# Atomic Structure Exam 2 and Problem Solutions

**Atomic Structure Exam 2 and Problem Solutions**

**1.** Which ones of the following relations about _{7}^{14}X^{-3} ion are true?

**I.** p^{+}=n^{0}

**II.** e^{-}>p^{+}

**III.** Mass Number =p^{+} + e^{-}

**Solution:**

Atomic number=number of protons =7

p^{+}=7

Mass number=p^{+} + n^{0}

14=7+n^{0}

n^{0}=7

n^{0}=p^{+}=7 I is true

We find charge of ion as;

charge of ion=p^{+} - e^{-}

-3=7-e^{-}

e^{-}=10 (e^{-}>p^{+}) II is true

Mass number is 14 on the contrary, sum of p^{+} and e^{-} is 17

III is false.

**2.** Positively charged ions are called cation and negatively charged ions are called anion. Table given below shows number of electrons and protons of given elements.

Which ones of the elements given above are cation?

**Solution:**

In a neutral atom number of protons is equal to number of electrons.

Number of protons of X is larger than number of electrons, so X is cation.

Number of protons of Y is equal to number of electrons, so Y is neutral.

Number of protons of Z is larger than number of electrons, so Z is cation.

**3.** If number of electrons of X^{+3}, Y^{-3} and Z are equal, which ones of the following statements are true for them.

**I.** X has largest nuclear charge

**II.** Volume of Y^{-3} ion is larger than others

**III.** Attraction of one electron;

X^{+3}> Z > Y^{-3}

**Solution:**

Let me show number of electrons with “a”. Charge of ion can e found with following equation;

charge=p+-e^{-}

For X^{+3} ion;

+3=p^{+}-a then, p+=a+3 and _{a+3}X^{+3}

For Y^{-3}ion;

-3 = p+-a then, p+=a-3 and _{a-3}Y^{-3}

For Z atom;

p^{+}=e^{-} then p^{+}=a and _{a}Z^{0}

charge of nucleus is equal to number of protons. So, X has largest nuclear charge. I is true.

Since they have equal number of electrons, attraction of one electron is directly proportional to number of protons. If number of protons increases then, attraction of electrons also increases. Thus, relation becomes;

X^{+3} > Z > Y^{-3} III is true

Volume is inversely proportional to attraction of one electron.

X^{+3} < Z < Y^{-3}II is true

**4.** Cu has two isotopes; ^{63}Cu in 70 % and ^{65}Cl in 30%. Find average atomic mass of Cu atom.

**Solution:**

We use following formula to fşnd average atomic mass of Cu;

Average atomic mass of Cu=63.(70/100) + 65.(30/100)

Average atomic mass of Cu=63,6 g

**5.** Find Atomic number of element that has electron configuration lasting with 6p^{2}.

**Solution:**

To find atomic number of element, we should write all orbitals until 6p^{2} and sum number of electrons.

1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}4f^{14}5d^{10}6p^{2}

Sum of number of electrons is 82. So it also has 82 protons and atomic number is 82.

**6.** Find number of filled and half filled orbitals of _{14}Si element.

**Solution:**

We first write electron configuration of _{14}Si and then show electrons in orbitals.

_{14}Si: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}

Orbitals;

As you can see from the given diagram, _{14}Si has 6 filled and 2 half filled orbitals.