Early Atomic Theory and Structure

Transcription

1 Early Atomic Theory and Structure Chapter 5 Hein and Arena Version 1.1 Eugene Passer Chemistry Department Bronx Community 1 College John Wiley and Sons, Inc

2 The Atom and its Subatomic Particles The atom is comprised of two regions; the very dense nucleus, which is at the center of the atom and the electron cloud, which surrounds the nucleus. 2

3 Atomic Structure. (electron cloud) 5.6 3

4 Electron The e - has a negative charge( assigned a relative value of -1). The e - is located outside of the nucleus. The e - is the lightest subatomic particle. 4

5 Proton The p has a positive charge, which is equal in magnitude, but opposite in sign, to the relative charge on the e -. The p is located inside of the nucleus. The p is the second heaviest subatomic particle. 5

6 Neutron The n is electrically neutral( it has no charge). The n is located inside of the nucleus. The mass of n is slightly greater than the mass of the p. 6

7 Actual charge of the e - is: x10-19 C Actual charge of the p is: x10-19 C 7

8 An atom is electrically neutral when the number of protons in the nucleus is equal to the number of electrons in the electron cloud.. (electron cloud) 5.6 8

9 Ions Ions are positively, or negatively, charged atoms, which result when a neutral atom loses, or gains, one or more electrons, respectively. 9

10 Metals typically form Cations 5.4 When a neutral metal atom loses one or more electrons, a cation is formed. 10

11 Non-metals typically form Anions 5.4 When a neutral non-metal atom gains one or more electrons, an anion is formed. 11

12 Nonmetals Metals are are found to to the left right of of the the metalloids. 12

13 Periods: Elements in the same period do not have similar chemical properties (e.g. NaCl, MgCl 2, AlCl 3, etc.). Groups (or Families): Elements in the same group have similar chemical properties (e.g. NaCl, KCl, RbCl, etc.).

14 Group # and Ionic Charge A metal atom typically loses the number of electrons necessary to achieve an electron count equal to the inert gas element nearest to it (e.g. Mg = 12-2 = 10, which is Ne); Mg Mg e - A nonmetal atom typically gains the number of electrons necessary to achieve an electron count equal to the inert gas element nearest to it (e.g. N = = 10, which is Ne); N + 3e - N -3 14

15 Question Answer What would be the correct chemical formula when the following sets of atoms or ions combine? Na and S Ca and Cl Mg and PO 4-3 Al and S Na 2 S Al 2 S 3 CaCl 2 Fe +2 and Cl Mg 3 (PO 4 ) 2 FeCl 2 Note: All compounds are electrically neutral

16 Atomic Numbers of the Elements 16

17 The atomic number of an element is equal to the number of protons in the nucleus of that element. The atomic number of an atom determines which element the atom is. 17

18 Every atom with an atomic number of 1 is a hydrogen atom. Every hydrogen atom contains 1 proton in its nucleus. 18

19 Every atom with an atomic number of 6 is a carbon atom. Every carbon atom contains 6 protons in its nucleus. 19

20 Isotopes of the Elements 20

21 Atoms of the same element can have different masses. They always have the same number of protons, but they can have different numbers of neutrons in their nuclei. The difference in the number of neutrons accounts for the difference in mass. These are isotopes of the same element. 21

22 Isotopic Notation 22

23 Isotopic Notation 6 protons + 6 neutrons 12 6C 6 protons 23

24 Isotopic Notation 6 protons + 7 neutrons 13 6C 6 protons 24

25 Isotopic Notation 6 protons + 8 neutrons 14 6C 6 protons 25

26 Spontaneous Nuclear Decay Generates New Elements 14 C 6 14 N 7 + b - 26

27 Atomic Mass 27

28 The atomic masses listed in the periodic table are not the actual masses of an atom of each element. The actual mass of one hydrogen atom was found to be x g, which is not a convenient number to work with. To overcome this problem a standard of relative atomic masses using atomic mass units was devised. 28

29 The relative standard is based on the most abundant isotope of carbon. Please recall the definition of the mole. 12 C 6 29

30 A mass of exactly 12 atomic mass units (amu) was assigned to 12 C 6 30

31 1 1 amu is defined as exactly equal to the mass of a carbon-12 atom 12 1 amu = x g 12 C 6 (12.000amu)( x10-24 g/amu) = x10-23 g

32 Relative isotopic atomic mass 1 H is: amu. 1 1 H amu/( x10-23 g) = AW H(amu) /( x10-24 g) AW 32 H = amu

33 Average Relative Atomic Mass 33

34 The listed atomic mass of an element in the periodic table is the average relative mass of the isotopes of that element compared to the mass of carbon-12 (exactly amu). 34

35 Average relative atomic mass amu. 35

36 To calculate the average atomic mass of an element, multiply the isotopic mass of each isotope by its percent abundance in decimal form and add the results. Isotope Isotopic mass (amu) Abundance (%) Average Relative atomic mass (amu) 63 Cu Cu ( amu) = amu ( amu) = amu amu 36

37 Composition of Compounds 37

38 The Law of Definite Composition A compound always contains two or more elements, except diatomics, combined in a definite proportion (i.e. % composition). 38

39 Composition of Water The Law of Definite Composition Water always contains the same two elements: hydrogen and oxygen. The percent by mass of hydrogen in water is 11.2%. The percent by mass of oxygen in water is 88.8%. Water always has these percentages. If the percentages were different, the compound would not be water. 39

40 Composition of Hydrogen Peroxide The Law of Definite Composition Hydrogen peroxide always contains the same two elements: hydrogen and oxygen. The percent by mass of hydrogen in hydrogen peroxide is 5.9%. The percent by mass of oxygen in hydrogen peroxide is 94.1%. Hydrogen peroxide always has these percentages. 40

41 The Law of Multiple Proportions Atoms of two or more elements may combine in different ratios to produce more than one compound. 41

42 The Law of Multiple Proportions The formula for water is H 2 O. Ratio of atoms of hydrogen to oxygen is 2:1 The formula for hydrogen peroxide is H 2 O 2. Ratio of atoms of hydrogen to oxygen is 1:1 42

43 The law of definite composition The law of multiple proportions 43

44 44