The Components of Matter. 1. Development of atomic structure. 2. Atomic number and atomic mass. 5. Atoms and moles. 6. The periodic table

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1 Chapter 2 The Components of Matter 1. Development of atomic structure 2. Atomic number and atomic mass 3. Isotopes 4. Atomic weight 5. Atoms and moles 6. The periodic table 2.7 & 2.8 is not required. General features of the atom today. The atom is an electrically neutral, spherical entity. The atom is composed of nucleus and electrons. The atomic nucleus consists of protons and neutrons. More than one electron surround the necleus. Electrons occupy various orbitals. Nucleus (red-dot) is positively charged. Electron cloud is negatively charged. 1

2 The Modern Reassessment of the Atomic Theory All matter is composed of atoms. The atom is the smallest body that retains the unique identityof the element. Atoms of one element cannot be converted into atoms of another element in a chemical reaction. Elements can only be converted into other elements in nuclear reactions. All atoms of an element have the same number of protons and electrons, which determines the chemical behavior of the element. Isotopes of an element differ in the number of neutrons, and thus in mass number. A sample of the element is treated as though its atoms have an averagemass. Compounds are formed by the chemical combination of two or more elements in specific ratios. Properties of the Three Key Subatomic Particles Name(Symbol) Relative Charge Absolute(C)* Relative(amu) Mass Absolute(g) Location in the Atom Proton (p + ) Nucleus Neutron (n 0 ) Nucleus Electron (e - ) Outside Nucleus * The coulomb (C) is the SI unit of charge. The atomic mass unit (amu) equals g. 2

3 Atomic Symbols A Z X The Symbol of the Atom or Isotope 12 The Symbol of C 6 carbon Atom X = Atomic symbol of the element A = mass number; A = Z + N Z = atomic number (the number of protons in the nucleus) N = number of neutrons in the nucleus Isotopes A Z X The Symbol of the Atom or Isotope Isotope = atoms of an element with the same number of protons, but a different number of neutrons 3

4 Summary of Mass Terminology Term Definition Unit Isotopic mass Mass of an isotope of an element amu Atomic mass (also called atomic weight) Molecular (or formula) mass (also called molecular weight) Molar mass (M) (also called grammolecular weight) Average of the masses of the naturally occurring isotopes of an element weighted according to their abundance Sum of the atomic masses of the atoms (or ions) in a molecule (or formula unit) Mass of 1 mole of chemical entities (atoms, ions, molecules, formula units) amu amu g/mol Sample Problem Determining the Number of Subatomic Particles in the Isotopes of an Element PROBLEM: Silicon (Si) is essential to the computer industry as a major component of semiconductor chips. It has three naturally occurring isoltopes: 28 Si, 29 Si, and 30 Si. Determine the number of protons, neutrons, and electrons in each silicon isotope. PLAN: We have to use the atomic number and atomic masses. SOLUTION: The atomic number of silicon is 14. Therefore Isotope Proton Electron Neutron 28 Si 14p + 14e - 14n 0 (28-14) 29 Si 14p + 14e - 15n 0 (29-14) 30 Si 14p + 14e - 16n 0 (30-14) 4

5 Sample Problem Calculating the Atomic Mass of an Element PROBLEM: PLAN: SOLUTION: Silver (Ag: Z = 47) has 46 known isotopes, but only two occur naturally, 107 Ag and 109 Ag. Given the following mass spectrometric data, calculate the atomic mass of Ag: Isotope Mass (amu) Abundance (%) 107 Ag 109 Ag We have to find the weighted average of the isotopic masses, so we multiply each isotopic mass by its fractional abundance and thensum those isotopic portions. mass(g) of each isotope portion of atomic mass from each isotope multiply by fractional abundance of each isotope mass portion from 107 Ag = amu = 55.42amu mass portion from 109 Ag = amu = 52.45amu atomic mass of Ag = 55.42amu amu = amu atomic mass add isotopic portions Mole (mol) -the amount of a substance that contains the same number of entities as there are atoms in exactly 12 g of carbon-12. This amount is The number is called Avogadro s number and is abbreviated as N. One mole (1 mol) contains entities (to four significant figures) 5

