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In chemistry, valence electrons are the outermost electron s of an atom, which are important in determining how the atom reacts chemically with other atoms. Atoms with a complete (closed) shell of valence electrons (corresponding to an electron configuration s 2 p 6) tend to be chemically
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Answers:You have to look at the sub-orbitals Iron is 1s2, 2s2, 2p6, 3s2,3p6,3d6, 4s2 Now the energy difference between the 3d and 4s suborbitals is not very great (the 3d are slightly higher than the 4s which is why the 4s2 fills first) Iron (II) has no 4s electrons so is a reasonably stable configuration BUT Iron (III) has a half-filled 3d orbital (3d5) and this is ALSO a stable configuration (it has to do both with electron spins and maximising the probable distance between the electrons - but I assume you don't want a lesson in quantum mechanics) All the d-block elements (Sc, Ti, V etc up to but not including Zinc (and the ones below)) are known as transitional elements and exhibit variable valency (oxidation state) as well as forming coloured ions. The structure and properties are part of the UK A2 Chemistry syllabus. e.g. Vanadium can have an oxidation state of 5 (loses all 3d and 4s electrons), Chromium 6 and Manganese 7 In this state e.g. Potassium dichromate they can be used in many organic reactions e.g. changing alcohols to aldehydes / ketones and aldehydes to carboxylic acids. In these reactions the oxidation state is reduced down to 2 (electrons are added) and the carbon compounds are said to have been oxidised (electrons removed)
Answers:The answer depends a lot on what kind of compounds you're talking about. Most sources will tell you that Cr, for example, exists as +2 +3 and +6 ions (or, more correctly, that it exists in oxidation states of 2, 3, and 6, since no Cr(VI) compound truly contains a discrete +6 ion). Which is true if you're talking about aqueous environments at middling pHs and some oxygen. But I've made Cr compounds will oxidations states of 0 1 and 4. If you really know what you're doing, you can make something as crazy as a Zn(I) complex, but you get to publish in "Science" when you pull it off. But let's assume you're just interested in "common" oxidation states of "common" transition metals. No, there's no good way to tell, you have to just know them, or keep a periodic table handy that lists them. Many of them do stuff that you might predict based on their position in the table and electronic configuration. Ti is Gr 4, it's usually +4. Zn is Gr 12, it's usually +2. But even then, not always, because Hg is the same column as Zn, and it shows up as a +1 ion as well as +2, and most of them can be stable in multiple states. There's a pretty good table at: http://en.wikipedia.org/wiki/Transition_element Which ones do you consider common? Some ones worth remembering: V: 2,3,4,5 Cr: 2,3,6 Mn: 2,4,7 Fe: 2,3 Co: 2,3 Ni: 2 Cu: 1,2 Zn: 2 Mo and W: 2,3,4,6 Ru: 2,4; Os: 4,6,8 Rh and Ir: 1,3 Pd and Pt: 2,4 Ag: 1; Au 1,3 Hg: 1,2
Answers:1. Iodine has 7 valence electrons (it's in Group VIIA) 2. The alkaline earth elements have 2 valence electrons (Group IIA). 3. Uranium is in the f-block (the two blocks on the bottom of the periodic table). 4. Transition metals are in the d-block.
Answers:Helium is a noble gas so it doesn't give away any electrons, it has two electrons (not one). The valence of Helium is 0.