1 Chapter 3 Atoms and Elements 3.4 The Atom Copyright © 2009 by Pearson Education, Inc.

2 Dalton’s Atomic Theory In Dalton’s atomic theory, atoms are tiny particles of matter. of an element are similar and different from other elements. of two or more different elements combine to form compounds. are rearranged to form new combinations in a chemical reaction.

3 Subatomic Particles Atoms contain subatomic particles. Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons are neutral. Like charges repel and unlike charges attract.

4 Rutherford’s Gold Foil Experiment In Rutherford’s gold foil experiment, positively charged particles were aimed at atoms of gold. mostly went straight through the atoms. were deflected only occasionally. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.

5 Rutherford’s Gold Foil Experiment Copyright © 2009 by Pearson Education, Inc.

6 Structure of the Atom An atom consists of a nucleus that contains protons and neutrons. of electrons in a large, empty space around the nucleus. Copyright © 2009 by Pearson Education, Inc.

7 Atomic Mass Scale On the atomic mass scale, 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom. a proton has a mass of about 1 (1.007) amu. a neutron has a mass of about 1 (1.008) amu. an electron has a very small mass, amu.

8 Particles in the Atom

9 Learning Check Identify each statement as describing a 1) proton, 2) neutron, or 3) electron. A. found outside the nucleus B. has a positive charge C. is neutral D. found in the nucleus

Learning Check Is each of the following statements true or false? Protons are heavier than electrons Protons are attracted to neutrons Electrons are small that they have no electrical charge The nucleus contains all the protons and neutrons of an atom 10

11 Chapter 3 Atoms and Elements 3.5 Atomic Number and Mass Number Copyright © 2009 by Pearson Education, Inc.

12 The atomic number is specific for each element. is the same for all atoms of an element. is equal to the number of protons in an atom. appears above the symbol of an element. Atomic Number 11 Na Atomic Number Symbol

13 Examples of atomic number and number of protons: Hydrogen has atomic number 1; every H atom has one proton. Carbon has atomic number 6; every C atom has six protons. Copper has atomic number 29; every Cu atom has 29 protons. Gold has atomic number 79; every Au atom has 79 protons. Atomic Number and Protons

14 State the number of protons in each. A. A nitrogen atom 1) 5 protons 2) 7 protons 3) 14 protons B. A sulfur atom 1) 32 protons 2) 16 protons 3) 6 protons C. A barium atom 1) 137 protons 2) 81 protons 3) 56 protons Learning Check

15 An atom of an element is electrically neutral; the net charge of an atom is zero. has an equal number of protons and electrons. number of protons = number of electrons Aluminum has 13 protons and 13 electrons. The net (overall) charge is zero. 13 protons (13+) + 13 electrons (13 -) = 0 Electrons in An Atom

16 Mass Number The mass number represents the number of particles in the nucleus. is equal to the number of protons + the number of neutrons.

17 Atomic Models

18 Number of protons = Atomic number Number of protons + neutrons = Mass number Number of neutrons = mass number – atomic number (protons) Note: Mass number is given for specific isotopes only. Study Tip: Protons and Neutrons

19 An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 302) 353) 65 B. How many neutrons are in the zinc atom? 1) 302) 353) 65 C. What is the mass number of a zinc atom that has 37 neutrons? 1) 372) 653) 67 Learning Check

20 An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 142) 163) 34 B. Its mass number is 1) 142) 163) 34 C. The element is 1) Si2) Ca3) Se Learning Check

21 Chapter 3Atoms and Elements 3.6 Isotopes and Atomic Mass  24 Mg 25 Mg 26 Mg Copyright © 2009 by Pearson Education, Inc.

