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Ch2_Atoms - ATOMS AND ELEMENTS Radioactivity • One of the...

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Unformatted text preview: ATOMS AND ELEMENTS Radioactivity • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876Marie (18761934). • She discovered radioactivity , radioactivity the spontaneous disintegration of some elements into smaller pieces. ATOMIC COMPOSITION • Protons – + electrical charge – mass = 1.672623 x 10-24 g – relative mass = 1.007 atomic mass units (amu) (amu) • Electrons negative electrical charge – relative mass = 0.0005 amu – • Neutrons no electrical charge – mass = 1.009 amu – ATOM COMPOSITION The atom is mostly empty space •protons and neutrons in the nucleus. •the number of electrons is equal to the number of protons. •electrons in space around the nucleus. •extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. The modern view of the atom was developed by Ernest Rutherford Canterbury University in Christchurch, NZ Ernest Rutherford (1871-1937). Rutherford birthplace, Nelson, NZ Page 1 The modern view of the atom was developed by Ernest Rutherford (1871-1937). (1871-1937). The modern view of the atom was developed by Ernest Rutherford (1871-1937). (1871-1937). Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al 26.9815 atomic number symbol atomic weight Mass Number, A • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units Isotopes • Atoms of the same element (same Z) but different mass number (A). • Boron-10 ( 10B) has 5 p and 5 n • Boron-11 ( 11B) has 5 p and 6 n 11B Boron in Death Valley • Mass Number = # protons + # neutrons protons • A boron atom can have A = 5 p + 5 n = 10 amu A Z 10 5 B 10B Page 2 Isotopes & Their Uses An MRI image of a guinea pig lung done using “hyperpolarized” hyperpolarized” helium-3. Ar-129 is Ar-129 also used. See wwwcivm.mc.duke.edu/ civmProjects Isotopes 10B 11B Periodic Table • Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their atomic weights. • We now know that element properties are periodic functions of their ATOMIC NUMBERS. NUMBERS. • See CD-ROM, Screen 2.16. • Because of the existence of isotopes, the mass of a collection of atoms has an average value. • Average mass = ATOMIC WEIGHT ATOMIC 10 11 11 • Boron is 20% 10B and 80% 11B. That is, 11B is 80 percent abundant on earth. • For boron atomic weight = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu amu) amu) Periods in the Periodic Table Groups in the Periodic Table Group 1A: Alkali Metals 1A: Reaction of potassium + H 2O Cutting sodium metal Page 3 Group 3A: B, Al, Ga, In, Tl Ga, Magnesium Group 4A: C, Si, Ge, Sn, Pb Si, Ge, Sn, Quartz, SiO 2 Magnesium oxide Aluminum Boron halides, BF3 & BI3 BI Diamond from http://cnst.rice.edu/images Group 5A: N, P, As, Sb, Bi Sb, From the Comic Book Periodic Table Ammonia, NH 3 White and red phosphorus Page 4 Group 6A: O, S, Se, Te, Po Te, Group 7A: F, Cl, Br, I, At Cl, Group 8A: He, Ne, Ar, Kr, Xe, Rn Ne, Ar, Xe, • Lighter than air balloons • “Neon” signs Shuttle main engines use H2 and O2 and Sulfur XeOF 4 Transition Elements From the Comic Book Periodic Table Lanthanides and actinides Iron in air gives iron(III) oxide Page 5 ...
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