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Gems 160 - January 18, 2006 • Homework for Chapter 1 due today • Chem in the news on Friday - Sarah Roeschley • Lab handouts for Thursday • Today • Elements in our world • Ch. 2, parts of an atom • Compounds ==> • Elements ==> ?? • Atoms • Atomos - Greek for indivisible - the smallest particle of an element that we can identify as that element • How small is small ? • 14.3 billion Ni atoms equal the diameter of a nickel. What is the diameter of a single Ni atom? 5¢ 2.1 cm The diameter of a Ni atom is 1. 3% 2. 76%3. 5% 4. 3% 5. 5% 6. 8% 6.81 x 10-9 cm 6.8 x 109 cm 1.47 x 10-10 cm 1.47 x 1010 cm 3.5 x 10-10 cm 3.5 x10-12 m 1 • How small is small in terms of mass? • A nickel weighs 5.0 grams and contains 5.13 x 1022 atoms. What is the mass of a single atom? • Review use of scientific notation, see Appendix A. • Review appendix B and C for metric units and conversions. • 1 lb = 454 g, 1 kg = 1000g; How many kg is a 170 lb man? • Difference between mass and weight• Mass is a fundamental property, not affected by location defined as the resistance to acceleration • Weight results from the force of gravity acting on mass Which has the greatest weight? 1. 44% 2. 18% 3. 0% 4. 33% 5. 5% 100 g of gold on the moon 100 g of styrofoam peanuts on the lab bench 100 g of wood floating in the ocean 100 g of helium in a balloon in this room All have the same weight The world around us is composed of • Compounds ==> • Elements ==> • Atoms ==> • Use common knowledge and consult with a colleague to answer the following: 2 The most abundant element in the earths crust is 11%1. 68%2. 8% 3. 13%4. 0% 5. Silicon Iron ore Copper Oxygen Aluminum The most abundant element by weight in the ocean is 67%1. 18%2. 13%3. 3% 0% 4. 5. Hydrogen Sodium Oxygen Chlorine Water The most abundant gas in the atmosphere by volume is 1. Carbon dioxide Oxygen 46%3. Nitrogen 3% 4. Hydrogen 0% 5. Methane 0% 6. Gasoline 5% 46%2. 3 The most abundant element in the universe in terms of number of atoms is 13%1. 67%2. 8% 3. 10%4. 3% 5. Helium Hydrogen Oxygen Nitrogen Neon Two ways of seeing the world around us • Macroscopic • Microscopic • Compound: combination of • Compound: a molecule two or more elements in a formed when atoms with specific weight ratio. different atomic numbers combine in a specific ratio • Element: pure substance • Element: substance whose that cannot be decomposed or atoms all have the same converted to a simpler atomic number (number of substance. protons). • Both are characterized by • Both are characterized by the their physical and chemical nature of their sub-atomic properties structure. As a result of studies over a long time the atomic theory has been well developed - it provides a basis for understanding why different elements and compounds have the physical and chemical properties that they do • Atoms have parts – – – • Protons Neutrons Electrons Atoms have structure – – Inner nucleus with protons and neutrons Outer “orbitals” with electrons 4 • In all atoms the number of electrons equals the number of protons. • In ions the number of electrons may be less than the number of protons (cations +) or more than the number of protons (anions –) Symbolic structure for the atoms • • • • X is the element symbol A Z Z is the number of protons Z determines X - periodic table A is the sum of protons + neutron (mass number) X • Write the notation for the following: • Carbon with 6 neutrons • Carbon with 8 neutrons ! Chlorine with 18 neutrons is Cl 18 Cl 3. 1735Cl 4. 3517Cl 25% 1. 25% 2. 25% 25% 18 35 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 5 Hydrogen with 0 neutrons is H 2. 1 H 3. 01H 4. 1-1H 25% 1. 1 1 0 25% 25% 25% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Symbolic structure for the atoms • • • • • Write the notation for the following: Chlorine with 18 neutrons Chlorine with 19 neutrons Hydrogen with 0 neutrons Hydrogen with 2 neutrons • Atoms with the same number of protons but different numbers of neutrons are called isotopes Isotopes and the real world • A careful study of Cl atoms shows that 75.8% have a mass number of 35 and 24.2% have a mass number of 37. • What is the average mass number for Cl atoms? • The average mass number is the atomic weight that is found on the periodic table (sec 3.6) • Most chemical calculations are based on the atomic weight, because any sample of atoms will be an average of all the isotopes. 6 Describe the relation between the following symbols and each term in the list 84 87 88 0.5% 38 Sr, 9.9% 86 38 Sr, 7.0% 38 Sr, 82.6% 38 Sr ! • • • • • • • Atomic mass unit (amu) Atomic number Hand in your answers for these Mass number terms at the start of class on Atomic weight Friday. Go to the discussion board for a copy. Isotope Protons Neutron Periodic table and atomic structure • All protons and neutrons add to the nucleus in an equal manner • Electrons add to outer orbitals, but not all the orbitals are equal Electrons, periodic table and atomic structure • Each row in the table describes an orbital – A place where electrons are found – The orbital is also called a quantum shell • For our purposes – Row 1 = shell 1, holds up to 2 electrons – Row 2 = shell 2, holds up to 8 electrons (a set of 2 and a set of 6) – Row 3 = shell 3, holds up to 18 electrons (a set of 2, a set of 6 and a set of 10) – Row 4 = shell 4, holds up to 32 electrons 7 Electrons, periodic table and atomic structure • How are the shells different from each other – 1 is closest to the nucleus, lowest energy – 2 is further away from nucleus, more energy – 3 is further away than 2, more energy than 2 – etc 8