Chapter 2 Wed Lecture - START 4M Elements Each element has a unique number of protons in its nucleus The number of protons in the nucleus of an atom is

Chapter 2 Wed Lecture - START 4M Elements Each element has...

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2 Elements Each element has a unique number of protons in its nucleus. The number of protons in the nucleus of an atom is called the atomic number . The elements are arranged on the Periodic Table in order of their atomic numbers. Each element has a unique name and symbol. symbol either one or two letters one capital letter or one capital letter and one lowercase
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4 The Periodic Table of the Elements Some symbols are one capital letter, like C, S, and I. Others are two letters, and the second is lower case, like Br and Sr Some symbols come from the element ‘s name, like C for carbon. Others come from the Latin name of the element, like Au for gold (aurum) and Cu for copper (cuprum)
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5 Structure of the Nucleus Soddy discovered that the same element could have atoms with different masses, which he called isotopes . There are two isotopes of chlorine found in nature, one that has a mass of about 35 amu and another that weighs about 37 amu. The observed mass is a weighted average of the weights of all the naturally occurring atoms. The percentage of an element that is one isotope is called the isotope s natural abundance . The atomic mass of chlorine is 35.45 amu.
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6 Isotopes All isotopes of an element are chemically identical. undergo the exact same chemical reactions All isotopes of an element have the same number of protons. 35 Cl = 17 p+, 37 Cl = 17 p+ Isotopes of an element have different masses. 35 Cl = 34.9688amu , 37 Cl = 36.9659amu Isotopes of an element have different numbers of neutrons. 35 Cl = 18 n, 37 Cl = 20 n Isotopes are identified by their mass numbers . protons + neutrons 35 Cl = 35, 37 Cl = 37
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7 Atomic Number Number of protons Z Mass Number Protons + Neutrons Whole number A Abundance = relative amount found in a sample Isotopes
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8 Neon 9.25% 22 12 10 Ne-22 or 0.27% 21 11 10 Ne-21 or 90.48% 20 10 10 Ne-20 or Percent Natural Abundance A , Mass Number Number of Neutrons Number of Protons Symbol Ne 20 10 Ne 21 10 Ne 22 10
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9 Practice 2.3 Mass numbe= a x= chemical symbol Atomic numb=z Wht are the atomic mass and symbol for the carbon isotope with seven neutrons. See periodic table Z=6(on top of the chemical symbl) A= #protons+#neutrons=6+7=13 X=chemical sybml=C
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Practice 2.3 39 K 19 #protons= 19 39-19=20neutrons
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Page 60 Practice 2.5 Calculating atomic mass from % natural abundance of naturally occurring isotopes (use formula on page 60)
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12 Practice—Complete the Table Protons Neutrons Electrons
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