Chapter6,II

# Chapter6,II - Chem 200 Dr Saidane Lecture Notes Chapter 6...

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Chem 200 Dr. Saidane Lecture Notes Chapter 6, Part 2 Models of Atoms Atomic Orbitals In classical mechanics we speak of the path of electrons called orbits. However, because of the wavelike properties of electrons we cannot say that an electron will be found at a certain point in an atom. Ernest Shrödinger, an Austrian scientist, devised an equation that describes electrons in terms of quantum mechanics. This equation lets us calculate the probability that an electron is at a particular point in space, called orbital . Each atomic orbital corresponds to an energy level of the electron. The higher the energy, the larger the orbital. The various shapes of atomic orbitals can be classified into four main types, which are labeled s , p , d , and f . There are many orbitals of each type. They differ principally in the size of the cloud, which is related to the energy level. The simplest way of drawing an atomic orbital is as a boundary surface, a surface within which there is a high probability (typically 90%) of finding an electron. An s -orbital has a spherical boundary surface , because the electron cloud is spherical. s -orbitals with higher energies have spherical boundary surfaces of bigger diameter. A p -orbital is a cloud with two lobes on opposite sides of the nucleus . The nucleus lies on the plane that divides the two lobes, and an electron will, in fact never be found at the nucleus itself if it is in a p -orbital. There are three p -orbitals of a given energy, and they lie along three perpendicular axes. The boundary surface of a d -orbital is more complicated than that of an s - or p - orbital. There are five d -orbitals of a given energy; four of them have four lobes, one is slightly different and is oriented along an axis . In each case an electron that occupies a d -orbital will not be found at the nucleus. The f -orbitals have more complicated shapes. There are seven f -orbitals of a given energy . The shapes of the f-orbitals are rarely needed to explain chemical properties and therefore will not be studied here.

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Quantum Numbers and Atomic Orbitals Shrödinger found that each atomic orbital is identified by three numbers called quantum numbers . One quantum number is called the principal quantum number, n ; the other two are the azimuthal quantum number, l , and the magnetic quantum number, m l . These quantum numbers have another job: as well as labeling the orbital, they tell us about the properties of the electron that occupies a given orbital.
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