How do you know how many neutrons an isotopes has if you dont know the atomic mass?
139239
you don't. to determine the neutrons you have to know the atomic number(identity) and the atomic mass. then subtract.
95148
Actually, the mass of a proton is 1.00727664669 atomic mass units.\n\nAn atomic mass unit is defined such that Carbon 12 is exactly 12.  The carbon atom weighs less than 12 times the proton (because of nuclear binding energy).
814357
one way is that the atomic number is the same as the number of protons and the other way is to subtract the neutron by the mass
33642
Use the periodic table to find the atomic mass of the element and subtract from this the atomic number.  \n\nThe atomic mass is equal to sum of proton and neutrons, and the atomic number is the number of protons an atom has.  Electrons have such a small mass that they don't really have any noticable effect on the atomic mass.\n\nEx: Oxygen (atomic mass - 16, atomic number - 8)\n\n16 - 8 = 8, therefore the number of protons is equal to 8
773257
Re:  For Helium, the "2" is called the atomic number and it means that Helium has 2, protons, 2 nuetrons and 2 electrons.\n\nFor Lawrencium (Lr) it should show 103 as its atomic number.  That means that Lr has 103 protons, 103 neutrons and 103 electrons.  \n\nThe 2, 8, 18, 32, 32, 8, 3 numbers are showing electrons per shell (different subject) but you'll see that if you added all the numbers 2+ 8+ 18+ 32+ 32+ 8+ 3 = 103.  103 is the total number of electrons Lr has.   \n\n____________________________________________\n\n\n\n\nFor a Normal Neutral Atom, the number of protons (p+), neutrons (n) and electrons (e-) are all the same. \n\nJust look up the atomic number from the periodic table to determine them.\n\nFor example:\n\nC: 6p, 6n, and 6e-.\nN: 7p, 7n, and 7e-.\nK: 19p, 19n, and 19e-.\n\nNow, Determine the number of p, n, and e- for Ca.\n\n\n\n\n\n\nIf you guessed, 20p, 20n, and 20e-, you are Correct!\n\n\nNote that, if you add the number of the atom's p and n you will get the Mass number (Z). \n\nThe periodic table shows Z of calcium as 40.078 because 20p + 20n = 40 (amu) \n\nAnother Example: Oxygen, having atomic number of 8, will have:\n8p, 8n, and 8e-. This means that Oxygen will have the mass number of 16 because; p + n = Mass number (Z).\n\n______________________________...\n\nFor Isotopes:\nIsotopes are atoms that have same number of protons but different number of neutrons.\n\nYou've already seen that normal Carbon has: 6p, 6n, and 6e-.\n\nThis normal carbon is called "Carbon-12". The "12" denotes its Mass number (Z). Which is p + n.\n\nThere are isotopes of Carbons and one of them are Carbon-13. Since you already know that Carbon must have 6p, Carbon-13 has 7n. 13 - 6 = 7. The number of the electrons are still the same as number of proton. \n\nIn another words, simply subtract the number of protons from mass number to determine the number of neutrons.\n\nNow, determine the number of p, n and e- of Fluorine-19:\n\n\n\n\n\nIf you guessed 9p, 10n, and 9e-, you are Correct!\n\n______________________________...\n\nFinally, there are ions. Ions means that an atom has either gained or lost electrons. Keep in mind that eletrons are NEGATIVE in nature (e-) and when an atom Gains e-, it becomes More negative.\n\nFor example: Fluoride ion, F- means that it has GAINED one electron compared to its neutral F state. Therefore;\n\nF has 9p, 9n, and 9e-, But F- has 9p, 9n, and TEN e-.\n\nO has 8p, 8n, and 8e-, But O2- has 8p, 8n and TEN e-, because O2- means that it has Gained 2 more electrons than its normal O state. \n\nNow, determine the p, n and e- for P3-.\n\n\n\n\n\nIf you guessed 15p, 15n, and 18e- you are Correct!\n\nFor atoms that have positive charges (cation), remember that they LOSE e- to become positive. So, Li+ has 3p, 3n and 2e-. \n______________________________...\n\nKeep in mind that you need to know how to combine all three of the ideas mentioned above. For example, you may be requested to determine the p, n and e- of Magnesium-25 ion. \nYou need to know that since Magnesium is in Group IIA, it will turn into 2+ ion. Therefore Magnesium-25 ion will have 12p, 13n, and 10e-. \n\nI hope this answers your question. Good luck!
