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Topic 2 Topic 2 Electrons in Motion Niels Bohr (1885-1962), a Danish scientist who worked with Rutherford, proposed that electrons must have enough energy.

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Topic 2 Topic 2 Topic 2: Atomic Structure Table of Contents Topic 2 Topic 2 Basic Concepts Additional Concepts.

Electrons in Motion Niels Bohr ( ), a Danish scientist who worked with Rutherford, proposed that electrons must have enough energy to keep them.

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Presentation on theme: "Topic 2 Topic 2 Electrons in Motion Niels Bohr (1885-1962), a Danish scientist who worked with Rutherford, proposed that electrons must have enough energy."— Presentation transcript:

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3 Electrons in Motion Niels Bohr ( ), a Danish scientist who worked with Rutherford, proposed that electrons must have enough energy to keep them in constant motion around the nucleus. Electrons have energy of motion that enables them to overcome the attraction of the positive nucleus. Atomic Structure: Basic Concepts Topic 2 Topic 2

4 Electrons in Motion Bohrs view of the atom, which he proposed in 1913, was called the planetary model. This energy keeps the electrons moving around the nucleus. Atomic Structure: Basic Concepts Topic 2 Topic 2

5 The Electromagnetic Spectrum To boost a satellite into a higher orbit requires energy from a rocket motor. One way to increase the energy of an electron is to supply energy in the form of high- voltage electricity. Another way is to supply electromagnetic radiation, also called radiant energy. Atomic Structure: Basic Concepts Topic 2 Topic 2

6 The Electromagnetic Spectrum Radiant energy travels in the form of waves that have both electrical and magnetic properties. These electromagnetic waves can travel through empty space, as you know from the fact that radiant energy from the sun travels to Earth every day. Atomic Structure: Basic Concepts Topic 2 Topic 2

7 The Electromagnetic Spectrum As you may already have guessed, electromagnetic waves travel through space at the speed of light, which is approximately 300 million meters per second. Speed of light is represented by the lower case letter c c= (wavelength)(frequency) Atomic Structure: Basic Concepts Topic 2 Topic 2

8 The Electromagnetic Spectrum Electromagnetic radiation includes radio waves that carry broadcasts to your radio and TV, microwave radiation used to heat food in a microwave oven, radiant heat used to toast bread, and the most familiar form, visible light. All of these forms of radiant energy are parts of a whole range of electromagnetic radiation called the electromagnetic spectrum. Atomic Structure: Basic Concepts Topic 2 Topic 2

9 The Electromagnetic Spectrum Atomic Structure: Basic Concepts Topic 2 Topic 2

10 Wavelength and Frequency Frequency is the number of waves per second. 1Hz = 1 hertz =1 wave/sec = s -1 Hertz (Hz) is the SI Unit for frequency Wavelength is the measurement of a wave. A wave is measured from crest to crest or trough to trough. Atomic Structure: Basic Concepts Topic 2 Topic 2

11 Electrons and Light The spectrum of light released from excited atoms of an element is called the emission spectrum of that element. Atomic Structure: Basic Concepts Topic 2 Topic 2

12 Evidence for Energy Levels Bohr theorized that electrons absorbed energy and moved to higher energy states. Then, these excited electrons gave off that energy as light waves when they fell back to a lower energy state. Atomic Structure: Basic Concepts Topic 2 Topic 2

13 Evidence for Energy Levels These regions of space in which electrons can move about the nucleus of an atom are called energy levels. Because electrons can have only certain amounts of energy, Bohr reasoned, they can move around the nucleus only at distances that correspond to those amounts of energy. Atomic Structure: Basic Concepts Topic 2 Topic 2

14 The Electron Cloud Model Instead, they are spherical regions of space around the nucleus in which electrons are most likely to be found. As a result of continuing research throughout the 20th century, scientists today realize that energy levels are not neat, planetlike orbits around the nucleus of an atom. Atomic Structure: Basic Concepts Topic 2 Topic 2

15 The space around the nucleus of an atom where the atoms electrons are found is called the electron cloud. The Electron Cloud Model These spherical regions where electrons travel may be depicted as clouds around the nucleus. Electrons themselves take up little space but travel rapidly through the space surrounding the nucleus. Atomic Structure: Basic Concepts Topic 2 Topic 2

