1. The mass spectrum can be observed for all forms: pos. ion, neg.ion, molecules, and atoms, can't it?

2. Is there a formular to calculate how many spectrum of the substances we need to observe? Please give me some examples, and calculation.

3. I knew the examples of H2S+, and how to draw the table to find the peak, but I don't know the formula to calculate how many peak without using the table, so I need other examples, and how to calculate peaks.

Thanks a lot

1. A mass spectromter analyzes ions, or ions formed when a neutral atom or molecule is ionized and broken up before entering the mass analyzer. Since you are analyzing fragments of an original molecuile, it is often difficult to say what the original molecule was. It might have been a different molecule that produces the same ionic fragments.

2. The short answer is no, except that the OPTICAL spectra of one-electron atoms (hydrogen) and ions can be easily calculated. Are you talking about mass spectra or optical spectra?

I am not clear why you ask how many spectra you NEED TO observe. In order to do what? Is this a lab assignment?

3. I have no idea what kind of spectra you are talking about here

Thank you drwls

i am reviewing my chemistry and doing the problems from my textbook. Because my teacher did not have the lecture about this part, so I am reading my text book and trying to solve problems. My textbook only have two problems of this theory:

1/ find how many peaks you would observe in the mass spectrum of the positive ion of CF4^+.( C has 2 stable isotopes, F has 1 isotope)
and
2/ Hydrogen has two isotope H1 and H2, and Sulfur has four isotopes S(32), S(33) S (34) and S (35). How many peaks you observed in the mass spectrum of positive ion H2S+

I solved these problems and and checked my answer with the answer key, but I still don't understand a lot. I would like you to explain for me what the optical spectra and mass spectra are,and the difference between them as well as some other examples, please.

Optical spectra are the wavelengths at which an element or compound emit and absorb light or infrared radiation. That subject used to be a specialty of mine.

Your questions are apparently concerned with mass spectra, not optical spectra. A mass spectrum shows the different charge-to-mass ratios of ions that pass through a device that separate them, based upon the value of that ratio.

Ions for which different elements have different isotopes will exhibit more than one "mass" peak for each ion. The spectrum looks like a series of "peaks" or "spikes" of different intensity. The strongest ones will correspond to the most abundant mass values.

1. CF4+ will have two possible masses (in amu units) of 12 + 4*19 = 88 or 13 + 4*19 = 89. The 88 peak will be about 99 times higher because C12 is 99 times more abumndant than C13.

2. H2S can have three possible mass values for the H2 part (1+1 = 2, 1+2 = 3, or 2+2 = 4) and 4 possible values for the S atom (32, 33, 34 or 35). The number of possible masses of the combined H2S+ ion are:
2+32 = 34
2+33 OR 3+32= 35
2+34 OR 3+33 OR 4+34 = 36
2+35 OR 3+34 OR 4+33 = 37
3+35 OR 4+34 = 38
4+35 = 39
That is a total of 6 possible lines.

Just construct a table with all the possible mass combinations, and count them, as I did above. There is probably a formula one could write, but it will differ depending upon what the different possible isotope mass values are, and how many atoms of each type there are in the molecular ion.

Thank you so much drwls

I'm very pleased with this question and answer because it answered one of my assignment question.

Thank you very much Bun and Drwls

1. Yes, mass spectrometry allows the observation of mass spectra for various forms, including positive ions, negative ions, molecules, and atoms.

2. There isn't a universal formula to calculate how many spectra of substances we need to observe because it depends on several factors such as the complexity of the sample and the specific information required. However, I can provide you with some examples that might help clarify the calculation process.

Example 1: Let's say you have a mixture of three different compounds. To obtain individual spectra for each compound, you would need to analyze the mixture three times, each time focusing on one compound while ensuring the other compounds are not present or do not interfere.

Example 2: If you are interested in studying the fragmentation pattern or isotopic distribution of a single compound, you need to conduct one analysis. However, you might need to measure it under different conditions (varying collision energies or ionization methods) to obtain additional spectra.

In summary, the number of spectra required depends on the specific objectives and research questions.

3. To calculate the number of peaks in a mass spectrum without using a table, you need to consider the molecular formula of the compound and the presence of isotopes. Each element typically has multiple isotopes with different masses. The formula to calculate the number of peaks is known as the "n+1 rule" and is based on the presence of "n" atoms of a particular element.

Example: Let's consider the molecule C4H10. The carbon atom has multiple isotopes, mainly carbon-12 (mass = 12 amu) and carbon-13 (mass = 13 amu). Since there are four carbon atoms in the molecular formula, we apply the n+1 rule: 4 + 1 = 5. Therefore, there will be five peaks corresponding to the different isotopic combinations of carbon atoms.

It's important to note that this rule applies to elements that have isotopes, and it assumes that the isotopic distribution is roughly natural abundance. For complex molecules with more elements, the calculation can become more involved.

I hope this helps! If you have any further questions, feel free to ask.