# Chemistry Outcomes Review: Chapter 4

## Structure of Atoms

Many properties of the elements vary in a periodic way as they increase in atomic mass (or atomic number, in the present view) and these variations are codified in periodic tables that were first devised by Mendeleev and Mayer. The fundamental basis for this periodicity is the structure of the atom which we developed in this chapter. In order to interpret atomic emission spectra, we need to understand the properties of light, and this means both its wave and photon (quantum) properties which led to a quantum model of the atom.

The discovery of the wave nature of electrons led to a wave description of atoms, which we characterized in terms of a shell structure. The electron shell model is useful for understanding and predicting a great many periodic patterns in atomic and elemental properties, but it is too simple to explain more subtle periodicities and the spins of elemental atoms. For these we need the more complete description of electron waves (orbitals) based on wave equations that describe the substructure of the shells.

Check your understanding of the ideas in this chapter by reviewing these expected outcomes of your study.

**You should be able to:**

- Identify and describe periodic patterns in atomic and elemental properties and by extrapolation or interpolation predict values of these properties for elements that have not been measured [Section 4.1].
- Calculate the wavelength, frequency, or speed of propagation of a wave, given two of the three variables or the information necessary to derive them [Section 4.2].
- Describe in pictures and/or words how superimposition of waves produces diffraction patterns when waves pass through a grating [Section 4.2].
- Identify, given the characteristics of a source or detector of radiation, where in the electromagnetic spectrum the radiation will be found [Section 4.2].
- Calculate the wavelength, frequency, or energy of a photon, given two of the three variables or the information necessary to derive them [Section 4.3].
- Show how the results of photoelectric-effect experiments can be explained by Planck's quantum hypothesis and how the wave model fails [Section 4.3].
- Identify and explain whether a phenomenon is a result of the wave or photon (quantum) properties of light [Section 4.3].
- Explain how the line emission and absorption of light by atoms requires that the energies of atoms be quantized [Section 4.4].
- Use an energy level diagram for an atom and emissions from some known energy level changes to predict the emissions from other energy level changes [Section 4.4].
- Calculate the de Broglie wavelength of any particle of known mass and velocity and identify where in the electromagnetic spectrum it will be found [Section 4.5].
- Characterize a standing wave in terms of its amplitude, wavelength, and nodal properties [Sections 4.6 and 4.10].
- Explain why the uncertainty principle leads to a probability picture of an electron wave in an atom instead of more easily visualized orbits of an electron [Section 4.6].
- Describe in pictures and/or words how vibrating objects like strings, drumheads, and gongs are related to the probability model of electron waves (orbitals) in atoms, including their sizes [Sections 4.6 and 4.10].
- Calculate or predict the direction of change for the kinetic energy, if the mass or velocity of the object changes [Section 4.7].
- Calculate or predict the direction of change for the potential energy of a system if the variables that describe the potential energy (mass, charge, distance, and so on) are changed [Section 4.7].
- Use pictures, words, and/or equations to explain how the opposing effects of potential and kinetic energies of electron waves prevent atoms from collapsing and determines their size [Section 4.7].
- Explain how the balance of potential and kinetic energies of electron waves together with the exclusion principle lead to a shell structure for atoms [Sections 4.8, 4.9, and 4.10].
- Show how the periodic properties of atoms and elements provide evidence for (or against) an electron shell and subshell model of atomic structure [Sections 4.9 and 4.10].
- Show how the electron shell model for atoms explains and predicts periodic properties of atoms and elements, including, but not limited to, atomic size, ionization energies, and electronegativities [Section 4.9].
- Describe the atomic orbitals derived from the Schrödinger wave equation for principal quantum numbers 1 and 2 [Section 4.10].
- Write the electron configurations for atoms of the first 20 elements, using the energy levels for multielectron atoms and their degeneracies and accounting for the exclusion principle and electron-electron repulsion energies [Section 4.10].
- Predict, from its electron configuration, the number of unpaired electron spins a ground-state atom has [Section 4.10].
- Describe how the electron shell model and the orbitals and energies derived from solutions to the wave equation are complementary and together provide a way to explain all the periodic properties of atoms and elements discussed in the chapter [Section 4.1, 4.8, 4.9, and 4.10]