16 The Electron Cloud Model Atomic Structure: Basic Concepts Topic 2 Topic 2

17 Electrons in Energy Level Each energy level can hold a limited number of electrons. How are electrons arranged in energy levels? The lowest energy level is the smallest and the closest to the nucleus. Atomic Structure: Basic Concepts Topic 2 Topic 2

18 Electrons in Energy Level The second energy level is larger because it is farther away from the nucleus. It holds a maximum of eight electrons. This first energy level holds a maximum of two electrons. The third energy level is larger still and holds a maximum of 18 electrons. Atomic Structure: Basic Concepts Topic 2 Topic 2

19 Energy Levels A hydrogen atom has only one electron. Its in the first energy level. Atomic Structure: Basic Concepts Topic 2 Topic 2

20 Electrons in Energy Level You can also use the periodic table as a tool to predict the number of valence electrons in any atom in Groups 1, 2, 13, 14, 15, 16, 17, and 18. The electrons in the outermost energy level are called valence electrons. All atoms in Group 1, like hydrogen, have one valence electron. Likewise, atoms in Group 2 have two valence electrons. Atomic Structure: Basic Concepts Topic 2 Topic 2

21 Electrons in Energy Level An oxygen atom has eight electrons. Two of these fill the first energy level, and the remaining six are in the second energy level. Atomic Structure: Basic Concepts Topic 2 Topic 2

22 Lewis Dot Diagrams Because valence electrons are so important to the behavior of an atom, it is useful to represent them with symbols. Atomic Structure: Basic Concepts Topic 2 Topic 2

23 Lewis Dot Diagrams A Lewis dot diagram illustrates valence electrons as dots (or other small symbols) around the chemical symbol of an element. Atomic Structure: Basic Concepts Topic 2 Topic 2

24 Lewis Dot Diagrams Each dot represents one valence electron. In the dot diagram, the elements symbol represents the core of the atomthe nucleus plus all the inner electrons. Atomic Structure: Basic Concepts Topic 2 Topic 2

25 Question 1 How does the atomic number of an element differ from the elements mass number? Answer The atomic number of an element is the number of protons in the nucleus. The mass number is the sum of the number of protons and neutrons. Topic 2 Topic 2 Basic Concept Questions

26 Topic 2 Topic 2 Basic Concept Questions A. Chlorine Write a Lewis dot diagram for each of the following. Question 2 C. Potassium B. Calcium

27 A. Chlorine Answer C. Potassium B. Calcium Topic 2 Topic 2 Basic Concept Questions

28 A. Ultraviolet light Give an example for each type of electromagnetic energy listed below. Question 3 C. Visible light B. Infrared light Topic 2 Topic 2 Basic Concept Questions

29 Sample answers: A. ultraviolet light: Answer the spectrum of light we see as color C. visible light: B. infrared light: part of sunlight radiant heat Topic 2 Topic 2 Basic Concept Questions

30 Topic 2 Topic 2 Atomic Structure: Additional Concepts Additional Concepts

31 Energy Levels and Sublevels Topic 2 Topic 2 Atomic Structure: Additional Concepts The emission spectrum for each element has a characteristic set of spectral lines. This means that the energy levels within the atom must also be characteristic of each element. But when scientists investigated multi- electron atoms, they found that their spectra were far more complex than would be anticipated by the simple set of energy levels predicted for hydrogen.

32 Energy Levels and Sublevels Notice that these spectra have many more lines than the spectrum of hydrogen. Topic 2 Topic 2 Atomic Structure: Additional Concepts

33 Energy Levels and Sublevels Some lines are grouped close together, and there are big gaps between these groups of lines. Topic 2 Topic 2 Atomic Structure: Additional Concepts

34 Energy Levels and Sublevels The big gaps correspond to the energy released when an electron jumps from one energy level to another. Topic 2 Topic 2 Atomic Structure: Additional Concepts

35 This suggests that sublevelsdivisions within a levelexist within a given energy level. Energy Levels and Sublevels The interpretation of the closely spaced lines is that they represent the movement of electrons from levels that are not very different in energy. Topic 2 Topic 2 Atomic Structure: Additional Concepts

36 Energy Levels and Sublevels If electrons are distributed over one or more sublevels within an energy level, then these electrons would have only slightly different energies. The energy sublevels are designated as s, p, d, or f. Topic 2 Topic 2 Atomic Structure: Additional Concepts

