Physics 78 Online
OpenStudy (anonymous):

If an object has a volume of 2 milliliters and a mass of 10 grams, calculate the density of the object. If a neutral atom has a mass of 15 amu and an atomic number of 7, determine the number of protons, neutrons, and electrons in the atom.

OpenStudy (anonymous):

It is a bother in the beginning, but it is convenient to show that any volume comes in such an such Cubic unit. \[Mass/ Volume= Density\] In your case, you'll have "grams over cubic milliliters" The 7 accounts for the protons (which will NEVER change in amount inside the atom and still be the same element), then the next mass to find are the neutrons, which are Neutrals but have almost the same mass as the protons (Neutrons amount can change inside the atom and still be the same element, Isotope) then 15-7=8 So we have 8 Neutrons. Electrons have such an insignificant mass compared to that of the protons and neutrons that they are not accounted in the AMU.

OpenStudy (anonymous):

if i`m not mistaken, the atomic number also indicates the number of electrons. if there are 7 protons, then there is an equal amount of electrons, i.e. 7.

OpenStudy (anonymous):

if i`m not mistaken, the atomic number also indicates the number of electrons. if there are 7 protons, then there is an equal amount of electrons, i.e. 7.

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