How can I identify atom from element? Also question about isotopes?!?

The periodic table is officially called: Periodic Table of the Elements.
Therefore the periodic table is a table of all the known elements. It does not illustrate any atoms.

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.

You say: .For example, the symbol H (that is in the periodic table) means hydrogen atom, the symbol Rn (also in the periodic table) stands for radon, and the symbol Na is used for a sodium atom."
NO – that is not correct: H in the periodic table represents the element hydrogen , Rn represents the element radon and Na represents the element sodium.

Your second paragraph:
All elements in the periodic table exist as isotopes. On the periodic table, dealing with carbon – the symbol is only C meaning the element carbon ( The periodic table does not show C12) If you look at the published relative atomic mass for the element carbon on the periodic table you will see this as 12.011. This is the weighted average atomic mass of all the isotopes in which carbon exists. All atoms of the element carbon have 6 protons. This is what defines the atom as carbon. A very high percentage of natural carbon atoms contains 6 neutrons – but there are other isotopes that contain 7, 8 or more neutrons. This is why yje relative atomic mass of natural carbon is not exactly 12.000 .
I suggest that you go to :
http://www.chemicalelements.com/elements/c.html
This is a detailed periodic table that gives all the data on all the isotopes of every element . Click on the element in the table and the full details of the element will be given

I see we have a few differences of opinions.. here's mine

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first.. let's define an atom.
.. "an atom is a tiny particle of matter consisting of a nucleus which contains
.. .at least 1 proton surrounded by a field of electrons. That nucleus MAY
.. .contain 1 more neutrons,"

looks something like this
https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Helium_atom_QM.svg/1920px-Helium_atom_QM.svg.png
the blue and red spheres represent protons and neutrons.

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now.. imagine this. Imagine you raided your grandmothers pantry and collected a couple of hundred perfectly clean mason jars. and you lined them all up on your lab bench. Then you took a sharpie and wrote on one jar.
.. "atoms with 1 proton"
and on a different jar
.. "atoms with 2 protons"
and on a different jar
.. "atoms with 3 protons"
.. etc
until all the jars were labeled

now image you have a super powerful microscope. So powerful you could see individual atoms. So powerful that you could actually see inside each atom and see the nucleus. And so powerful that you could actually count protons.

now imagine you have a super sharp pair of tweezers. So sharp that you could pick up a single atom.

now imagine you have a huge pile of atoms. All different shapes and sizes. And you have an infinite amount of time on your hands....

And you start sorting.
.. into the jar labeled "atoms with 1 proton".. ..go all the atoms with 1 proton
.. into the jar labeled "atoms with 2 protons".. go all the atoms with exactly 2 protons
......
.. into the jar labeled "atoms with 92 protons".. go all the atoms with exactly 92 protons

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when you're done sorting, you think to yourself.. "self. atoms with x protons is just too long and too impersonal. I'm going to give these jars better names"
.. and you write on the jar of atoms with exactly 1 proton... "hydrogen"
.. and you write on the jar of atoms with exaclty 2 protons.. "helium"
.. etc
.. and you write on the jar of atoms with exactly 92 protons.. "uranium"
...etc
until all the jars are renamed.

**********
now you start inspecting each jar and you notice something unusual. Although all the atoms have the same number of protons in any jar, they have different numbers of neutrons. The all react chemically about the same. But they have different masses and different stabilities. So you decide you need a naming system to identify atoms in the same jar that have different numbers of neutrons... and you come up with the term.. "ISOTOPES". "Iso" meaning "same".. and "topes" meaning "place". They come from the "same place".. i.e.. they are in the same JAR.

AND, you do one more thing. You identify which of those atoms are stable. And you measure the mass of those atoms on a balance. And you average those masses of those stable atoms (weighted by the percent abundance of each of those stable isotopes) and you write that weighted average mass on the outside of the jar. And you call that weighted average mass... "relative atomic mass"

********
********
ATOMS are those individual particles
ELEMENTS are the mason jars
ISOTOPES are atoms with the same number of protons.. with different numbers of neutrons

the PERIODIC TABLE shows the mason jars, and the number of protons in each atom in that jar (the atomic number) and the weighted average mass of the stable atoms of any given element (unless it's shown in parenthesis which means there are no stable isotopes of that element and the atomic mass of the most stable element is shown in the parenthesis).