37 Energy Levels and Sublevels Each energy level has a specific number of sublevels, which is the same as the number of the energy level. For example, the first energy level has one sublevel. Its called the 1s sublevel. The second energy level has two sublevels, the 2s and 2p sublevels Topic 2 Topic 2 Atomic Structure: Additional Concepts

38 Energy Levels and Sublevels Within a given energy level, the energies of the sublevels, from lowest to highest, are s, p, d, and f. The third energy level has three sublevels: the 3s, 3p, and 3d sublevels; and the fourth energy level has four sublevels: the 4s, 4p, 4d, and 4f sublevels. Topic 2 Topic 2 Atomic Structure: Additional Concepts

39 The Distribution of Electrons in Energy Levels A specific number of electrons can go into each sublevel. Topic 2 Topic 2 Atomic Structure: Additional Concepts

40 The Distribution of Electrons in Energy Levels An s sublevel can have a maximum of two electrons, a p sublevel can have six electrons, Topic 2 Topic 2 Atomic Structure: Additional Concepts

41 The Distribution of Electrons in Energy Levels a d sublevel can have ten electrons, and an f sublevel can have 14 electrons. Topic 2 Topic 2 Atomic Structure: Additional Concepts

42 Orbitals This principle is known as the Heisenberg uncertainty principle. In 1932, Heisenberg was awarded the Nobel Prize in Physics for this discovery, which led to the development of the electron cloud model to describe electrons in atoms. In the 1920s, Werner Heisenberg reached the conclusion that its impossible to measure accurately both the position and energy of an electron at the same time. Topic 2 Topic 2 Atomic Structure: Additional Concepts

43 Orbitals Topic 2 Topic 2 Atomic Structure: Additional Concepts The electron cloud model is based on the probability of finding an electron in a certain region of space at any given instant. In any atom, electrons are distributed into sublevels and orbitals in the way that creates the most stable arrangement; that is, the one with lowest energy.

44 Electron Configurations This most stable arrangement of electrons in sublevels and orbitals is called an electron configuration. Electrons fill orbitals and sublevels in an orderly fashion beginning with the innermost sublevels and continuing to the outermost. Topic 2 Topic 2 Atomic Structure: Additional Concepts

45 Orbitals and the Periodic Table The periodic table is divided into blocks that show the sublevels and orbitals occupied by the electrons of the atoms. The shape of the modern periodic table is a direct result of the order in which electrons fill energy sublevels and orbitals. Topic 2 Topic 2 Atomic Structure: Additional Concepts

46 Orbitals and the Periodic Table Notice that Groups 1 and 2 (the active metals) have valence electrons in s orbitals, and Groups 13 to 18 (metals, metalloids, and nonmetals) have valence electrons in both s and p orbitals. Topic 2 Topic 2 Atomic Structure: Additional Concepts

47 Building Electron Configurations Chemical properties repeat when elements are arranged by atomic number because electron configurations repeat in a certain pattern. As you move through the table, youll notice how an elements position is related to its electron configuration. Topic 2 Topic 2 Atomic Structure: Additional Concepts

48 Building Electron Configurations This is standard notation for electron configurations. Hydrogen has a single electron in the first energy level. Its electron configuration is 1s 1. The number 1 refers to the energy level, the letter s refers to the sublevel, and the superscript refers to the number of electrons in the sublevel. Topic 2 Topic 2 Atomic Structure: Additional Concepts

49 Building Electron Configurations Helium has two electrons in the 1s orbital. Its electron configuration is 1s 2. Helium has a completely filled first energy level. When the first energy level is filled, additional electrons must go into the second energy level. Topic 2 Topic 2 Atomic Structure: Additional Concepts

50 Building Electron Configurations Lithium begins the second period. Its first two electrons fill the first energy level, so the third electron occupies the second level. Lithiums electron configuration is 1s 2 2s 1. Beryllium has two electrons in the 2s orbital, so its electron configuration is 1s 2 2s 2. Topic 2 Topic 2 Atomic Structure: Additional Concepts

51 Building Electron Configurations As you continue to move across the second period, electrons begin to enter the p orbitals. Each successive element has one more electron in the 2p orbitals. Carbon, for example, has four electrons in the second energy level. Two of these are in the 2s orbital and two are in the 2p orbitals. The electron configuration for carbon is 1s 2 2s 2 2p 2. Topic 2 Topic 2 Atomic Structure: Additional Concepts

