Question

1. what is the formula for vanadium (iv) sulfate?

a. $v_4so_4$ d. $v_2(so_4)_2$
b. $v_4so_4$ e. $v_2so_4$
c. $v(so_4)_2$

1. isotopes of an element contain different numbers of...

a. electrons. c. neutrons.
b. protons. d. nuclides.

1. how many valence electrons does phosphorous have?

a. 7 c. 6
b. 15 d. 5

1. which of the following are isotopes?

a. $_{6}^{12}q$ and $_{6}^{13}q$
b. $_{6}^{12}q$ and $_{5}^{12}q$
c. $_{6}^{13}q$ and $_{5}^{12}q$
d. all of the pairs are isotopes.
e. you can’t tell without the symbols for the elements.

1. determine the density of a substance (g/ml) with a mass of 34.6 g and a volume of 0.045 l.

a. 769 g/ml c. 1.30 g/ml
b. 0.00130 g/ml d. 0.769 g/ml

1. which of the following dot structure is incorrectly drawn for an atom?

a. $\stackrel{\bullet}{mg}\bullet$ c. $\stackrel{\bullet\bullet}{\stackrel{\bullet}{\stackrel{\bullet}{ne}}}\stackrel{\bullet\bullet}{}$
b. $\stackrel{\bullet}{\stackrel{\bullet}{n}}\stackrel{\bullet}{\stackrel{\bullet}{}}$ d. $\stackrel{\bullet}{\stackrel{\bullet\bullet}{\stackrel{\bullet}{o}}}\stackrel{\bullet\bullet}{}$

1. what is the electron configuration for sulfur (atomic number 16)?

a. $ne 3s^2 3p^2$ c. $1s^2 2s^2 2p^5 3s^2 3p^5$
b. $1s^2 2s^2 2p^6 3s^2 3p^4$ d. $ne 3s^1 3p^5$

1. the nucleus of most atoms is composed of...

a. tightly packed protons.
b. tightly packed neutrons.
c. tightly packed protons and neutrons.
d. loosely connected protons and electrons.

1. the colors of light that are seen during the flame test experiment/demo were caused by...

a. the atom’s nucleus absorbing energy from the flame.
b. the electrons absorbing energy from the flame.
c. the atom’s nucleus releasing energy.
d. the electrons releasing energy.

Explanation:

1. Question7: Vanadium(IV) has a +4 charge, sulfate has a -2 charge. Balance charges: one $V^{4+}$ pairs with two $SO_4^{2-}$.
2. Question8: Isotopes share the same proton count, differ in neutron count.
3. Question9: Phosphorus is in group 15, has 5 valence electrons.
4. Question10: Isotopes have identical atomic number (subscript). $\ce{^{12}_{6}Q}$ and $\ce{^{13}_{6}Q}$ match this rule.
5. Question11: Convert volume to mL: $0.045 \text{ L} = 45 \text{ mL}$. Density is $\frac{34.6}{45} \approx 0.769$ g/mL.
6. Question12: Mg has 2 valence electrons, its dot structure should have two dots, not one.
7. Question13: Sulfur (Z=16) fills orbitals sequentially: $1s^2 2s^2 2p^6 3s^2 3p^4$.
8. Question14: Atomic nuclei are made of tightly bound protons and neutrons.
9. Question15: Flame test colors come from excited electrons releasing energy as visible light when returning to ground state.

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Answer:

1. 7. c. $\boldsymbol{\ce{V(SO_4)_2}}$
2. 8. c. neutrons.
3. 9. d. 5
4. 10. a. $\boldsymbol{\ce{^{12}_{6}Q}}$ and $\boldsymbol{\ce{^{13}_{6}Q}}$
5. 11. d. 0.769 g/mL
6. 12. a. $\boldsymbol{\ce{Mg \bullet}}$
7. 13. b. $\boldsymbol{1s^2 2s^2 2p^6 3s^2 3p^4}$
8. 14. c. tightly packed protons and neutrons.
9. 15. d. the electrons releasing energy.