Periodic table is the representation of elements in an order
The history of periodic table can be summarized as
a) 1829 : Johann Dobereiner proposed the triad rule. According to him we can classify the elements in a triad where the atomic mass of middle element is average of atomic mass of the near by two atoms.
For example : Li, Na and K is a triad. Where atomic mass of Na is average of atomic mass of K
atomic mass of Na = 7+ 39 / 2 = 23
However, with the further discovery of elements the law was rejected.
b) 1864 : John Newland proposed the law of octave. According to him we can arrange the elements in a set of seven elements where the property of second set of seven elements will resemble the properties of first of seven elements or property will be repeated after seven elements. This was also rejected due to its limited applicability.
c) Meyer : He arranged some 28 elements into six different families based on their atomic masses. The members of each familiy shared some common properties.
d) 1869 : Mendleev : He actually developed a periodic table based on atomic mass of elements. He arranged the elements into groups and periods. He even left space for some undiscovered elements, which were later on discovered.
e) 1916 : Henry Moseley : He finally arranged elements based on their atomic number based on X-ray studies. He proposed the modern periodic law that the periodic properties of elements are due to atomic number of elements.
So, we have:
- molecular weight
- shape
- temperature
- kinetic energy
- mass
- density
Let's rule out the different options.
- molecular weight: Say you have a molecule of H2O. H2O can be a solid, liquid, or gas, but its molecular weight never changes throughout (It's still the same molecule, no matter what phase it is in). We can rule this out.
- shape: Let's pretend we have three identical closed containers, and we fill each one halfway with water, blocks of ice cubes, and water vapor. In the container with water, you will see that the water takes the shape of the container, but doesn't fill the entire container up. The ice cubes will stay ice cubes, assuming they don't melt, so they don't take the shape of the container. The vapor will fill up the entire container. Since all three are different, I would say yes, this could be a distinguishable feature.
- temperature: In general, I would say no, because every element/molecule has different boiling points and different vaporization points. So if you have a liquid at 5°C, you could also have a different element in solid form at 5°C. But if you're comparing a single type of molecule, it would have a boiling point and a vaporization point, so you <em>would</em> be able to tell between them.
- kinetic energy: Kinetic energy refers to how much movement there is in respect to each molecule. In solids, the molecules are packed tightly together and can't move very much, so they have lower kinetic energy. In liquids, they are less packed, but still restricted. And in gases, they can fly freely, so they will have much more kinetic energy than liquids or solids. This one's a yes.
- mass: No matter what form, there are still the same amount of molecules, and each molecule has the same mass as before. It won't change.
- density: Since the molecules are more spread out in gases, it will be less dense. Liquids will be more dense, and solids will have the greatest density. So, yes.
Conclusion: shape, kinetic energy, density, (and temperature if it's talking about a single type of molecule)
The answer is (3) 3. The calculation rule of significant figures is when multiplication and division, the significant figures of result is equal to the least of the numbers involved. The significant figure of 2.70 and 80.01 is 3 and 4.
