chemistry laboratory report Experiment 9

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electrons in the same orbital have different rus values (one is +Yz and another -%),they are said to be paired.

Electron Configuration The energy of an electron in a hydrogen (H) atom is determined solely by its principal quantum number n. However for many-electron atoms the orbital energies depend on both the principal quantum number n andthe angular momenfum quantum number /. Thus the energy of the orbitals in a many-electron atom increases in the order: ls < 2s < 2p < 3s a 3p < 4s < 3d < 4p < 5s, and so on. This order is also the order of filling electrons into the orbitals in a many-electron atom. The guiding principle in assigning electrons to the orbitals in a many-electron atom contains a set of three ru1es called the Aufbau principle: 1. Lower-energy orbitals f,rll before higher-energy orbitals. 2. An atomic orbital can contain only two electrons, which must have opposite spins.

(Pauli exclusion principle: no two electrons in an atom can have the same four quantum numbers.)

3 . When electrons are assigne d to p, d, or f orbitals, each successive electron enters a different orbital of the subshell, each electron having the same spin as the previous one; this proceeds until the subshell is half-full, after which electrons pair in the orbitals one by one. (Hund's rule: the most stable arrangement of electrons in the subshell is that with the maximum number of unpaired electrons, all with the same spin.)

Flame Test The resultant lowest-energy electron configuration is called the ground-state configrnation of the atom. The electrons in the atom's outermost shell are called valance electrons. When the atom absorbs enough energy, one or more of the valance electrons move to a higher energy orbital, and the atom is said to be in an excited state. The excited states are generally short-lived and rapidly decay back to the ground state by releasing radiant energy in the form of light. The energy and frequency of the light that is released during the decay transition depend on the difference in energy between the ground state and the excited state. The energy difference (AQ, the frequency (v), and the wavelength (2) of the light during emission are related by the equation, LE : hv: hclTwhere h ts Planck's constant and c is the speed of light. When the wavelengths of the light emitted fall in the visible region (400-800 nm), colors willbe observed.

Atoms of certain elements emit light u'hen the elements or their compounds are heated in a gas flame. The flame takes on a distinctive color detemined by the particular element (flame test). Each atom has its characteristic emission lines, therefore flame tests can be used to detect certain elements in unknown cornpounds.

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Excited state

LE: hv: hclT trl

Ground state

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