atomic concepts.....aim 3

What is the wave-mechanical model?

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HW From textbook “CHEMISTRY a Contemporary Approach”

 

Electron configuration

See periodic table for electron configuration of elements.

 

Electrons are located in energy levels, shells or principal quantum numbers (n).

There are 7 energy levels and each level can accommodate only a limited number of electrons according to the formula 2n2 where n = energy level.

Example

Energy level 1 can have a maximum of 2 e- [2(12) = 2]

Energy level 2 can have a maximum of 8 e- [2(22) = 8]

etc.

  

Example

           

For practical reasons the "planetary model of the atom" is often used to understand the "electron cloud model" but keep in mind that it is not the modern model of the atom.

 

Electrons in the first energy level have the lowest potential energy since they are located closest to the nucleus.

 

Problems

Pick a few elements from group 1,2 and 18 in the periodic table of elements and inspect their electron configurations.

 

The ground state refers to the state of an atom where all electrons have the lowest possible potential energy. The electron configurations in the periodic table of the elements are all ground state electron configurations.

 

When an electron gains a specific amount of energy, the electron move to a higher energy level and the atom is said to be in an excited state.

Example

 

          

Notice that one electron from the second energy level has moved to the third energy level.

The energy emitted is in the form of radiant or light energy which corresponds to a bright-line spectrum. Each element has its own signature or bright-line spectrum.

Example

When subjected to a flame, solutions containing certain metals have characteristic colors corresponding to the energy released when excited electrons return to lower energy levels.

 

Light is electromagnetic radiations of particular wavelength which could be represented as lines, as the bar codes on items in supermarkets.     

Problem 

The diagram below shows bright-line spectra of some selected elements. The unknown spectrum is a mixture of two elements, what are they?

 

       

TEST YOUR UNDERSTANDING

1/07

3 In a calcium atom in the ground state, the electrons that possess the least amount of energy are located in the

        (1) first electron shell     (2) second electron shell     (3) third electron shell     (4) fourth electron shell

6/07

31 Which electron configuration could represent a strontium atom in an excited state?

        (1) 2–8–18–7–1     (2) 2–8–18–7–3     (3) 2–8–18–8–1     (4) 2–8–18–8–2

37 Compared to an electron in the first electron shell of an atom, an electron in the third shell of the same atom has

        (1) less mass         (2) less energy         (3) more mass         (4) more energy

8/07

3 How do the energy and the most probable location of an electron in the third shell of an atom compare to the energy and the most probable location of an electron in the first shell of the same atom?

        (1) In the third shell, an electron has more energy and is closer to the nucleus.

        (2) In the third shell, an electron has more energy and is farther from the nucleus.

        (3) In the third shell, an electron has less energy and is closer to the nucleus.

        (4) In the third shell, an electron has less energy and is farther from the nucleus.

52 Write an electron configuration for an atom of aluminum-27 in an excited state.

1/06

2 An atom of oxygen is in an excited state. When an electron in this atom moves from the third shell to the second shell, energy is

    (1) emitted by the nucleus (2) emitted by the electron (3) absorbed by the nucleus (4) absorbed by the electron

31 Which electron configuration represents the electrons in an atom of chlorine in an excited state?

    (1) 2-7-7     (2) 2-7-8    (3) 2-8-7    (4) 2-8-8

6/06

50 Given the table below that shows students’ examples of proposed models of the atom:

Which model correctly describes the locations of protons and electrons in the wave-mechanical model of the atom?

    (1) A     (2) B     (3) C     (4) D

Base your answers to questions 53 and 54 on the information below.

An atom has an atomic number of 9, a mass number of 19, and an electron configuration of 2–6–1.

53 What is the total number of neutrons in this atom?

54 Explain why the number of electrons in the second and third shells shows that this atom is in an excited state.

Base your answers to questions 82 through 84 on the information below.

A glass tube is filled with hydrogen gas at low pressure. An electric current is passed through the gas, causing it to emit light. This light is passed through a prism to separate the light into the bright, colored lines of hydrogen’s visible spectrum. Each colored line corresponds to a particular wavelength of light. One of hydrogen’s spectral lines is red light with a wavelength of 656 nanometers. Tubes filled with other gases produce different bright-line spectra that are characteristic of each kind of gas. These spectra have been observed and recorded.

82 Explain, in terms of electron energy states and energy changes, how hydrogen’s brightline spectrum is produced.

83 Explain how the elements present on the surface of a star can be identified using brightline spectra.

84 A student measured the wavelength of hydrogen’s visible red spectral line to be 647 nanometers. In the space in your answer booklet, show a correct numerical setup for calculating the student’s percent error.

