As you go across a certain period what happens to the size of the atoms: e.g. from Na->Mg->Al ?
812707
The size of the atom increases across the table as more electrons are added to the shell.  Look at it logically.  The size of an atom with 8 electrons in the outer shell compared to an atom with one electron in the outer shell despite the increase in the charge of the nucleus.  Negative charges, (the electrons), repel.
538049
Yes.  In fact protons even from two different elements are indistinguishable.  This is a fundamental property that is quite interesting, and it results in some very odd behavior.
1071585
assume 0.1mm3\n6.02e22 mm3\n6.02e19 cm3 \n6.02e13 m3\n6.02e5 km3\nroughly 602,000 km3
921116
I'm not directly giving you the answers, you have to know how to do this stuff, but I'll give you the process to get to each.\n\n9: Americium and Curium (wikipedia!)\n\n10: Potassium ion wants to be like the noble gas closest to it (the one right before it), so it loses 1e- to get there and be K+.  If that's not a choice, then look for another ion, positive or negative, that adds up to the electronic configuration of the aforementioned noble gas. (1s2 2s2 2p6 3s2 3p6), 18 total e-'s...\n\n11: Mg is in column 2, things in the same period tend to be chemically similar.  Find the other one in the choices that's in that column\n\n12: U235 and U238 are isotopes, same atomic number, different weight.  If you change the number of protons, you change the atomic number, so that wouldn't be U anymore.  Changing electrons can make ions, but not change weight.  So different number of neutrons for the same element makes an isotope.\n\n13: Same explanation as above, it'll also be Hydrogen's atomic number because it's an isotope.\n\n14: shell 2 contains the 2s and 2p subshells.  2s can hold 2 because it's an s orbital.  2p can hold 2 per p orbital, and a p subshell has 3 p orbitals, so 6.  Total would then be...\n\n15: If an atom loses electrons, it's LOSING -1 per electron lost, so it's becoming more positive.\n\n16: Which element in that list only has 1s shell? Which one has a  stable ion as just a proton or with a configuration like Helium (1s2)?\n\n17: Inert elements are on the far right of the periodic table.  They are inert because they have 8 valence (outer shell) electrons (or 2 in Helium's case) so they can't take anymore and are stable.  Look at your periodic table or count up electrons for each of those atomic numbers.  Only one of them will have 8 in the outer shell...
462594
As you go down, the electrons occupy energy levels whose energy is greater. That is, they are farther away from the nucleus. For example an element in period 6 has its outtermost electrons in the n=6 energy level. These electrons have a greater potential energy than those in the n=2 level because they are farther away from the nucleus. This is similar to an object that is higher up: It has a greater gravitational potential energy. The size of the atom increases because as more electrons are present in an atom, the more energy levels they fill. The outtermost occupied energy level of an atom is what determines size.
883178
A) Valence Electrons\n\nI believe b, c and d show the results of the grouping not the reason they're grouped that way to start out with...\n \nb... No... The atom size increases instead of decreases\nc... No...\nc... No...  \nversa...
905373
if u are referring to expansion due to heating than the order of expansion of the substances from lowest to largest is solid, liquids, than gases. But a solid's expansion is extremely low, almost impossible to measure unless its a metal.
425506
Depending on the value of the fine-structure constant, it will change your answer.\n\nThe fine-structure constant has been cited as:\n\n7.297 352 568 x 10^-3\n\n1/137.035 999 11\n\n1/137\n\n1/136
608949
cant answer secifically, but you should be able to back calculte taking elements present today and using the half lives as your main variable.
727822
It is 63 x 0.66 + 65 x 0.34.  Do you see why?  The actual atomic weight found in the periodic table will differ from this by a tad because of nuclear binding energy.
107512
I’m not entirely clear in what question you are asking, but the answer is ‘No’, whatever you mean.\n\nAre you asking if, for example, a Uranium atom and a hydrogen atom occupy the same volume at the same temperature? If that is the question then the answer is an unambiguous “No”. Different atoms have different atomic radii. The atomic radius is a reresentation of how much space the electrons of the atom occupy at standard temperature (25oC). Since Uranium has an atomic radius orders of magnitude higher than Hydrogen it obviously occupies far more volume at the same temperature.\n\nExtending that, since U occupies more volume the H any compound made with U in place of H must also occupy more volume. Eg HO will occupy far less volume than UO\n\n\nOr are you asking if all atoms or molecules of the same type occupy the same volume at the same temperature? For example do all water molecules on a glass at 25oC  occupy the same space? In which case this is a trick question designed to make you think about the difference between temperature and heat. And the answer is still “No”.\n\nOr are you asking if two substances made of different molecules occupy the same volume? For example does a mg of water occupy the same space as a mg of ethanol.
873114
→ Atomic radius decreases → Ionization energy increases → Electronegativity increases →\n\nIn general, the degree of electronegativity decreases down each group and increases across the periods, as shown below. Across a period, non-metals tend to gain electrons and metals tend to lose them due to the atom striving to achieve a stable octet. Down a group, the nuclear charge has less effect on the outermost shells. Therefore, the most electronegative atoms can be found in the upper, right hand side of the periodic table, and the least electronegative elements can be found at the bottom left. \n\nGenerally speaking, atomic ionization energies decrease down a group of the periodic table, and increase left-to-right across a period. Ionization energy exhibits a strong negative correlation with atomic radius.
876338
All three of these ions have the same number of electrons, they are "isoelectronic."  The size of the ions thus depends on the number of protons in the nucleus.  As we move to the right across a row on the periodic table, the number of protons in the nucleus, and thus the nuclear charge, increases.  This increase in nuclear charge pulls the electrons in tighter, thus reducing the size of the ions.  Na+ > Mg2+ > Al3+
905246
Yes.  You just begin to take electrons away from the outermost, least stable orbitals.  In this case the first two electrons will come from the 4s2 shell, and then the one from the 3d.  This will leave you with just [Ar], which is a noble gas, and if you remember back to the beginning of chemistry, elements become ionic (gain or lose electrons) because they all wish to achieve this noble gas configuration.
462911
relative atomic mass of magnesium (Mg) is 24.5
210441
The amount of protons it has decides what element it will be. For compound things, it matters on what elements it is made up of and the structure of the lattice that bonds the atoms together.
875588
For C, that would normally be true.\n\nFor D, the answer is 1.2X10^24 atoms.\n\nFor E, helium atoms escaped through effusion.