22 Isotopes are atoms of the same element that have different mass numbers. have the same number of protons, but different numbers of neutrons. Isotopes

23 An atomic symbol represents a particular atom of an element. gives the mass number in the upper left corner and the atomic number in the lower left corner. Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number 23 Na atomic number 11 Atomic Symbol

The atomic symbol for a specific atom of an element gives the number of protons (p + ), number of neutrons (n), and number of electrons (e - ). Information from Atomic Symbols 24

25 Examples of number of subatomic particles for atoms Atomic symbol O P Zn p + 15 p + 30 p + 8 n16 n 35 n 8 e - 15 e - 30 e - Information from Atomic Symbols

26 Naturally occurring carbon consists of three isotopes: 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of the following: 12 C 13 C 14 C protons ______ ______ ______ neutrons ______ ______ ______ electrons______ ______ ______ Learning Check

27 Write the atomic symbols for atoms with the following subatomic particles: A. 8 p +, 8 n, 8 e - ___________ B. 17p +, 20n, 17e - ___________ C. 47p +, 60 n, 47 e - ___________ Learning Check

28 Learning Check 1. Which of the pairs are isotopes of the same element? 2. In which of the pairs do both atoms have 8 neutrons? A. 15 X 15 X 8 7 B. 12 X 14 X 6 6 C. 15 X 16 X 7 8

29 Isotopes of Magnesium

30 Isotopes of Magnesium

31 Isotopes of Sulfur A sample of naturally occurring sulfur contains several isotopes with the following abundances Isotope % abundance 32 S S S S S, 33 S, 34 S, 36 S Copyright © 2009 by Pearson Education, Inc.

32 Atomic Mass The atomic mass of an element is listed below the symbol of each element on the periodic table. gives the mass of an “average” atom of each element compared to 12 C. is not the same as the mass number. Na 22.99

33 Isotopes of Some Elements and Their Atomic Mass Most elements have two or more isotopes that contribute to the atomic mass of that element.

34 Atomic Mass for Cl The atomic mass of chlorine is due to all the Cl isotopes. not a whole number. the average of two isotopes: 35 Cl and 37 Cl.

35 Using the periodic table, specify the atomic mass of each element. A.calcium__________ B. aluminum__________ C. lead__________ D. barium__________ E. iron__________ Learning Check

36 Calculating Atomic Mass The calculation for atomic mass requires the percent(%) abundance of each isotope. atomic mass of each isotope of that element. sum of the weighted averages. mass of isotope(1)x (%) + mass of isotope(2) x (%)

37 35 Cl has atomic mass amu (75.76%) and 37 C has atomic mass amu (24.24%). Use atomic mass and percent of each isotope to calculate the contribution of each isotope to the weighted average x = amu x = amu 100 Sum is atomic mass of Cl amu Calculating Atomic Mass for Cl

38 Calculating Atomic Mass Mg Isotope Mass Abundance 24 Mg = amu x 78.70/100 = amu 25 Mg = amu x 10.13/100 = amu 26 Mg = amu x 11.17/100 = amu Atomic mass (average mass) Mg = amu

39 Atomic Mass of Magnesium The atomic mass of Mg is due to all the Mg isotopes. is a weighted average. is not a whole number.

40 Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69 Ga (atomic mass ) atoms and 39.90% of 71 Ga (atomic mass ) atoms. What is the atomic mass of gallium? Learning Check

41 Chapter 3 Atoms and Elements 3.7 Electron Energy Levels Copyright © 2009 by Pearson Education, Inc.

42 Energy Levels Energy levels are assigned numbers n = 1, 2, 3, 4, and so on. increase in energy as the value of n increases. are like the rungs of a ladder with the lower energy levels nearer the nucleus.

43 Energy Levels Energy levels have a maximum number of electrons equal to 2n 2. Energy levelMaximum number of electrons n = 12(1) 2 = 2(1) = 2 n = 22(2) 2 = 2(4) = 8 n = 32(3) 2 = 2(9) = 18

44 Orbitals An orbital is a three-dimensional space around a nucleus, where an electron is most likely to be found. has a shape that represents electron density (not a path the electron follows). can hold up to 2 electrons.

