Energy states, 3 electrons/2 atoms

What about molecules and complex ions Absorption of light by molecules and complex ions results in the promotion of electrons to higher energy states in the same way as in atoms. However, it is more complicated because molecules and complex ions have energy states that atoms do not. 

The energy states of atoms are expressed in terms of four quantum numbers j it, the principal quantum number /, the azimuthal quantum number m, the magnetic quantum number and mt or s, the spin quantum number. According to Pauli s exclusion principle, no two electrons can have the same values for all the four quantum numbers. 

The energy states of atoms are purely electronic (atoms have of course no rotational or vibrational states) and these are obtained in a simple picture by fitting the available electrons in the available orbitals. In the ground state all... 

Chemicals react together in order to reach a lower and more stable energy state. If atoms react together they do so to achieve a stable outer electron shell of all the atoms in the new molecules (see ionic bonding and covalent bonding). 

The second class of hydrogen-like atoms is called Rydberg atoms. A Rydberg atom is an ordinary atom in which one electron has been elevated to a very high quantum state. The energy states of atoms are identified with the quantum number n, called the principal quantum number. The ground state, or lowest state, is the n = state, which is where atoms spend most of their time. The first excited state is the n = 2 energy state, the second excited state is = 3, and so on. 

As we have seen from the previous sections, spectra are derived from quantised transition between energy states in atoms and molecules. The wavelengths at which these transitions occur are dependent upon the processes undergone. Hence, electronic transitions occur at higher energies (ultraviolet) than vibrational (infrared) or rotational ones (microwave). The molecular spectra observed in the UV-visible-NIR are a combination of these transitions. The intensity of the absorption is linked to the type of transition and the probability of its occurrence. Generally speaking, those transitions that are favoured in quantum mechanical terms exhibit more intense absorption bands. 

Every atom emits characteristic X-rays with discrete energies that identify the atom like fingerprints. For every atom, the, the X-rays are identified according to the final state of the electron transition that produced them. Historically, the energy states of atomic electrons are characterized by the letters K,L,M,N,etc. The K state or K orbit or K shell is the lowest energy state, also called the ground state. The X-rays that are emitted as a result of electronic transitions to the K state, from any other initial state, are called K X-rays (Fig. 3.1). Transitions to the L state give rise to L X-rays and so on. K and Kp X-rays indicate transitions from L to K and M to K states, respectively. 

Hund s rules - A series of rules for predicting the sequence of energy states in atoms and molecules. One of the important results is that when two electrons exist in different orbitals, the state with their spins parallel (triplet state) lies at lower energy than the state with antiparallel spins (singlet). 

EHEJIES Wavelike properties of electrons help relate atomic emission spectra, energy states of atoms, and atomic orbitals. 

Flame atomic absorption spectrometry was developed in 1955 independently by Walsh in Australia (3) and by Alkemade and Milatz (4) in the Netherlands. Because electrons in quantized energy states for atoms of alkali metal elements can easily be raised to excited states (see above), flame emission spectroscopy is a more appropriate instrumental technique,... 

The second process by which the excited atom can regain stability is by transfer of an electron from one of the outer orbitals to fill the vacancy. The energy difference between the initial and final states of the transferred electron may be given off in the form of an X-ray photon. Since all emitted X-ray photons have energies proportional to the differences in the energy states of atomic electrons, the lines from a given element are characteristic of that element. The relationship between the wavelength of a characteristic X-ray photon and the atomic number Z of the element was first established by Moseley. Moseley s law is written ... 

Suppose we could excite all of the electrons in a sample of hydrogen atoms to the n = 6 level. They would then emit light as they relaxed to lower energy states. Some atoms might undergo the transition n = 6 to n = 1, and others might go from n = 6 to n = 5, then from n = 5... 

Fig. 2.8. Schematic electronic energy states of atoms (a), small molecules (b), large molecules (c), and condensed phases (d) either solid or liquid. The electronic density of states (e) corresponds to the level structure shown in (d).

Electrons exist only in very specific energy states for atoms of each element. 

We start by assuming that our sample consists of a monatomic gas, like He or Ne (or any other monatomic gas, like Hg vapor). Such a sample has only three types of energy states electronic, nuclear, and translational. Of these three, electronic and nuclear states are states within the atoms. Only translational energy states relate the position of the atom as a whole, rather than relating the relative positions of the subatomic particles of the atom. 

Quantum-mechanical theory describes the behavior of electrons in atoms. Since chemical bonding involves the transfer or sharing of electrons, quantum-mechanical theory helps us understand and describe chemical behavior. As we saw in Chapter 7, electrons in atoms exist within orbitals. An electron configuration for an atom shows the particular orbitals that electrons occupy for that atom. For example, consider the ground state—or lowest energy state—electron configuration for a hydrogen atom ... 

The thermo-chemical or the initial (neutral, un-ionized specimen with n elec-trons)-final (radiation beam ionized specimen with n — 1 electrons) states relaxation dominates the CLS [6, 7]. The energy required for removing a core electron from a surface atom is different from the energy required for a bulk atom. The surface atom is assumed as a Z -F 1 impurity sitting on the substrate metal of Z atomic number. The energy states of atoms at a flat surface or at a curved surface are expected to increase/decrease while the initial states of atoms in the bulk decreases/increase when the particle size is reduced. This mostly adopted mechanism creates the positive, negative, or mixed surface shift in theoretical calculations. 

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