# Chemistry questions

dnt

## Homework Statement

1) how do you know if a double replacement reaction occurs or not?

2) how do you predict products in decomposition and synthesis reactions?

3) do you include metals in net ionic equations?

4) are the exceptions to electron configurations limited to only Cu and Cr or all elements in those groups?

5) how do you determine how many electrons are in each energy level of an element?

n/a

## The Attempt at a Solution

1) how do you know if a double replacement reaction occurs or not?

I know in a single replacement you simply look at the activity series - if the replacing element is higher than the one it wants to replace, you have a reaction. if its lower, you dont.

however, how do you use the activity series (or any other information) to determine whether a double replacement reaction will occur?

2) how do you predict products in decomposition and synthesis reactions?

sometimes its easy (eg, 2 H20 -> 2 H2 + O2) but sometimes its more complicated (eg, Mg(OH)2 -> ??). what are the rules to use? how do you konw how far to break a compound down to?

3) do you include metals in net ionic equations?

my guess is yes because they are not ionic and thus do not dissolve into solution. is this correct reasoning?

4) are the exceptions to electron configurations limited to only Cu and Cr or all elements in those groups?

i understand that copper and chromium are exceptions to electron configurations because the electrons would rather be in the 3d orbital than the 4s orbital (for energy reasons i think) but does this "rule" work all the way down their respective groups among transition metals?

eg, for Mo: would it be [Kr] 5s1 4d5?

5) how do you determine how many electrons are in each energy level of an element?

eg, for Zn: i know there are 2 e in the first energy level, then 8 in the 2nd, but after that does it go 18 (because in 3 there is 3s2, 3p6 and 3d10). i thought the max # of electrons in any energy level are 8?

im trying to distinguish between energy levels, orbitals and how you actually draw them out ("shell structure" with the nucleus, rings, electrons, etc). am i doing this correctly?

thanks for any help!

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dnt
anyone? a little help?

thanks.

Staff Emeritus
Gold Member
Could you please tell us what level this is at? Also, have you written down the questions in EXACTLY the same words as they were given to you?

The questions themselves appear as though they are expecting oversimplifications for answers (this is more forgiveable at a lower level) and/or are ambiguously/poorly written.

Homework Helper
Gold Member
1) How do you determine if a (double replacement) reaction occurs or not. (See Gibbs Free Energy Principle or Google "Double replacement reaction")

2) See above.

3) Look up the definition of "metal". Can a metal be an ion? Does the metal participate in the reaction?

4) Review Electron Configuration. Look up definition of "exception". Do copper and chromium have electron configurations or are they an "exception"? What kind of question is this?

5) Review Aufbau Principle

Be careful with your nomenclature. Are energy levels the same as orbitals, for example? Don't confuse rows (the number prefix to 3s 3p 3d) with energy levels.

dnt
Could you please tell us what level this is at? Also, have you written down the questions in EXACTLY the same words as they were given to you?

The questions themselves appear as though they are expecting oversimplifications for answers (this is more forgiveable at a lower level) and/or are ambiguously/poorly written.

I didnt write them down from anywhere - I am just asking general questions to learn more about them and have a better understanding of the material. this isn't homework or due or anything.

and its for high school chemistry.

sorry if they are written poorly. like i said I am trying to understand them better so the way i asked the questions may not make perfect sense or may be written incorrectly - i was hoping someone could clarify those parts as well. doenst need to be in too much detail but any help is much appreciated.

dnt
3) Look up the definition of "metal". Can a metal be an ion? Does the metal participate in the reaction?

a metal is not an ion (but it can be, right? eg, Mg is a metal and Mg+2 is the ion). it does participate in the reaction (eg, single replacement)

4) Review Electron Configuration. Look up definition of "exception". Do copper and chromium have electron configurations or are they an "exception"? What kind of question is this?

copper and chromium have electron configurations which are exceptions to the "normal" ways they are usually written. (at least to the best of my understanding).

normally, according to aufbau you would fill in orbitals from lowest to highest energy until they are filled, then move on. however with both copper and chromium electrons are transferred from the s orbital to a high energy d orbital - doesn't that make them exceptions?

and does that "rule" apply all the way down the groups that include copper and chromium?

5) Review Aufbau Principle

Be careful with your nomenclature. Are energy levels the same as orbitals, for example? Don't confuse rows (the number prefix to 3s 3p 3d) with energy levels.

this is where I am confused.

doesnt the number in front indicate the energy level of the orbital and electrons?

im pretty sure for any energy level there can be up to 2n^2 electrons (eg, 4th energy level can have up to 32 electrons).

but I am trying to use that information to figure out how it relates to the rings of electrons around the nucleus. and in addition how to relate that to valence electrons and outer octets of electrons. the numbers don't seem to match.

im under the assumption that if you remove all the valence electrons from any representative element you should be left with a full octet, or 8 outer electrons. but if you are at a high energy level, wouldn't you end up with more than 8 electrons if you went down to the next full level?

this is where I am confused.

(speaking of valence electrons, how do you figure them out for transition metals?)

im trying hard to get all of this so i really appreciate the help.

Homework Helper
Gold Member
The front number refers to the principal quantum number. It has been described as an energy level but that description is better applied at the suborbital level. That is where the Aufbau principle comes into play. The rule is that suborbitals with the lowest energy are filled first. This ordering does not coincide with the principal quantum number and results in the diagonal rule mnemonic.

The exceptions to this Aufbau principle (not exceptions to the electron configuration) occur for chromium and copper and others. Try searching for Aufbau rule exceptions for an explanation.

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dnt
thanks but how does that relate to the electrons per ring around the nucleus? i still cannot figure out the relationship (and how it relates to valence).