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# 請問有關material engineering

1. list eight commonly encountered engineering materials

2. list some materials usage changes that you have observed over a period of time in some manufactured products. what reasons can you givefor the changes that have occured?

3. what factors might cause materials usage predicitons to be incorrect?

4.要怎麼樣 ion的spdf 符號

eg. iron(Z=26): (1s^2)(2s^2)(2p^6)(3s^2)(3p^6)(3d^6)(4s^2)

這些數字是怎麼來的阿

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### 1 Answer

- 2 decades agoFavorite Answer
1. alloy, steel, silicon, aluminum, copper, zinc, titanium & iron

2. in the early 90', it was a rare event to see a bicycle made of something other than tube steel. as time progressed, composite wheels have become morepopular because the development in technology make these kind of material more affordable.

3. the development of new material processing technology or the new material might reduce or alter the cost of a given material

4.Z represents the number of electrons around the nucleus, so for iron, there are 26 electrons spinning around the nucleus. These electrons reside in "shells", referred to as eneregy levels. For our purposes, we onsider 4 energy levels, each referred to as the Prinicpal Quantum numbers, abberviated by the letter 'n'. Each energy level has a corresponding number of sub-energy levels, so the first energy level (n=1) has one sub-level, the second (n=2) has 2 and so on. There are 4 types of sub-levels: 's','p','d' and 'f''. Each sub-level has different orientations for electrons to reside. s has 1 orientation, p has 3, d has 5 and f has 7 orientations. Each orientation has a maximum of 2 electrons which spin in opposite directions (because of their same charge) in the same sub-level. So, when assigning electrons to the energy levels, the basic from is (1s^x)(2s^x)(2p^x)(3s^x)(3p^x)(3d^x)(4s^x)(4p^x)(4d^x)(4f^x). The number of energy levels increase as you go down the rows of the periodic table; so row 1 elements have 1 shell, row 2 have 2 mains shells, row 3 elements have 3 main shells, row 4 has 4 etc. The periodic table I've attached should help with this.

x refers to the number of electrons you have on that shell. So, for iron if you add up the subscripts for all the shells in the spdf notation, they add up to 26. I'm attaching a table that gives you this information; it's easier to see that way...hope it helps. Just remember, the spdf form is basically ('n'sub-level^x), where n refers to the electron shell or main energy level, sub-level is the sub-energy level and the superscrip, x is the number of electrons in that sub-level. So, for Fe^2+, you've lost 2 electrons to make a positively charge ion, therefore you have 24 electrons now. Arranging this in spdf notation gives you (1s^2)(2s^2)(2p^6)(3s^2)(3p^6)(3d^6). OK, one last thing, you can write the spdf notation in pseudo-noble gas notation, where you can write, for instance, the Fe configuration as [Ar](3d^6)(4s^2) and so on.