chemistry study guide 2?

Question

9 two man-made elements with atomic number greater than 92 are
americium and curium
thorium and actinium
U238 and U239
U235 and U238


10 the particle which has the same number of orbital electrons as a potassium ion is
Ce+3
K0
Ne0
S-2


11 the atomic number of an element that is chemically like magnsium is
5
9
14
20


12 atoms of u-235 and U-238 differ in structure by 3...
electrons
mesons
neutrons
protons


13 tritium an isotope of hydrogen, has an atomic number of



14 the max number of electrons possible in the second ring of an atom is
6
2
8
4


15 when an atom loses 2 electrons it becomes an ion with a charge of
-2
+2
-6
+6


16 when each of the following elements forms ions the one that does not have 8 electrons in its outer ring is
calcium
chlorine
hydrogen
sodium


17 the atomic number of an inert element is....

11
18
51
78

Answer 1

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.

9: Americium and Curium (wikipedia!)

10: 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...

11: 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

12: 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.

13: Same explanation as above, it'll also be Hydrogen's atomic number because it's an isotope.

14: 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...

15: If an atom loses electrons, it's LOSING -1 per electron lost, so it's becoming more positive.

16: 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)?

17: 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...

Answer 2

1. Convert grams of N to moles of N using the atomic mass. Convert moles of N to molecules of N using avagadros number. Be sure to use dimensional analysis so that your units cancel. This will mean dividing grams of N by the atomic mass of N and then multiplying by avagadros number. 2. Do the opposite of above. Convert molecules of Ni to moles of Ni using avagadros number and then convert moles to grams using the atomic weight of Ni. 3. Half-life means that 1/2 the sample decays. So the question is how does this translate into 75%. Let's think about it. in one half life, half is gone. Now we only have 50%. After a second half-life, half of that is gone. That leaves 1/2 of half. That means that 75% is gone. So it will take two half-lives. 4. There is an equation for half life. Amount of sample remaining = original amount of sample * (0.5)^(number of half lives) So to answer this question you need to figure out first how many half lives 27 hours is and plug that in. (This will be the Time/half life, making sure the units are the same). Then you can enter 1 for the starting amount of sample and solve for the remaining amount. Then if you divide the remaining amount of sample by 1 and multiply by 100% you will have the percent remaining. 5. To write molecular formulas, you first figure out the charge on each molecule. In this case you need the charge on V and P (phosphide). The question tells you the charge on Vanadium by the number in the parentheses so it is V+2. Phosphide you need to figure out from the periodic table. Find phosphorus. Start on the right of the table and count how many blocks from last row it is. (should be 4) Since we counted from the right, we know it is negative so the charge on P is -4. Then we take the charge on V and make it the subscript on P and vice a versa. This means we have V4P2, where 4 and 2 are subscripts. Hope this helps.