52 Building Electron Configurations Topic 2 Topic 2 Atomic Structure: Additional Concepts

53 Building Electron Configurations At element number 10, neon, the p sublevel is filled with six electrons. The electron configuration for neon is 1s 2 2s 2 2p 6. Neon has eight valence electrons; two are in an s orbital and six are in p orbitals. Topic 2 Topic 2 Atomic Structure: Additional Concepts

54 Building Electron Configurations Notice that neons configuration has an inner core of electrons that is identical to the electron configuration in helium (1s 2 ). This insight simplifies the way electron configurations are written. Neons electron configuration can be abbreviated: [He]2s 2 2p 6. Topic 2 Topic 2 Atomic Structure: Additional Concepts

55 Building Electron Configurations Notice that elements in the same group have similar configurations. This is important because it shows that the periodic trends in properties, observed in the periodic table, are really the result of repeating patterns of electron configuration. Topic 2 Topic 2 Atomic Structure: Additional Concepts

56 Building Electron Configurations Topic 2 Topic 2 Atomic Structure: Additional Concepts

57 Noble Gases Each period ends with a noble gas, so all the noble gases have filled energy levels and, therefore, stable electron configurations. Topic 2 Topic 2 Atomic Structure: Additional Concepts

58 Noble Gases These stable electron configurations explain the lack of reactivity of the noble gases. Noble gases dont need to form chemical bonds to acquire stability. Topic 2 Topic 2 Atomic Structure: Additional Concepts

59 Transition Elements Notice in the periodic table that calcium is followed by a group of ten elements beginning with scandium and ending with zinc. These are transition elements. Now the 3d sublevel begins to fill, producing atoms with the lowest possible energy. Topic 2 Topic 2 Atomic Structure: Additional Concepts

60 Transition Elements Like most metals, the transition elements lose electrons to attain a more stable configuration. Topic 2 Topic 2 Atomic Structure: Additional Concepts

61 Inner Transition Elements The two rows beneath the main body of the periodic table are the lanthanides (atomic numbers 58 to 71) and the actinides (atomic numbers 90 to 103). These two series are called inner transition elements because their last electron occupies inner-level 4f orbitals in the sixth period and the 5f orbitals in the seventh period. Topic 2 Topic 2 Atomic Structure: Additional Concepts

62 Calculating Atomic Mass Topic 2 Topic 2 Atomic Structure: Additional Concepts

63 Calculating Atomic Mass Copper exists as a mixture of two isotopes. The lighter isotope (Cu-63), with 29 protons and 34 neutrons, makes up 69.17% of copper atoms. The heavier isotope (Cu-65), with 29 protons and 36 neutrons, constitutes the remaining 30.83% of copper atoms. Topic 2 Topic 2 Atomic Structure: Additional Concepts

64 Calculating Atomic Mass The atomic mass of Cu-63 is amu, and the atomic mass of Cu-65 is amu. Use the data above to compute the atomic mass of copper. Topic 2 Topic 2 Atomic Structure: Additional Concepts

65 Calculating Atomic Mass First, calculate the contribution of each isotope to the average atomic mass, being sure to convert each percent to a fractional abundance. Topic 2 Topic 2 Atomic Structure: Additional Concepts

66 Calculating Atomic Mass The average atomic mass of the element is the sum of the mass contributions of each isotope. Topic 2 Topic 2 Atomic Structure: Additional Concepts

67 Additional Assessment Questions Write electron configurations and abbreviated electron configurations of the following elements. Question 1 A. Boron C. Phosphorus B. Fluorine Topic 2 Topic 2

68 Answer A. Boron C. Phosphorus B. Fluorine Topic 2 Topic 2 Additional Assessment Questions

69 Question 2 The table on the next slide shows the five isotopes of germanium found in nature, the abundance of each isotope, and the atomic mass of each isotope. Topic 2 Topic 2 Additional Assessment Questions

70 Calculate the atomic mass of germanium. Topic 2 Topic 2 Additional Assessment Questions

71 Answer amu Topic 2 Topic 2

72 To advance to the next item or next page click on any of the following keys: mouse, space bar, enter, down or forward arrow. Click on this icon to return to the table of contents Click on this icon to return to the previous slide Click on this icon to move to the next slide Click on this icon to open the resources file. Help Click on this icon to go to the end of the presentation. Topic 2 Topic 2

73 End of Topic Summary File Topic 2 Topic 2


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