786060
First you need to look up the element on a periodic table of elements.  I am sure you have one laying around somewhere =P\nAnyway, then look in the square that contains your element for a number either in the upper left corner or in some cases directly above it.  That is the number of protons in the atom.  Then you also know the number of electrons which is exactly the same as the number of protons.  To figure out neutrons, look for another number on in the square that isnt in the left corner or above the element.  This is the atomic mass.  Take the atomic mass and subtract the number of protons to get the number of neutrons
972738
The number of protons is equal to the number of electrons (unless it is an ion), but in this case they are equal. The atomic number is equal to the number of protons, and the mass number is the number of protons plus the number of neutrons.
844991
Potassium is number 19. That means it has 19 protons. If it is an atom and not an ion, it has the same nimber of electrons as protons. Since protons are positive + and electrons are negative - , they have to balance. You find the neutrons by subtracting the atomic number from the atomic mass, since both the protons and neutrons weigh 1 and make up the mass. The electrons in the energy levels can move to another atom in compound formation.(ions)
664696
The atomic number is equal to the number of electrons in the atom - therefore there are 28.However, since you have a postive 3 charge, there must only be 25.\nNow normally, the number of electrons would equal the number of protons, but since you have a charge of +3, that means that there are three less electrons than protons(you don't lose protons until you get into radioactivity, and it doesn't soung like you're there yet), so that means that you have 25 electrons and 28 protons.\nThe atomic mass is defined as the number of protons + the number of neutrons, so you have 60 = 28 + (number of neutrons). Therefore, you have 32 neutrons. Good Luck!
974033
Atomic number always says how many protons.  Every element will always be defined by its unique number of protons.  Atomic number 5 will have 5 protons.  Electrons don't really weigh anything, so they don't count towards mass number.  So what's left? Neutrons.  So 10mass units-5for protons=5 neutrons (A)\n\nThe number of electrons in a neutral atom must cancel the charge of the protons.  Each proton is +1  and each electron is -1.  If I have 5 protons in the nucleus, I have +5.  A neutral atom should have 0 charge.  So 0=+5-(# of electrons) and you get 5 electrons (A)
1138448
Look on a periodic table.\n\nIt should be listed below the atomic number as a decimal value.  The mass number is an average mass (in atomic mass units) of an element, based on different isotopes.  It equals the number of protons + the number of neutrons in the nucleus.
924159
It depends on what you have, if you know the mole of the molecule, you can determine the mass by converting molar mass (g/mol) into mass (g). The mole of the molecule can be found on the periodic table, but first you need to know the molecule formula of the compound. Then add it up.
843112
Do a search for the isotopes of gold.  The list should give you each of the isotopes with its "mass number" (there are about 35 isotopes beginning with Au-172 and going through Au-205. ) The mass number is the total number of protons + neutrons.  Since gold is element #79 all of its isotopes have 79 protons so just subtract 79 from the mass numbers to get the neutrons.  Assuming we are talking about neutral gold atoms, the electrons = protons = 79.
263751
The mass of protons and neutrons are nearly identical, the mass of an electron is about 1/1840th the mass of a proton, thus it is negligible, so you can't really tell its there.
703218
A compound has a formula that tells us exactly how many of each kind of atoms a compound has. That compound is the same all over the world. \n\nOne exception to this may be if a different isotope of an atom was used. An isotope has the same number of protons but a different number of neutrons. So the mass would be slightly different.
326489
It depends on which isotope you are atlking about.  The number of the isotope gives you the total number of nucleons (protons and neutrons) that it has.  Potasium is element number 19, so it has 19 protons (it is electrically neutral so it has just as many electrons as protons).  To find the number of neutrons just subtract 19 from the total number of nucleons.\n\nPotassium-39 has 20 neutrons, 19 protons and 19 electrons\nPotassium-40 has 21 neutrons, 19 protons and 19 electrons\nPotassium-41 has 22 neutrons, 19 protons and 19 electrons
884412
There are two stable isotopes. Mg-24 has 12 neutrons, while Mg-26 has 14 neutrons.