1/05

1 As an electron in an atom moves from the ground state to the excited state, the electron

                (1) gains energy as it moves to a higher energy level (2) gains energy as it moves to a lower energy level

                (3) loses energy as it moves to a higher energy level (4) loses energy as it moves to a lower energy level

6/05

1 In the modern wave-mechanical model of the atom, the orbitals are regions of the most probable location of

                    (1) protons (2) neutrons (3) electrons (4) positrons

33 An electron in an atom moves from the ground state to an excited state when the energy of the electron

                    (1) decreases (2) increases (3) remains the same

6/05

Base your answers to questions 51 and 52 on the diagram below, which represents an atom of magnesium-26 in the ground state.

51 What is the total number of electrons in the third shell?

52 Write an appropriate number of electrons in each shell to represent a Mg-26 atom in an excited state. Your answer may include additional shells.

1/04

Base your answers to questions 63 and 64 on the information and the bright-line spectra represented below.

Many advertising signs depend on the production of light emissions from gas-filled glass tubes that are subjected to a high-voltage source. When light emissions are passed through a spectroscope, bright-line spectra are produced.

63 Identify the two gases in the unknown mixture.
64 Explain the production of an emission spectrum in terms of the energy states of an electron.

48 Which electron configuration represents an atom of chlorine in an excited state? (1) 2-8-7 (2) 2-8-8 (3) 2-8-6-1 (4) 2-8-7-1

6/04

3 In the wave-mechanical model, an orbital is a region of space in an atom where there is
        (1) a high probability of finding an electron (2) a high probability of finding a neutron
        (3) a circular path in which electrons are found (4) a circular path in which neutrons are found

35 Which electron configuration represents the electrons of an atom in an excited state? (1) 2-4 (2) 2-6 (3) 2-7-2 (4) 2-8-2

36 In comparison to an atom of F-19 in the ground state, an atom of C-12 in the ground state has
    (1) three fewer neutrons (2) three fewer electrons (3) three more neutrons (4) three more electrons

8/04

33 When compared with the energy of an electron in the first shell of a carbon atom, the energy of an electron in the second shell of a carbon atom is  (1) less (2) greater (3) the same

35 Which electron configuration represents the electrons of an atom in an excited state?

                (1) 2–8–1         (2) 2–8–6         (3) 2–8–17–6       (4) 2–8–18–5

1/03

1 During a flame test, ions of a specific metal are heated in the flame of a gas burner. A characteristic color of light is emitted by these ions in the flame when the electrons

        (1) gain energy as they return to lower energy levels (3) emit energy as they return to lower energy levels

        (2) gain energy as they move to higher energy levels (4) emit energy as they move to higher energy levels

6/03

1 Which ion has the same electron configuration as an atom of He? (1) H-   (2) O2-   (3) Na+  (4) Ca2+

2 The region that is the most probable location of an electron in an atom is (1) the nucleus (2) an orbital (3) the excited state (4) an ion

3 When the electrons of an excited atom return to a lower energy state, the energy emitted can result in the production of

                (1) alpha particles (2) isotopes (3) protons (4) spectra

4  Base your answer on the electron configuration table shown below.

        a.  Which electron configuration represents the excited state of a calcium atom?

        b. What is the element Z?

8/03

1 Which electron transition represents a gain of energy?

                (1) from 2nd to 3rd shell (2) from 2nd to 1st shell  (3) from 3rd to 2nd shell (4) from 3rd to 1st shell

40 Which particle has the same electron configuration as a potassium ion? (1) fluoride ion (3) neon atom (2) sodium ion (4) argon atom

44 Which is an electron configuration for an atom of chlorine in the excited state? (1) 2-8-7 (2) 2-8-8 (3) 2-8-6-1 (4) 2-8-7-1

Base your answers to questions 63 and 64 on the diagram below, which shows bright-line spectra of selected elements.

 

63 Identify the two elements in the unknown spectrum.
64 Explain how a bright-line spectrum is produced, in terms of excited state and ground state.

6/02

1 The modern model of the atom shows that electrons are

        (1) orbiting the nucleus in fixed paths (3) combined with neutrons in the nucleus

        (2) found in regions called orbitals   (4) located in a solid sphere covering the nucleus

2 What is the electron configuration of a sulfur atom in the ground state?  (1) 2-4       (2) 2-6     (3) 2-8-4      (4) 2-8-6

8/02

1 Which species does not have a noble gas electron configuration? (1) Na+       (2) Mg2+        (3) Ar          (4) S

2 Which electron configuration is correct for a sodium ion? (1) 2-7        (2) 2-8     (3) 2-8-1           (4) 2-8-2

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