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What else can I help you with?
How can you calculate the mass of an atom?
As you have probably learned, an atom is a very, very small object. However, we can easily handle a very large group of atoms and weigh that. If we have an idea of how to figure out how many atoms are in that particular group, we can simply divide the mass of the group into the individual atoms in that group. For example, let us say for the moment that we know that there are 1000 atoms of carbon for every 1g of charcoal, if I get the mass of a piece of charcoal (which is pure carbon) and it turns out to be 2g in mass, then I know that there are 2000 atoms of carbon in there. The tricky part is knowing how many atoms of carbon are in 1g of charcoal. Here is the problem, as you already noted, we can say that 1 oxygen atom is equivalent in mass to 16 hydrogen atoms, this would be good if we knew what the mass was of either oxygen or hydrogen. Let us say, we did not, but we knew that 12 atoms of hydrogen were equivalent to the mass of 1 carbon atom, then if we knew the mass of carbon, then we could know the mass of hydrogen and oxygen. But let us say we did not know the actual mass of any atom, what then? All we have are relative masses, the mass of an atom in relation to another atom. What we need is a starting point. Scientists simply agreed that 12g of carbon atoms would contain a "mole" of carbon atoms. At this point, it does not matter how many atoms are in a mole, let us say for the moment that it turns out that there are 12 atoms in a mole (a mole in this case is just like "dozen") then each atom of carbon must have a mass of 1g (12g divided by 12atoms). Then we can say that the mass of a hydrogen is 1/12g (since 1 carbon is to 12 hydrogen) and the mass of oxygen is 16/12g (or 4/3g, since 16 hydrogens is 1 oxygen). The point here is that once we agree on a grouping of atoms (the mole) and agree on the mass of that grouping for one of the atoms, then we would know the mass of all the other atoms. Once we have our starting point, we know all the relative masses.
Why might blue light cause emission of electrons from metal while red light does not?
Blue light will eject electrons from a photosensitive surface because blue light has a high frequency. The high photon frequency of the blue light means it has more energy because the frequency is directly linked to the energy of the photons. Red light would not eject electrons because it has a low frequency.
