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Oddo-Harkins rule Rule stating that the cosmic abundance of elements with an even atomic number is greater than that of adjacent elements with an odd atomic number. Consequently, a graph plotting relative atomic abundance against increasing atomic number (Z) displays a 'toothed' curve, rather than a smooth line. The reason for this is connected with processes such as helium burning (see nucleosynthesis). 42He is a basic building block, and so additions produce even numbers, e.g. 42He + 42He → 84Be;84Be + 42He → 126C. AILSA ALLABY and MICHAEL ALLABY. "Oddo-Harkins rule." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 21 Mar. 2009
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What elements have such small masses that they are not even considered when atomic masses are calculated?
Electrons
Why could you use clues about atomic mass to place elements even though the table is now based on atomic number?
the bigger the mass of an element, the higher its atomic number.
Why is the atomic mass not a nice even number?
Because most elements that have at least one isotope stable against radioactive decay have more than one such isotope. The individual isotopes have integer mass numbers, but the naturally occurring abundances of the various isotopes do not usually have any integral ratios to one another, and the atomic mass is a weighted average of the isotope masses.
Can atoms of two different elements have the same atomic number and could they have the same mass number?
The atomic number, or Proton number, defines which element it is. So by definition, two different elements must have a different atomic number, or else they'd be the same element. Atomic mass is the number of protons + neutrons in the element's nucleus. Since the number of neutrons in the nucleus can vary, even within a single element (as isotopes) it is possible to have one isotope of one element sharing an atomic mass with an isotope of another element.
Is there an atom with an atomic mass of 200?
Yes. There's even a stable atom with an atomic mass of 200 (well, not QUITE 200): Mercury has a stable isotope with a mass of 199.9683. Several other elements (platinum, gold, lead, etc.) have isotopes with atomic mass near 200, but they're all radioactive.
What elements have such small masses that they are not even considered when atomic masses are calculated?
Electrons
How does mendeleevs periodic table differ from moselys periodic table?
Mendeleev's Periodic Table was different from Moseley's in that Mendeleev arranged the elements inÊthe table according to atomic masses while Mosley's periodic table was arranged accordingÊto atomic numbers that were increasing.ÊÊThe modern periodic table used today is based on the Moseley model.
How can specific elements be identified in the periodic chart?
element symbols, atomic number and atomic mass, or even color on some tables.
What element is the lightest of the elements?
Hydrogen is the lightest of all elements. According to the Periodic Table, its atomic weight is 1.00794 u, even lighter than helium.
What is the name of the two numbers assigned to every element on the periodic table?
Atomic number (protons) and atomic mass (not to be confused with atomic weight, even if the difference is slight)
Why odd atomic number elements have 2 isotopes?
I don't know where you got the notion that elements of odd atomic numbers have two isotopes, but we don't have to look far for a counterexample: hydrogen... atomic number 1... has not one, not two, but THREE isotopes that exist for meaningful lengths of time. If you mean STABLE isotopes, then we have to go a bit further: the first four elements of odd atomic number (hydrogen, lithium, boron, nitrogen) do in fact have two stable isotopes. However, at the fifth we find our counterexample: fluorine (atomic number 9) has only one stable isotope, fluorine-19. Furthermore, helium (atomic number 2) ALSO has two stable isotopes, so we can't even invert the original question and ask why EVEN atomic number elements DO NOT have two isotopes. The question is therefore meaningless, as it's asking for an explanation of something that does not, in fact, actually happen.
Is the lightest of all the elements?
Hydrogen is the lightest of all elements. According to the Periodic Table, its atomic weight is 1.00794 u, even lighter than helium.
Can an atom of two different elements have the same mass number?
Yes. The mass number is basic to the different elements, even more useful than the atomic number. (Unless it is an isotope. Isotopes have a different amount of neutrons than the basic element atom which makes a difference in mass number too. So, a difference in mass numbers doesn't always mean it is a different element.)
Why zero group elements are mono atomic?
Atoms of these elements do not combine with other atoms, even atoms of the same element, because their valence electron shells are full.
Do all elements have the same atomic weight?
No they are all different and even some atoms of the same element have different weights
How atomic mass related isotope?
It isn't, as such. Isotopes of the same element have different numbers of neutrons, and neutrons have a mas of one Atomic Mass unit (amu). So isotopes have different atomic masses, but being told the number of neutrons any isotope has, will not enable you to say what element or atomic mass it had, unless you remembered the details for every single isotope. Even then different elements can have the same number of neutrons. Isotopes do get named after their atomic mass however - uranaium 235 has an atomic mass of 235, for instance.
Are undefined numbers real numbers?
By its very name .. it is UNDEFINED. Even in the Extended Real Number set containing +-infinity these elements are UNDEFINED.