45 Orbitals A p orbital has a two-lobed shape. is one of three p orbitals in each energy level from n = 2. An s orbital has a spherical shape around the nucleus. is found in each energy level.

46 Orbitals

Electron Level Arrangement In the electron level arrangement for the first 18 elements electrons are placed in energy levels (1, 2, 3, etc.), beginning with the lowest energy level there is a maximum number in each energy level. Energy levelNumber of electrons 12 (up to He) 28 (up to Ne) 38 (up to Ar) 42 (up to Ca) 47

Learning Check Write the electron level arrangement for each: 1. N 2. Cl 3. K 48

Learning Check Identify the element with each electron level arrangement: 1. 2, , 8, , 7 49

50 Chapter 3 Atoms and Elements 3.8 Periodic Trends Copyright © 2009 by Pearson Education, Inc.

51 Valence Electrons The valence electrons determine the chemical properties of the elements. are the electrons in the highest energy level. are related to the group number of the element. Example: Phosphorus has 5 valence electrons. 5 valence electrons P in Group 5A(15) 2, 8, 5

52 All the elements in a group have the same number of valence electrons. Example: Elements in group 2A (2) have two (2) valence electrons. Be2, 2 Mg 2, 8, 2 Ca 2, 8, 8, 2 Sr 2, 8, 18, 8, 2 Groups and Valence Electrons

53 Periodic Table and Valence Electrons Representative Elements Group Numbers H He 1 2 Li Be B C N O F Ne 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 Na Mg Al Si P S Cl Ar 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

54 State the number of valence electrons for each. A. O 1) 42) 63) 8 B. Al 1) 132) 33) 1 C. Cl 1) 22) 53) 7 Learning Check

55 State the number of valence electrons for each. A. calcium 1) 12) 23) 3 B. group 6A (16) 1) 22) 43) 6 C. tin 1) 22) 43) 14 Learning Check

56 For the element with the following electron arrangement: 1) State the number of valence electrons. 2) Identify the element. A. 2, 8, 5 B. 2, 8, 8, 2 C. 2, 7 Learning Check

57 Electron-Dot Symbols An electron-dot symbol shows the valence electrons around the symbol of the element. for Mg has 2 valence electrons as single dots on the sides of the symbol Mg... ·Mg · or Mg · or ·Mg or ·Mg ·

58 Writing Electron-Dot Symbols Electron-dot symbols for groups 1A (1) to 4A (14) use single dots. · · Na · · Mg · · Al · · C · · groups 5A (15) to 7A (17) use pairs and single dots. · · · · · P · : O · · ·

59 Groups and Electron-Dot Symbols In a group, all the electron-dot symbols have the same number of valence electrons (dots). Example: Atoms of elements in Group 2A (2) each have 2 valence electrons. · Be · · Mg · · Ca · · Sr · · Ba ·

60. A. X is the electron-dot symbol for 1) Na2) K3) Al.. B.. X.. is the electron-dot symbol of 1) B2) N3) P Learning Check

61 Atomic Size Atomic size is described using the atomic radius; the distance from the nucleus to the valence electrons.

62 Atomic Radius Within A Group Atomic radius increases going down each group of representative elements.

63 Atomic Radius Across a Period Going across a period from left to right, an increase in the number of protons increases attraction for valence electrons. atomic radius decreases. Copyright © 2009 by Pearson Education, Inc.

64 Learning Check Select the element in each pair with the larger atomic radius. A. Li or K B. K or Br C. P or Cl

65 Ionization Energy Ionization energy is the energy it takes to remove a valence electron. Na(g) + Energy (ionization) -> Na + (g) + e -

66 Ionization Energy In a Group Going up a group of representative elements, the distance decreases between nucleus and valence electrons. the ionization energy increases.

67 Ionization Energy Metals have lower ionization energies. Nonmetals have higher ionization energies. Copyright © 2009 by Pearson Education, Inc.

68 Learning Check Select the element in each pair with the higher ionization energy. A. Li or K B. K or Br C. P or Cl