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Gen. Chem.- Chapter 8

Gen. Chem.- Chapter 8 - Chapter 8 Electron Configurations...

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Chapter 8: Electron Configurations, Atomic Properties, and the Periodic Table Electron configuration - how electrons are distributed among the orbitals & subshells in the energy-level diagram of an atom. 8.1 Multielectron Atoms 4 standpoints that are relevant to the discussion in several sections of this chapter: In the hydrogen atom, all subshells are at the same energy level - the orbital energies in the hydrogen atom depend only on the principal quantum number, n. That is, we predict with the Bohr model: E n = -B/n 2 . Orbital energies are lower in the multielectron atoms than in the hydrogen atom - all energy states associated with forces of attraction are negative. Because the attractive force between the nucleus & an electron in any orbital increases with increasing nuclear charge, the orbital energy becomes more negative (lower) as the atomic number increases- thus, the energies 1s, 2s, 3s, & 4s orbitals are lower in all multielectron atoms than in the hydrogen atom. In a multielectron atom, the various subshells of a principal shell at different energy levels, but all orbitals within a subshell are at the same energy level . One way to think about the repulsive forces between electron atom is that all the electrons located between a given electron & the nucleus screen , or shield , that electron from the full attractive force of the nucleus- the effectiveness of the shielding depends on the orbitals in which the shielding electrons & the shielded electron are found. An s electron from any principal shell has some probability of being found near the nucleus- we say that an s electron penetrates through inner-shell electron to approach the nucleus. In contrast, the 2 lobes of a p orbital are separated by a nodal plane through the nucleus, at which point the electron probability falls to zero. A p electron is less penetrating than an s electron & the electrons in d and f orbitals are less penetrating still. Highly penetrating electrons are less effectively shielded by inner-shell electrons, are more strongly attracted to the nucleus, & are at lower energies than less penetrating energies- the increasing order of subshell energies is: s < p < d< f . o E.g. the 3 p orbitals are degenerate (at the same energy level); likewise, the 5 3d orbitals are degenerate- they all have the same energy, but the energy of the 3d orbitals is higher than that of the 3p orbitals. In relation to quantum numbers, orbital energy is determined primarily by n : The lower the value of n , the lower the value of l , the lower the orbital energy- the orbital energy doesn’t depend on the value of m l .
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In higher-numbered principal shells of a multielectron atom, some subshells of different principal shells have nearly identical energies.
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Gen. Chem.- Chapter 8 - Chapter 8 Electron Configurations...

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