How are mass number and atomic mass related?
107880
The atomic mass is equal (approximately) to the number of protons plus the number of neutrons.  The atomic number indicates the number of protons.  So atomic mass is atomic number plus the number of neutrons in the atom.
244528
There are some numbers such as 20, 82, etc. which signifyu that if the difference between the number of protons and neutrons or the umber of protons or the number of neutrons are equal to that number then the nucleus is especially stable. No exact scientific reason is present to explain this effect. So these are called magic numbers.
902490
Silicon's elemental number is 14, meaning it has 14 protons. If the atomic weight is 28, then subtracting 14 (the mass of the protons) gives you the solution, 14 neutrons.\n\nAtomic mass = mass of protons + mass of neutrons + a tiny bit of mass from electrons.\n\nProtons and neutrons have nearly the same mass, and electrons have hardly any mass at all.
450990
The mass of a nucleus indicates the number of protons and neutrons present in the nucleus. An element can have more than one isotope eg Carbon 12 and Carbon 14. The former has 6 protons and 6 neutrons, The latter 6 protons and 8 neutrons. \n\nThe atomic weight of an isotope refers to the numbers of protons AND neutrons present. The atomic number of an element refers to the number of protons in all its isotopes.\n\nHydrogen, though normally just a solo proton in its nucleus, does have two isotopes, deuterium, with 1 neutron, and tritium with two neutrons.\n\nA recent question asked about silver, how many of each in its nucleus. Its atomic number is 47, so clearly 47 protons. Naturally-occurring silver is given as having  an atomic weight of 108, so answerers answered 61 neutrons.\n\nHowever there is a subtlety they missed..\n\nNaturally-occurring silver is a mixture of Ag 107 (60 neutrons) and Ag 109 (62 neutrons). (Slightly more than 50% of the former.).\n\nSo the average atomic weight of the two isotopes is 108. But there is no Ag 108 isotope present. The wrong inference was drawn.\n\nSeveral people above are confusing atomic weight and atomic number, and what they each mean. So if you don't understand several of the answers it is because they are jumbled versions of the true picture.
960826
I will assume you mean "mass divided by molecular mass." The molecular mass is, by definition, the mass of one mole of a substance. Thus, if you take a given mass and divide it by the molar mass, you will get the number of moles.  A good way to do this is to use demensional analysis, where you start with you mass (x grams) use your molar mass as the conversion (Z moles/ygrams) and multiply the two so that the grams cancel, leaving you with moles.
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!
172739
The atomic number is representative of the number of protons in the nucleus.  The atomic mass is representative of the number of total particles in the nucleus, which is made up solely of protons and neutrons.  That means that (35 total particles)-(17 protons)=18 neutrons.
43865
The molecular mass (abbreviated MM) of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). Due to this relativity, the molecular mass of a substance is commonly referred to as the relative molecular mass, and abbreviated to Mr.\n\nThe molecular mass can be calculated as the sum of the atomic masses of all the atoms of any one molecule. The molecular mass can also be measured directly using mass spectrometry. In mass spectrometry, the molecular mass of a small molecule (< ~200 atoms of a given element) is exact, that is, the sum of the most common isotopes of each element. Of larger molecules, it is average, or calculated using the elemental mass number or the periodic table, since there is likely to be a statistical distribution of atoms representing the isotopes throughout the molecule.\n\nThe molar mass of a substance is numerically equal to the molecular mass, but expressed in mass units per mole, usually as g/mol (grams per mole).\n\nExample: \nThe atomic mass of hydrogen is 1.00784 u and that of oxygen is 15.9994 u; therefore, the molecular mass of water with formula H2O is (2 × 1.00784 u) + 15.9994 u = 18.01508 u. Therefore, one mole of water weighs 18.01508 grams. However, the exact mass of hydrogen-1 (the most common isotope) is 1.00783, and the exact mass of oxygen-16 (the most common isotope) is 15.9949, so the mass of the most common single molecule of water is 18.0105 u. \nMolecular mass or molar mass are used in stoichiometry calculations.\n\nSince molecules are created by chemical reactions, not nuclear reactions, a molecule's molecular mass exactly equals the sum of the atomic masses of its constituent atoms.\n\nThe gram-molecular weight is the molecular weight of a chemical compound expressed in grams. Thus the molecular weight of calcium carbonate is 100 therefore the gram-molecular weight is 100 g. The Gram Molecular Weight is frequently used, particularly for calculating the concentration of solutions. Thus a molar solution will contain the gram molecular weight of a chemical dissolved to produce one litre of solution.\n\nHandy Little Calculator:\nhttp://www.chemie.fu-berlin.de/cgi-bin/molform
365377
atomic number represents the number of protons or electrons in an atom
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
693553
The atomic number of an element is equal to the number of protons the element has in the nucleus of one atom.\nThe number of protons in the nucleus determine what element it is.\n\nThe atomic mass of an element is equal to the sum of number of protons and the number of neutrons in the nucleus.  The electrons around the atom are neglected since their mass is negligible, as well as the fact that atoms can form ions by gaining and/or loosing electrons even though the element is the same.
609337
The atomic mass of a chemical element is the mass of an atom at rest, most often expressed in unified atomic mass units. The atomic mass is often synonymous with relative atomic mass, average atomic mass and atomic weight; however, it is subtly different in that it can either be the abundance-weighted average of isotope masses of an element or the mass of a single isotope.\n\nThe relative atomic mass (also known as atomic weight and average atomic mass) is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance. Periodic tables usually list these with reference to the local environment of Earth's crust and atmosphere. An uncertainty in parenthesis is often included. For artificial elements the nucleon count of the most stable isotope is listed in brackets as the atomic mass
16762
The atomic number is the number of protons.
1075835
20.\n\n40 - 20 = 20.\n\nThe mass number is the number of protons and neutrons combined. The atomic number is the number of protons.
482427
The "atomic" number refers to the place in the periodic table which corresponds directly (is equal to) the number of protons. The mass number is a weighted average involving commonly found isotopes.
944969
Molar Mass Conversion Factors Help \nFor example, the atomic mass of magnesium (24.3050) shows us that the average mass of magnesium ... For example, the atomic mass of the element neon listed ...www.mpcfaculty.net/mark_bishop/molar_mass_conversion_factors_help.htm
497438
The atomic number is equal to the number of protons.\nThe mass number is equal to protons plus neutrons.\n\nThe difference between those two numbers would equal the number of neutrons.