Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
HW due Friday 9/15/06 • Ch. 2 – 8, 13, 30,33, 41, 43, 47, 50 • Ch. 3 – 6, 13, 19, 28, 40, 46, 59, 68, 76, 83 Working with numbers: examples • Space shuttle – traveling at 1400 nautical miles per hour – was it going fast enough to escape Earth’s gravity? • Escape velocity > 10 km/s Working with numbers: examples • Density: mass density = volume m d= V • SI-derived unit is kg/m3 • Chunk of platinum metal: – Density = 21.5 g/cm3 – Volume = 4.49 cm3 – Mass? (in SI units/simplified) Three Temperature Scales • Fahrenheit • Celcius (Centigrade) – Absolute zero = -273.15°C • Kelvin (K) (SI unit) – Absolute zero = 0 K K = 0C + 273.15 273 K = 0 0C 373 K = 100 0C 0F = 9 x 0C + 32 5 32 0F = 0 0C 212 0F = 100 0C 1.7 Atoms, Molecules and Ions Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. 2. All atoms of a given element are identical. The atoms of one element are different from the atoms of all other elements. 3. Compounds are composed of atoms of more than one element, in specific ratios. 4. Chemical reactions only involve separation, combination, or rearrangement of atoms. Atoms are not created or destroyed in chemical reactions 2 Law of multiple proportions: Early argument for the existence of atoms Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. 2. All atoms of a given element are identical. The atoms of one element are different from the atoms of all other elements. 3. Compounds are composed of atoms of more than one element, in specific ratios. 4. Chemical reactions only involve separation, combination, or rearrangement of atoms. Atoms are not created or destroyed in chemical reactions 16 X + 8Y 8 X2Y Law of conservation of mass Atomic structure • Late 1800s: – Cathode ray tube experiment – Charged particles deflected toward a positive charge – Negatively charged particles: electrons J.J. Thomson, measured mass/charge of e(1906 Nobel Prize in Physics) 2.2 Atomic structure • Early 1900s: – Atom contain electrons (-) but are electrically neutral – Thomson’s ‘plum pudding’ model 2.2 Atomic structure • Rutherford used a particles (protons) to study the atom – Hypothesis: plum pudding – Prediction: positively charged particles will pass easily through the diffuse plum pudding (1908 Nobel Prize in Chemistry) a particle velocity ~ 1.4 x 107 m/s (~5% speed of light) 1. atoms positive charge is concentrated in the nucleus 2. proton (p) has opposite (+) charge of electron (-) 3. mass of p is 1840 x mass of e- (1.67 x 10-24 g) 2.2 Atomic structure • Electrons (-) + Protons (+) • Problem: – Hydrogen: one proton – Helium: two protons – But, Helium has ~4x more mass than Hydrogen • Chadwick: found the neutron – No charge / mass ~ proton Rutherford’s Model of the Atom atomic radius ~ 100 pm = 1 x 10-10 m nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m “If the atom is the Houston Astrodome, then the nucleus is a marble on the 50-yard line.” mass p = mass n = 1840 x mass e- Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei Mass Number A ZX Atomic Number 1 1H 235 92 2 1H U Element Symbol (D) 238 92 3 1H U (T) Do You Understand Isotopes? How many protons, neutrons, and electrons are 14 in 6 C ? 6 protons, 8 (14 - 6) neutrons, 6 electrons How many protons, neutrons, and electrons are 11 in 6 C ? 6 protons, 5 (11 - 6) neutrons, 6 electrons The periodic table The periodic table Group 1A: alkali metals Group 2A: alkaline earth metals Group 7A: halogens Group 8A: noble gases (rare gases) A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2 H2O NH3 CH4 A diatomic molecule contains only two atoms H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4 An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. A monatomic ion contains only one atom Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3-