6 Summary of Mass Terminology Term Definition Unit Isotopic mass Mass of an isotope of an element amu Atomic mass (also called atomic weight) Molecular (or formula) mass (also called molecular weight) Molar mass (M) (also called grammolecular weight) Average of the masses of the naturally occurring isotopes of an element weighted according to their abundance Sum of the atomic masses of the atoms (or ions) in a molecule (or formula unit) Mass of 1 mole of chemical entities (atoms, ions, molecules, formula units) amu amu g/mol Sample Problem Calculating the Mass and the Number of Atoms in a Given Number of Moles of an Element PROBLEM: (a) Silver (Ag) is used in jewelry and tableware but no longer in U.S. coins. How many grams of Ag are in mol of Ag? (b) Iron (Fe), the main component of steel, is the most important metal in industrial society. How many Fe atoms are in 95.8 g of Fe? PLAN: SOLUTION : PLAN: SOLUTION : 1.72mol Fe x (a) To convert mol of Ag to g we have to use the #g Ag/mol Ag, the molar mass M mol Ag x g Ag = 3.69g Ag mol Ag (b) To convert g of Fe to atoms we first have to find the #molsof Fe and then convert molsto atoms. 95.8g Fe x mol Fe 55.85g Fe 6.022x1023 atoms Fe mol Fe = 1.72mol Fe = 1.04x10 24 atoms Fe amount(mol) of Ag multiply by M of Ag (107.9g/mol) mass(g) of Ag mass(g) of Fe divide by M of Fe (55.85g/mol) amount(mol) of Fe multiply by 6.022x10 23 atoms/mol atoms of Fe 6

7 Sample Problem PROBLEM: Calculating the Moles and Number of Formula Units in a Given Mass of a Compound Ammonium carbonate is white solid that decomposes with warming. Among its many uses, it is a component of baking powder, first extinguishers, and smelling salts. How many formula unit are in 41.6 g of ammonium carbonate? PLAN: After writing the formula for the compound, we find its M by adding the masses of the elements. Convert the given mass, 41.6 g to mols using M and then the molsto formula units with Avogadro s number. SOLUTION: The formula is (NH 4 ) 2 CO 3. number of (NH 4 ) 2 CO 3 formula units M = (2 x g/mol N)+(8 x g/mol H) +(12.01 g/mol C)+(3 x g/mol O) = g/mol 2.61x10 23 formula units (NH 4 ) 2 CO 3 mass(g) of (NH 4 ) 2 CO 3 divide by M amount(mol) of (NH 4 ) 2 CO 3 multiply by 6.022x10 23 formula units/mol mol (NH 41.6 g (NH 4 ) 2 CO 3 x 4 ) 2 CO 6.022x formula units (NH 4 ) 2 CO 3 x = g (NH 4 ) 2 CO 3 mol (NH 4 ) 2 CO 3 InterconvertingMoles, Mass, and Number of Chemical Entities Mass (g) = no. of moles x no. of grams 1 mol g No. of moles = mass (g) x 1 mol no. of grams M No. of entities = no. of moles x 6.022x10 23 entities 1 mol No. of moles = no. of entities x 1 mol 6.022x10 23 entities 7

8 The modern periodic table. In the periodic table, the horizontal rows are periods, the columns are groups/families. All elements in a group have similar chemical and physical properties. Representative elements: Group A elements Transition elements: Groups 3-12 Inner transition elements: lanthanide and actinide Metallic elements: left of the stairstep line Nonmetallic elements: right of the stairstep line Metalloids: adjacent to the stairstep line (not Al) Alkali metals: 1A Alkaline earth metals: 2A Chalcogens: 6A Halogens: 7A Noble gases: 8A Rare earth metals: lanthanide Coinage metals: Cu, Ag, Au Noble metals: Ru, Os, Rh, Ir, Pd, Pt, Ag, Au, Hg 8

9 Metals, metalloids, and nonmetals. Copper Cadmium Lead Chromium Bismuth Silicon Arsenic Antimony Chlorine Bromine Sulfur Boron Tellurium Carbon (graphite) Iodine Take home message Tools of the Laboratory The Mass Spectrometer and Its Data 9

10 Take home message Laboratory preparation of molar solutions. A Weigh the solid needed. Transfer the solid to a volumetric flask that contains about half the final volume of solvent. B Dissolve the solid thoroughly by swirling. C Add solvent until the solution reaches its final volume. 10