What's an atomic number?
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An atomic number is the number of protons in the nucelus of one atom of an element. This is used to identify each element as unique.
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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.
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33 (also 33 electrons and this is the atomic number too)
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Tip:  The atomic number is always the element's number of protons.
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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
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!
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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!
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94,240Pu ---> 40,93Zr + 54,144Xe + _3_ 0,1n\n\nThe first number is the proton number, the second is the nucleon number. Both of these must be conserved in fission. As the number of protons is already conserved, the difference in the nucleon number must come from free neutrons.
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Four.\n\nThe first one is usually called "n" and it gives what people think of when they say "energy level".  It's also called the "principal quantum number", I think.\n\nThe next one is usually called "l" (el) and for a given energy level, it can be anything from 0 up to "n-1".  These correspond to what people sometimes call "shells", such as the s, p, d, f, etc. shell.\n\nThe next one is called "m" and is sometimes called the "sub-shell".  Each shell can have up to "2*l+1" sub-shells.  So an "s shell" (l=0) can have 1 sub-shell.  A "p shell" (l=1) can have 2*1+1=3 sub-shells, etc.\n\nThe final quantum number is called "s" or "spin".  For each sub-shell, this can take on one of two values, +1/2 or -1/2  in some books.  This means that only two electrons are allowed in any given sub-shell.\n\nSo for n=1, the only option is l = 0, which means further that m must be 1, with 2 choices for s.  This all means that the first energy level can only hold 2 electrons.\n\nFor n=2, l can be either 0 or 1.  For l =0, m must again be 1, allowing 2 electrons.  For l = 1, m can be as much as 3, each allowed to have 2 electrons.  So adding the 2 electrons for the l=0 subshell to the 6 allowed in the 3 possible subshells for l=1 (6 electrons we get a total of 8 electrons allowed in the second energy level.\n\nYou can continue on to get totals of 18 (2 + 6 + 10) for the 3rd energy level (n=3; l =0, 1, or 2;  and m = 1, 3 and 5, each with 2 electrons allowed).\n\nThis is where the numbers that correspond to "filled energy levels" come from in the periodic table.
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Sodium has an Atomic Number of 11 and an Mass Number of 23 \n\nThis means an atom of Sodium has 11 Protons and therefore 11 electrons. \n\nSince the number of Protons + Neutrons is 23 and there are 11 Protons there must be 12 Neutrons
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Atomic number\nThis was an idea by Mossely
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"mathematician" is correct.\n\nAny atom of a given element will have the same number of protons in its nucleus.  If the atom is neutral (i.e. has no charge), then it will have the same number of electrons as protons.\nHowever, the number of neutrons in the nucleus can vary slightly from atom to atom for a given element.  Atoms of the same element but with different numbers of neutrons in their nucleus are called isotopes.  With a greater/less number of neutrons, the over all atomic weight of the atom will varry.  By taking into account the naturally occuring percentages of each of these isotopes of a given element, we can obtain the average atomic mass of all the atoms of that element.\n\nCommon isotopes you might hear would be, "Carbon-12" or "Carbon-14", these are two different isotopes of the element Carbon.  The -# after the element name indicates the total atomic mass of the atom.  Since we know that Carbon always has 6 protons, we can easily determine the number of neutrons if we know the atomic mass.
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The atomic number equals the number of protons.  Electrons should equal the number of protons, but may not if it's an ion.  Neutrons vary as to the specific isotope of the atom.\n\nExample:\nHydrogen, atomic number = 1.  Therefore, 1 proton, 1 electron.\nIt has three isotopes:\nH-1 (1 proton, 1 electron, no neutrons)\nH-2 (1 proton, 1 electron, 1 neutron)\nH-3 (1 proton, 1 electron, 2 neutrons).\n\nYou might check the section you are asking this in, though.  This is the Religion section.
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Yes, you are correct. The atomic number of Molybdenum is 42.
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Francium has 87 protons.  This information is available on the Periodic Table of Elements, the atomic number (Z) of an element is the number of protons.
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Yes an atom is the same as an element.  A single atom is the smallest particle of an element.  There are 118 different elements in the periodic table. For example, a Hydrogen atom is one proton and one electron.  The next element in the periodic table is Helium, it has one proton, one neutron and one electron.  Each of these atom examples represent their own element.  So you see a single atom does represent it's own particular element, as discussed in the Hydrogen and Helium examples.
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The atomic number tells you how many protons there are in the nucleus, and that's what identifies the element.  Subtract that number from the atomic weight and you get the number of neutrons.  Uranium has 92 protons and 143 neutrons (U235) or 146 neutrons (U238).  The different weights are called isotopes.  In an electrically neutral atom the number of electrons is the same as the number of protons.  Strip a few electrons away you get an ion (an ionized atom).  It's the structure of the electrons that strongly influences the chemical properties of the element.