# 1.5 Practice Problems

1. Show $A$ and $Z$ information for all the major elements in Earth's crust in the correct format.
2. Determine the numbers of protons, neutrons, and electrons in each of the following species: $\ce{^{35}Cl}$, $\ce{^{37}Cl}$, $\ce{^{41}K}$, and $\ce{^{12}C}$.
3. An atom has $A=114$ and $66$ neutrons in its nucleus. What element is it?
4. What is the atomic and molar mass of $\ce{O}$ in Earth's atmosphere? The stable isotopic composition of $\ce{O}$ atoms is $\pu{99.759 \%}$ $\ce{^{16}O}$, $\pu{0.037  \%}$ $\ce{^{17}O}$ and $\pu{0.204  \%}$ $\ce{^{18}O}$.
5. How many moles of $\ce{As}$are there in $\pu{6.50 g}$  of $\ce{As}$?
6. How many atoms are there in $\pu{3.559e-6 mole}$ of $\ce{Kr}$?
7. How many atoms are there in $\pu{30.1 g}$ of $\ce{Mg}$?
8. What mass of $\ce{Hg}$ contains the same number of atoms as $\pu{90.15 g}$ of $\ce{Hg}$?
9. Calculate molecular and formula masses for the following compounds: (i) citric acid ($\ce{H3C6H5O7}$), (ii) barium acetate ($\ce{Ba(C2H3O2)2}$), and (iii) caffeine molecule shown in {numref}`caffeine`.
10. Determine the percent composition by mass of (i) sodium bicarbonate ($\ce{Na2CO3}$), (ii) lithium carbonate ($\ce{Li2CO3}$), and (iii) kaolinite ($\ce{Al2Si2O5(OH)4}$).
11. How many orbitals are in a subshell designated by the quantum numbers $n = 3, l = 2$?
12. How many subshells are in the shell designated by $n = 3$? 
13. What is the total number of orbitals in the shell designated by $n = 4$?
14. What is the minimum value of the principal quantum number for an orbital in which $m_l = +2$?
15. Write the electron configuration of the following elements: $\ce{Ti, Cr, Fe, Hg, Si, Se, Ar}$. 
16. Identify the element represented by the following electron configuration: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^4$
17. Write the abbreviated electron configuration of $\ce{Ti, Cr, Fe, Hg, Si, Se, Ar}$ using the correct *noble gas core*.
18. What element is represented by the following electron configuration: $[\ce{Kr}] 5s^2 4d^{10} 5p^5$?
19. Write Lewis dot symbols for (a) $\ce{F-}$, (b) $\ce{K+}$, and (c) $\ce{S^2-}$ (sulfide).  Hint: Write the Lewis dot symbol for each element first, then add or remove electrons to get the correct ionic form.
20. Is it possible to determine the group number of a main group atom by looking at the Lewis dot symbol of its common ion? Explain.
21. Show the Lewis structure of (i) $\ce{C2H4}$ (ethylene), (ii) $\ce{N2}$, and (iii) $\ce{C2H2}$ (acetylene). (Hint: There is a double bond in ethylene and a triple bond in other two molecular structures.)
22. Name the following ionic compounds: (a) $\ce{CaO}$, (b) $\ce{Mg3N2}$, and (c) $\ce{Fe2S3}$.
23. Deduce the formulas of the following ionic compounds: (a) mercury (II) chloride, (b) lead (II) bromide, and (c) potassium nitride.
24. Balance the following chemical reactions using an approach you find that works for you:

$$
\begin{align*}
\ce{
PbO2 &-> Pb^2+ + O2 \\
CaAl2Si2O8 + H+ &-> Ca^2+ + Al^3+ + H4SiO4 \\
FeOOH + H+ &-> Fe^3+ + H2O\\
KAlSi3O8 + H2O + H+ &-> K+ + Al^3+ + H4SiO4 (aq)\\
Mg5(CO3)4(OH)2 * 4 H2O + H+ &-> Mg^2+ + CO3^2- + H2O
}
\end{align*}
$$