STUDY GUIDE SECTION 3-1 Dalton’s Atomic Theory 1. All matter is composed of indivisible, extremely small particles called atoms. 2. Atoms are indestructible and unchangeable. Chemical reactions involve the combination of atoms, not the destruction of atoms. 3. All atoms of a given element are identical. Atoms of different elements have different properties. 4. Compounds are formed when atoms of different elements combine chemically. When elements react to form compounds, they react in defined, whole number ratios. 5. In chemical reactions, atoms are combined, separated, or rearranged. Modern Atomic Theory 1. All matter is made up of very small particles called atoms. 2. Atoms of the same element have the same chemical properties, while atoms of different elements have different chemical properties. 3. While individual atoms of a given element may not all have the same mass (due to differences in nuclear structure), any natural sample of the element will have a definite average mass that is characteristic of the element and different from that of any other element. 4. Compounds are formed when atoms of two or more elements unite, with each atom losing its characteristic properties as a result of this combination. 5. Atoms are not subdivided in physical or chemical reactions. Law of Conservation of Mass: The total mass of a system remains the same whether the elements are combined, separated, or rearranged A + 1 mass unit AB B AB + 3 mass units A B + 4 mass units 4 mass units1 mass unit + 3 mass units AB 4 mass units + AC + 5 mass units AA + BC 2 mass units + 7 mass units LAW OF DEFINITE COMPOSITION: A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound. LAW OF MULTIPLE PROPORTIONS: If two or more different compounds are composed off the same two elements, the masses of the second element combined with a certain mass of the first element can be expressed as ratios of small whole numbers CO A + B 1unit + 3 units 4units CO2 A +2BAB2 carbon monoxide AB carbon dioxide 3-2 Structure of the Atom Atom: smallest particles of an element that can exist either alone or in combination with other atoms. Atomic Structure: Nucleus 1. contains neutrons & protons 2. positively charged dense central portion of the atom 3. contains nearly all the atom’s mass, but takes up a very little volume of the atom—nearly 99.9% of mass is in the atom’s nucleus Neutron electrically neutral subatomic particles in nucleus the mass of a neutron is about the same as the mass of a proton (1.675 x 10-24g) relative charge 0 mass number 1 relative mass 1.00866 u symbols, no, 1n 0 Proton positively charged subatomic particles in nucleus that have a charge equal in magnitude to the negative charge of the electron mass is 1.673 x 10-24 g mass is 1836 times greater than an electron electric charge +1 mass number 1 relative mass 1.007276 u symbol 1H , p+ 1 Electron surround the nucleus negatively charged subatomic particles very large area compared to the nucleus relative electric charge –1 mass number 1 relative mass 0.000 548 6 u actual mass 9.109 x 10-28 g symbol e-, 0e -1 DISCOVERY OF SUBATOMIC PARTICLES: J.J. Thompson (Crooke’s Tube—Cathode Ray Tube) subjected cathode rays to magnetic and electrical fields and measured their deflection. discovered that these rays were electrons. determined the ratio of the electrical charge (q) to mass (m) q/m Anode: A positive electrode; the electrode where oxidation occurs (lose an electron become positive) Cathode: A negative electrode; the electrode where reduction occurs (gain an electron become negative). Cathode Ray: The beam of electrons in a gas discharge tube. Millikan: Oil Drop Experment confirmed Thompson’s ideas determined the charge on an electron (-1 or 1.5921 x 10-19 Coulomb) determined the mass of an electron (0.000549amu or 1/1850 amu or 9.109 x 10-28g) Chadwick discovered the neutron charge q=0 mass=1amu=1.675 x 10-24 g Rutherford GOLD FOIL EXPERIMENT determined the atom consisted of a small nucleus nucleus consists of some protons and some neutral mass nucleus surrounded by orbiting electrons ISOTOPES OF Hydrogen Isotope: Atoms of