********
let's look at a couple of examples.
.. dig out a periodic table
.. find copper
note the following
.. atomic # = 29... meaning.. ALL copper atoms have exactly 29 protons AND ALL
.. ... ... .. ... .. .. .. ... . .. .. ...atoms with exactly 29 protons are atoms of copper
.. atomic mass = 63.546.. this is the WEIGHTED AVERAGE atomic mass.. NOT
.. ... ... .... .. ... ... ... ... .. .the mass of any 1 atom of copper

now look at this page
https://en.wikipedia.org/wiki/Isotopes_of_copper
note
.. (1) the "Z(p)" column = atomic number = 29... this is the number of protons
.. (2) the "N(n)" column ranges from 23 to 51. This is the number of neutrons
.. (3) each row is a different "isotope" of copper. Each row has a different # of neutrons
.. (4) the two that say "stable". Those are the stable atoms used to calculate avg
... .... ... ... .. .. .. ... ... .. .. .. .. . .atomic mass... that number on a periodic table.

the average atomic mass is calculated like this
.. (62.9295975 x 0.6915) + (64.9277895 x 0.3085) = 63.546

notice the "nuclide symbol" column you see this
.. 52 Cu
.. 53 Cu
.. 54 Cu
.. 55 Cu
...etc
those numbers are called "mass numbers" and they are the sum of protons + neutrons. Z(n) + N(n). Those "mass numbers" are not really a mass, but a count of nucleons (protons and neutrons are nucleons). Mass numbers are NOT shown on a periodic table.

one last thing to note. You can see there are 29 different isotopes (rows) shown in that link. Each with a different number of neutrons. Those are the "discovered".. (i.e.. isolated in a lab somewhere).. isotopes of copper. But... because we grouped our atoms into elements by the number of PROTONS.. and didn't specify any limits on NEUTRONS, there are an infinite number of isotopes of any given element

an atom with
.. 29 protons and 0 neutrons... is Cu-29... an "undiscovered" isotope of copper
.. 29 protons and 1 neutron... . is Cu-30... an "undiscovered" isotope of copper
.. 29 protons and 2 neutrons. . is Cu-31... an "undiscovered" isotope of copper
.. 29 protons and 3 neutrons. . is Cu-32... an "undiscovered" isotope of copper
... etc
.. 29 protons and 34 neutrons. is Cu-63... a discovered and stable isotope of copper
.. etc
.. 29 protons and ∞ neutrons... is Cu-∞.... an "undiscovered" isotope of copper
.. etc

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********
back to your question.
.. (1) C-12 is the isotope of carbon containing 6 protons + 6 neutrons.
.. . ...how do I know that? ALL carbon atoms are in that jar labeled
.. .. ..atoms with 6 protons. Look at carbon on a periodic table. atomic number = 6
.. .. ..The "12" in C-12 is the "mass number" = # protons + # neutrons.
.. . ....so... 12 = 6 + # neutrons ..====> # neutrons = 6
.. (2) the periodic table does NOT list single atoms. It's gives the name of
.. .. ..the "jar", the # of protons of atoms in that jar, and the average mass
.. .. .of stable atoms of that particle element.

one last thing. the reason we use weighted average atomic mass is because that's what is typically found in the lab. If we take a sample of uranium off the shelf, it's going to be 99.2742% U-238 and 0.7204% 235. So we use the weighted average mass 238.0289 in our calculations instead of the mass of U238 or U235. You'll figure that out as you go deeper into chemistry.

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questions?

Atom is very simple =
atomic mass = no. of protons + neutrons
Atomic no. = no. of protons

We all learn this in class 6

Now isotopes .........
First understand that the periodic table only gives the molar mass of the most common isotope.
Its very simple.U know from above that no. of protons = molar mass. Well in all isotopes of a same element the no. of protons is same but the no. of neutrons is different in different isotopes.Like : Oxygen 16 has 8 protons and 8 neutrons while Oxygen 17 has 8 protons and 9 neutrons.
Example :
If element X has 14 protons and 12 neutrons what is element X and what is its isotope ?

Atomic mass = protons+ neutrons = 26
First no. of protons = atomic no.
14= 14th element (silicon)
Silicon -28 is most common isotope in earth bcoz its not radioactive and no. of protons = no. of neutrons
Now find isotope of that element
= 14+12=26 (26Si)

Hope it helps,
Unknown

An atom is a single 'piece' of an element. Put another way, an element is composed of one (and only one) type of atoms. It is possible to use those two words interchangeably but, generally, elements means a collection of atoms.

The type of atom, or element, is determined by the number of protons that the atom has. An isotope means that the atom has the same number of protons but a different number of neutrons in the core. For example, C12 is the isotope of C with 6 protons and 6 neutrons while C14 has 6 protons and 8 neutrons. Chemically there are the same but they have slightly different masses.

an atom is just the basic unit of all matter.
an element is a substance that can no more be simplified or broken down.
hope I helped! xx

I think the atom is sorta a round shape dude.