66053873 x 10-27 kg Dr. Pérez CHM1045 Chapter 2 pg 3 of 11 (6) Atoms and Isotopic Symbols Properties of atoms depend on the number of ____________, ____________ and ____________ it has. Atomic number – Mass number – Isotopes – Isotopic symbol - (7) Isotopic Symbols Exercise 1. Complete the table: Nuclide # p+ 95 # no # e- Cd 48 56 Ni 28 Al3+ 36 “ X” 16 17 “ X”2- 8 2. Which are isotopes? Identify the elements. EOCE 2.47, 2.51, 2.53, 2.55, 2.57, 2.61, 2.104 Atomic # Mass # Dr. Pérez CHM1045 Chapter 2 pg 4 of 11 (8) 2.7 The Periodic Table, Fig. 2.12 “Chemistry, A Molecular Approach”, Tro, 2014 (9) The Periodic Table Periods – __________ _____ Group or family – _____________ o Group number AND Group name: Dr. Pérez CHM1045 Chapter 2 pg 5 of 11 Types of Elements (10) Metals Solid elements at room temperature, except for ____________________ Tend to be shiny Silvery; gray color ____________________melting and boiling points ____________________average density ____________________conductors of heat and electricity Malleable; ductile Form ____________________ (11) Non-Metals Lack metallic properties At room temperature most are gases (all of 8 A, N, O, F, Cl, H), a few solids (C, S, P, Se, I) and one liquid (____________________) Poor conductors of heat and electricity Characteristics lower than metals Melting and boiling points, density, electric and heat conductivities Usually form ____________________ (12) Metalloids or Semimetals Have both metallic and non-metallic properties (exhibit mixed properties) B, Si, Ge, As, Sb, Te, At Most form various ions EOCE: 2.63, 2.65, 2.67, 2.69 (13) Exercise A. Classify as metal (M) , nonmetal (N) or metalloid (Md): 1. Lr ___ Os ___ H _____ Ge _____ 2. An element that is liquid at room temperature and conducts electricity. _____ 3. An element that is solid at room temperature and is a poor conductor of heat. ____ Dr. Pérez CHM1045 Chapter 2 B. Answer true (T) or false (F) regarding nitrogen and antimony. 1. They are both nonmetals. ______ 2. They are in the same group. ______ 3. They are in the same period. ______ 4. They are the same state. _____ C. Family name group number Mg Ga (14) Predicting Charges Ion charge of elements with predictable charges: EOCE: 2.59 pg 6 of 11 period Dr. Pérez CHM1045 Chapter 2 pg 7 of 11 (15) 2.8. Atomic Mass (Weight) of Elements Most elements have several ________________. The atomic mass of an element is actually an average atomic mass of its isotopes taking into _____________ their natural abundance, expressed in atomic mass units o included in periodic table 90.40% 10 Ne 20.18 neon 0.27% 9.25% Mass Spectrum of Ne Exercises: (16) Bromine (used to make silver bromide, the important component of photographic film) has two naturally occurring isotopes, Br-79 and Br-80. Br-79 has a mass of 78.918336 amu and a percent abundance of 50.69%. The other isotope has a mass of 80.916289 amu, and a percent abundance of 49.31%. Calculate the atomic mass of bromine. A. All Ga atoms weigh 69.7 amu. B. The atomic mass of Ga is the average of 68.9 and 71.9. C. The atomic mass of Ga will be closer to 69 than 71 because there are more atoms that weigh 68.9 amu. EOCE: 2.71, 2.73, 2.75, 2.77 Gallium Mass Spectrum Relative Abundance (%) (17) The mass spectrum of gallium, Ga, is shown as follows. The atomic mass of Ga is 69.7 amu. Which of the following statements is correct? 70 60 50 40 30 20 10 0 67 68 69 70 Mass (amu) 71 72 Dr. Pérez CHM1045 Chapter 2 pg 8 of 11 (18) Section 3.8 Formula Mass of a Compound • Formula Mass - the average mass of a molecule of a compound in amu • a.k.a. molecular mass or molecular weight • Sum of the atomic masses of the atoms in amu • Exercise: • Calculate the formula mass of 1 molecule of H2O EOCE 3.59 (19) 2.9 & 3.8 The Mole & Avogadro • Chemists count particles (____________, ____________, ____________, etc.) by the mole. • _________ _________ - amount of substance that contains the same number of particles as there are atoms in 12 g of ____________. • 1 mol = __________________ particles: Avogadro’s number (20) 6.022 x 1023 If you could travel at the speed of light, it would take you more than 100 billion years to travel 6.022 x 1023 meters A stack of paper with 6.022 x 1023 sheets would be so tall that it would reach from here to the sun-not just once but more than a million times 1 mole of seconds represents the span of time 4 million times as long as the earth has already existed 1 mole of marbles is enough to cover the entire earth to a depth of 50 miles (21) Moles to Units and Units to Moles • Use conversion factor 1 mol = __________ particles 1. How many moles are there in 7.95 x 1017 atoms of He? Dr. Pérez CHM1045 Chapter 2 2. How many moles of CO2 are there in 2.99 x 1052 molecules of CO2? 3. Calculate the number of magnesium atoms in 2.5 moles of Mg2N3. (22) Molar Mass Mass, in grams, contained in 1 mole (mass of 6.022 x 1023 atoms) Same as the amu but in g/mol Example: Molar mass Cl _____________ ___________ Ca _____________ __________ Al(NO3)3 _____________ __________ (23) Exercise: Moles to Grams & Grams to Moles • Use conversion factor: 1 mol = molar mass in g 1. Calculate the mass of 5.5 mol of chromium. 2. What is the amount, in moles, of 33.5 g of potassium oxide, K2O? pg 9 of 11 Dr. Pérez CHM1045 Chapter 2 (24) Putting it All Together 1. What is the mass in grams of 5.6 x 1019 molecules of CO? 2. What is the mass of 1 formula unit of CaO? 3. How many atoms of H are there in 25.0 g of C6H12? 4. How many ions of Cl- are there in 7 formula units of MgCl2? Learning Check (25) How many atoms of oxygen are there in 100.0 g of Mg3 (PO4)2? A. 2.291 x 1023 atoms O B. 2.864 x 1022 atoms O C. 1.833 x 1024 atoms O D. 3.804 x 10-1 atoms O pg 10 of 11 Dr. Pérez CHM1045 Chapter 2 (26) Which has more atoms, 10.0 g Mg or 10.0 g Ca? A. Magnesium B. Calcium C. Both have the same number of atoms. (27) Which of the following has the largest mass? A. 10.0 g Li B. 4.5 x 1024 atoms of Li C. 100.0 g Na D. 9.0 moles of K E. 2.9 x 1023 atoms Rb EOCE: 2.81, 2.83, 2.85, 2.87, 2.89, 2.91, 3.61, 3.63, 3.65, 3.67, 3.69 pg 11 of 11