Atomic Masses

[Fellowes]

What do the brackets represent on the atomic masses on the periodic table?

 

Whats the relationship between the elements 110 through 114 on the periodic table?

[JaKiri]

The atomic masses on the periodic table are the average masses of the isotopes that occur naturally, in the ratio that they occur. The ones in brackets do not occur naturally, so you can't calculate the similar value.

[ed84c]

I belive the ones that have a decimal are ones where there is the average isotopical mass, done like a histogram average (i.e. also incorperating how often each isotope occurs)

[jdurg]

Yeah, the brackets pretty much mean 'this element doesn't occur naturally, but the weight we have here in the brackets is for the isotope that's easiest to make'. The weights of the other elements are calculated based on isotope percentages as mentioned earlier. Scientists will take purified samples of elements and run them through a mass spec. They are then able to see the different isotopes and their masses. With that information they can calculate the atomic weights. As the instrumentation and sample sizes increase, the weights become even more accurate.

[swansont]

I think the bracket refers to the atomic mass number of the longest-lived isotope, which may or may not be easiest to make.

[Fellowes]

Understood, but what do elements 110 through 114 have on the periodic table? I weas just wondering about this one (110 - 114) because my science teacher says that sometimes periodic tables dont have those elements? And their names are really close to being the same, whats the relation?

[swansont]

Understood, but what do elements 110 through 114 have on the periodic table? I weas just wondering about this one (110 - 114) because my science teacher says that sometimes periodic tables dont have those elements? And their names are really close to being the same, whats the relation?

 

Was your table printed before or after 1997?

 

If it was before, the names will be generic, as they hadn't all been discovered, and of those that had, they hadn't been officially "named" when your periodic table was printed. There is some contention over who discovered what and when, and who has the right to name the elements. Russians vs the West, basically. More

 

More recently, there was some controversy over data for two isotopes (116 and 118), and the paper supporting the discovery was withdrawn after it was shown the data were fabricated.

[jdurg]

The 'temporary' names given are assigned by IUPAC. Until a formal name is decided upon, they use a systemic latin system. For element 115, for example, they would use Ununpentium (115-ium in Latin). So this is why many of those elements appear to have similar names, however the temporary naming does make sense. I remember when I first started chemistry back in the mid-90's, a VAST majority of the elements past the actinides had these temporary names. Kind of makes me feel old seeing these official names coming out.

[Ophiolite]

I remember when I first started chemistry back in the mid-90's, a VAST majority of the elements past the actinides had these temporary names. Kind of makes me feel old seeing these official names coming out.

I saw my first periodic table in 1960. Imagine how I feel.

[swansont]

I saw my first periodic table in 1960. Imagine how I feel.

 

Was that when the atomic mass was defined using O-16, rather than C-12? I forget when they made the switchover. I've seen tables based on the old standard.

[budullewraagh]

isnt the mass of carbon 12.00111 based on the carbon=12 scale?

[Ophiolite]

Was that when the atomic mass was defined using O-16, rather than C-12? I forget when they made the switchover. I've seen tables based on the old standard.

I believe you are right. If I strain hard enough I can dimly recall the head chemistry teacher (called Gleamo, for his blindingly white lab coat) telling us of the new standard. If I'm recalling correctly it would have been '61 or '62.

 

Just checked before posting. It was '61. Apparently till the mid 1800s it was H=1. (That one's from a website, not memory.)

[Fellowes]

haha i see, interesting, we're not very far in chemiostry yet but we're getting through the basics, rightnow we're on structure and 'physics'

[budullewraagh]

physics and chemistry overlap significantly when you get to the more advanced realms of both

[jdurg]

physics and chemistry overlap significantly when you get to the more advanced realms of both

 

 

Yeah, that's a ugly little course called 'Physical Chemistry'. <cowers in the corner in fear>.

[budullewraagh]

aww, that's the best stuff though...even though i have yet to find a good source for phys chem info. i love things involving phys chem and structure. if i were around at the time i would have beaten watson and crick to figure out the double helical structure

[JaKiri]

isnt the mass of carbon 12.00111 based on the carbon=12 scale?

 

Carbon 12 = 12. For C as a whole, you have to take the other isotopes into consideration.

[budullewraagh]

of course. you obtain the atomic mass by adding the products of all of the isotope masses and their natural percent abundancy

[5614]

of course. you obtain the atomic mass by adding the products of all of the isotope masses and their natural percent abundancy

 

yes, it's the weighted mean.

[Tetrahedrite]

isnt the mass of carbon 12.00111 based on the carbon=12 scale?

Too many zeros, average atomic mass = 12.011g/mol