Do atoms in excited states emit radiation randomly at any wavelength? Explain.
When going across a row of the periodic table, protons and electrons are being added and

atomic radius generally decreases (fluorine has a smaller radius than lithium, for example). When going down a column of the periodic table, protons and electrons are also being added,

but the atomic radius generally increases (iodine is larger than fluorine, for example).Explain why this is true.

When writing electron configurations we often use the shorthand form. What is the shorthand form for electron configurations? Why does it convey all of the information we

need from the long form?

Explain the difference among the terms energy level, sublevel, and orbital.

An atom is said to be in its ground state when it is in its lowest possible energy state. When an atom possesses more energy than in its ground state, the atom is said to be in an excited state.

Photons are discrete quantities of radiation. Atoms do not gain or emit radiation randomly, but rather do so only in discrete bundles of radiation called photons.

When we draw a picture of a given orbital, we are saying that there is a 90% probability of finding the electron within the region indicated in the drawing.

A particular s-subshell can hold two electrons. Any p subshell consists of three orbitals, so a given p-subshell can hold a maximum of six electrons. A particular p orbital (like any orbital) can hold only two electrons of opposite spin.

The valence electrons of an atom are the electrons in the outermost shell of the atom. The core electrons are those in principal energy levels closer to the nucleus than the outermost shell. That is, the core electrons are the electrons that are not valence electrons.

You do not need to memorize the location of every element in the periodic table. Rather, the table is arranged in terms of the electronic structure of the atoms. For example, the first horizontal row of the table corresponds to the n = 1 shell, which consists of only the 1s orbital, so there are only two elements in the row. However, the second row of the table contains eight elements because the n = 2 shell contains a total of four orbitals (the 2s and the three 2p orbitals).

a. Na: 1s²2s²2p⁶3s¹

b. N: 1s²2s²2p³

c. Be: 1s²2s²

d. Sr: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s² or [Kr] 5s²

The ionization energy of an atom represents the energy required to remove an electron from the atom. The atomic radius is the distance from the center of the nucleus to the outer “edge” of the valence electrons.

As one goes from top to bottom in a vertical group in the periodic table, the ionization energies decrease; it becomes easier to remove an electron. Within a given vertical group, the atoms get progressively larger (increase in atomic radius) when going from the top of the group to the bottom. In going from left to right within a horizontal row of the elements in the periodic table, the atoms get progressively smaller.

a. atomic radius: Rb > K > Na; ionization energy: Na > K > Rb

b. atomic radius: C > O > F; ionization energy: F > O > C

c. atomic radius: Na > Si > O; ionization energy: O > Si > Na

D. atomic radius: Cs > I > O; ionization energy: O > I > Cs

An atom is promoted from its ground state to an excited state by absorbing energy. When the atom returns from an excited state to its ground state, it emits the excess energy as electromagnetic radiation.

The photons of radiation emitted by atoms are characterized by the wavelength (color) of the radiation: Longer wavelength photons carry less energy than shorter wavelength photons. The energy of a photon emitted by an atom corresponds exactly to the difference in energy between two allowed energy states in an atom. Thus, we can use the observable phenomenon of emission of light by excited atoms, to gain insight into the energy changes taking place within the atom.

The wave-mechanical model for the atom does not describe in classical terms the exact motion or trajectory of an electron as it moves around the nucleus, but rather predicts the probability of finding the electron in a particular location within the atom. The orbitals that constitute the solutions to the mathematical formulation of the wave mechanical model for the atom represent probability contour maps for finding the electrons. When we draw a particular picture of a given orbital, we are saying that there is a 90% probability of finding the electron within the region indicated in the drawing.

The three orbitals within a given p subshell are of exactly the same energy and differ only in their orientation in space, ao when we write the electron configuration of an element like N or O that has a partially-filled p subshell, we place the electrons in separate p orbitals to minimize the interelectronic repulsion. Thus, the configuration of nitrogen could be written as 1s²2s²2p_x¹2p_y¹2p_z¹ to emphasize this.

Because the first principal level consists only of the 1s orbital, the n = 1 level can contain only two electrons. The second principal level consists of the 2s orbital and the set of three 2p orbitals, so the n = 2 level can hold a maximum of [2 + 3(2)] = 8 electrons.

Because the valence electrons are in the outermost filled shell of the atom, it is these electrons that are affected by the presence of other atoms and that are gained, lost, or shared with other atoms. The periodic table is basically arranged in terms of the valence electronic configurations of the elements; elements in the same vertical group have similar configurations. For example, all the elements in Group 1A have one valence electron.

Excited atoms definitely do not emit their excess energy in a random or continuous manner. Rather, an excited atom of a given element emits only discrete photons of characteristic wavelength and energy when going back to its ground state.

Students often memorize trends for ionization energy and atomic radius, but it is also important that they can explain them. This question shows the students that we cannot merely look at the trends in terms of additional protons and electrons. Students should know that we need to consider the number of protons and the energy level of the valence electrons. If we compare the atomic radius of lithium and fluorine, the valence electrons are in the same energy level. However, fluorine has additional protons, so the “pull” from the positive nucleus to the negative electrons is greater and the electrons are held closer (smaller radius).

When comparing fluorine to iodine, it is true that iodine has additional protons (and thus a stronger “pull” from the nucleus). However, the valence electrons of iodine are at a higher

energy level than those of fluorine. Thus, the electrons are further from the nucleus for iodine

than they are in fluorine.

When writing in shorthand form, the core electrons are represented by the closest noble gas with fewer electrons. Because the chemically important electrons are the valence electrons (they are the only ones that interact in a chemical reaction), we only need to know the number of valence electrons and their orbitals, which are easily represented with the shorthand form.

The energy level can also be thought of as the energy state. Atoms have discrete energy levels. The energy levels also have sublevels, where we designate the different orbitals. For example, the second energy level has two sublevels, which are constituted by the s orbital and the p orbitals (there are three distinct p orbitals). As we go from energy level to sublevel to orbital we are further specifying the probable location of an electron.

Note