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Atomic structure ch 4.notebook October 16, 2012 Subatomic particles Protons= positive p+ Chapter 4 Atomic Structure electrons= negative e Atomsmallest particle of an element that retains the properties of the element neutrons=neutral n0 Early atomic models Relative massessee p 106 DemocritusGreek Philosopher (460 BC370 BC) First suggested existence of atoms. Atomos = indivisible Nucleuscontains protons and neutrons electrons outside nucleus in electron cloud Dalton's Atomic theoryused experimental methods 1. All elements made of atoms 2. Atoms of same element are identical 3. Atoms of different elements can combine in whole number ratios to form compounds 4. Elements never change into different elements during a chemical reaction Atomic numbernumber of protons in nucleus each element has different atomic number See periodic table Hydrogen 1 Helium 2 Lithium 3 Oct 910:29 AM Oct 910:36 AM Protons= electrons in an atom mass number = protons + neutrons neutrons= mass number atomic number Written in shorthand: mass number as superscript atomic number as subscript 197 How many protons, neutrons and electrons: Be mass number =9 Neon mass number= 20 Au 1H H H Isotope = same element with different number of neutrons Sodium mass number = 23 Oct 910:42 AM Oct 910:46 AM p 113 1920 p 112 #1718 17. d. Br a. O e. Pb b. S c. Ag 19. oxygen16 oxygen17 oxygen18 20. chromium50 atomic number=24 chromium52 chromium53 a. carbon12 b. Fluorine19 c. beryllium9 Oct 910:48 AM Oct 122:57 PM 1 Atomic structure ch 4.notebook Atomic massdecimal number on periodic table Calculated using the weighted average of all the isotopes of an element see p 114 table October 16, 2012 p 117 Example: Copper 2 isotopes: mass #1 = 62.93 amu abundance =69.2% mass #2= 64.93 amu abundance= 39.8% Atomic mass unit (amu) defined as 1/12 the mass of a carbon12 atom. Protons= 1 amu neutrons = 1 amu electrons = negligible (almost massless) Oct 910:49 AM Example Bromine: 2 isotopes mass#1= 78.92 amu, abundance=50.69% mass #2 =80.92amu abundance= 49.31% Oct 123:02 PM Periodic Table Groupsvertical columns Periods horizontal rows Valence electrons outermost electrons used in bonding Can tell how many by group on periodic table H 1 valence electron Be 2 B 3 C 4 N 5 O 6 F 7 Ne 8 ****He only 2 Oct 910:52 AM 2
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