the same element that differ in mass; they have the same number of protons, but a different number of neutrons Protium: nucleus consists of one proton only, has one electron (99.985% of Hydrogen is protium) Deuterium: has one proton and one neutron in the nucleus and one electron Tritium: radioactive, contains one proton, two neutrons, and one electron NUCLEAR FORCES: short-range proton-proton, neutron-proton, neutron-neutron forces that hold the nucleus together METHODS TO DESIGNATE ISOTOPES: Hyphen notation: protium Hydrogen-1 Deuterium Hydrogen-2 Tritium Hydrogen-3 Nuclear symbol: protium 1H 1 Deuterium 1H 2 Tritium 1H 3 3-3 WEIGHING and COUNTING ATOMS Atomic number (Z): the number of protons in the nucleus of each atom of that element 3 Li Lithium 6.941 [He]2s1 Example: lithium—atomic number is 3 How many protons in Lithium? 3 THE NUMBER OF PROTONS DETERMINES THE IDENTITY OF THE ELEMENT Neutral atoms: no overall charge—electrically neutral Same number of protons and electrons EXAMPLES: lithium—atomic number is 3 How many electrons in Lithium? 3 How many electrons in H? 1 How many electrons in Beryllium? 4 What element has 47 electrons? Silver MASS NUMBER: the total number of protons and neutrons in the nucleus of an atom Example: lithium—mass number is 7 How many neutrons in Lithium? 4 How many neutrons in H? 0 How many neutrons in Beryllium? 5 Isotopes: atoms of the same element that have different masses (due to a different number of neutrons) Nuclide: a general term for any isotope of any element PROBLEM: How many protons, electrons, and neutrons are there in an atom of chlorine37? RELATIVE ATOMIC MASSES: Relative means in relation to more convenient to use standard of measurement—Carbon-12 A single nuclide C-12 is assigned a mass of EXACTLY 12 atomic mass units. Atomic mass unit symbol u ONE ATOMIC MASS UNIT, 1u, is EXACTLY 1/12 the mass of a carbon-12 atom, or 1.6605402 x 10-24 gram. The mass of an atom expressed in atomic mass units is called the ATOMIC MASS of the atom. Hydrogen has an atomic mass about 1/12th of a C-12, or 1 amu, 1u AVERAGE ATOMIC MASS: is the weighted average of the atomic masses of the naturally occurring isotopes of an element Calculation of a weighted average Example: Copper Cu-63 69.17% 62.939598 u Cu-65 30.83% 64.927793u .69l7 x 62.939598 u = 43.54 u .3083 x 64.927793 u = 20.01 u total =63.55 u Individual atomic mass-Exact mass in atomic mass units of one atom (different for isotopes of same element) Average atomic mass—Average mass in atomic mass units of all natural isotopes on an element Mass Number—Total number of protons and neutrons in a nucleus of an isotope (it is the average atomic mass rounded off to the nearest whole number) Atomic Number—Number of protons in an element The mole: is the amount of a substance that contains the same number of particles as the number of atoms in exactly 12-g of carbon-12. The abbreviation for mole is mol Avogadro’s number: 6.022 137 x 1023 particles in one mole of a pure substance In terms of units 6.022 137 x 1023 particles/mole Molar mass: is the mass in grams of one mole of a pure substance. EXAMPLES: How many grams of helium contain Avogadro’s number of helium atoms? 4.00 g CONVERSION FACTORS: THIS IS A MOLMASS problem If you have 2.00 mol of He, how many grams do you have? 4.00 g He/1.00 mol He x 2.00 mol He = 8.00 g He What is the mass in grams of 3.50 mol of the element copper? 3.50 mol Cu x 63.5 grams Cu = 222 g Cu mol Cu This is a massmole problem EXAMPLE: A chemist produced 11.9 grams of aluminum. How many moles of aluminum have been produced? 11.9 g of Al x one mol Al = 0.441 mol Al 27.0 g of Al Atoms moles How many moles of silver are in 3.01 x 1023 atoms? 3.01 x 1023 atom Ag x one mol Ag = .500 mol Ag 6.023 x 1023 atoms Ag atomsmolesmass SAMPLE PROBLEM: What is the mass in grams of 1.20 x 108 atoms of copper? 1.20x108Cu atoms x 1mol Cu x 63.5 g Cu =1.27x10-14gCu 6.023x1023Cu atoms mol Cu ATOMIC MASS (or weight) (symbol A) the number of protons plus the number of neutrons in the (average mass is in the periodic table) # of Neutrons (n) = A - Z nucleus of an atom.