## Quiz atomic structure

$\require{mhchem}$

#### Worked exercises

1. Calculate the number of protons, electrons and neutrons present in the atom $$\ce{_{18}^{40}Ar}$$.

Atomic number (Z) $$=18$$
Mass number (A) $$=40$$

Atomic number $$=$$ Number of protons $$=$$ Number of electrons Therefore, number of protons $$=18$$ and number of electrons $$=18$$ Mass number $$=$$ Number of protons $$+$$ Number of neutrons

Number of neutrons $$=$$ Mass number $$-$$ Number of protons
Number of neutrons $$=40-18$$
Number of neutrons $$=22$$

2. The atomic number of the Lithium atom is $$3$$, and its mass number is $$7$$. Calculate the total number of nucleons present in the atom.

Protons and neutrons are nucleons.
Total number of nucleons $$=$$ Number of protons $$+$$ Number of neutrons
Mass number $$=$$ Number of protons $$+$$ Number of neutrons
Therefore, the total number of nucleons $$=$$ Mass number, which is $$7$$

3. Determine the number of neutrons present in Iodine isotopes.
a. $$\ce{_{53}^{125}I}$$
b. $$\ce{_{53}^{131}I}$$

Number of neutrons $$=$$ Mass number $$-$$ Atomic number

a. Number of neutrons $$=125-53=72$$

b. Number of neutrons $$=131-53=78$$

4. Chlorine naturally exists in two isotopic forms: $$\ce{_{17}^{35}Cl}$$, $$\ce{_{17}^{37}Cl}$$. Each isotope’s relative percentage abundance and atomic mass are given in the following table. Calculate the atomic mass of Chlorine.

Isotopes Relative percentage abundance Atomic mass (amu)
Chlorine-$$35$$ $$75.53$$ $$34.97$$
Chlorine-$$37$$ $$24.47$$ $$36.97$$
Chlorine’s atomic mass is calculated by multiplying the atomic mass of each isotope by its percentage abundance and then totalling the answers obtain for each isotope.
Chlorine-$$35$$ $$=\frac{75.53}{100}\times34.97\,amu=26.41\,amu$$
Chlorine-$$37$$ $$=\frac{24.47}{100}\times36.97\,amu=9.047\,amu$$
Atomic mass of Chlorine $$=26.41\,amu+9.047\,amu=35.46\,amu$$

#### Exercises

1. Which of the following statement about subatomic particles is incorrect?

a. Proton, neutrons and electrons are subatomic particles.

b. Electrons have no charge

c. Protons are positively charged

d. Protons and neutrons are almost equal in their weights

b Electrons have no charge

2. Which of the following statement about the nucleus is correct?

a. Nucleus of an atom contains protons and neutrons

b. Nucleus of an atom is negatively charged

c. Nucleons are present in both nucleus and orbitals

d. Nucleus of an atom is much larger than its surrounding electron cloud.

a Nucleus of an atom contains protons and neutrons

3. What is the atomic number of $$\ce{_{17}^{37}Cl}$$?

a. $$17$$

b. $$37$$

c. $$20$$

d. $$54$$

a $$17$$

4. What is the mass number of $$\ce{_{16}^{32}S}$$?

a. $$16$$

b. $$48$$

c. $$32$$

d. $$34$$

c $$32$$

5. Determine the number of protons present in an atom with an atomic number of $$9$$ and a mass number of $$19$$.

a. $$19$$

b. $$9$$

c. $$10$$

d. $$28$$

b $$9$$

6. Determine the number of neutrons present in the nucleus of $$\ce{_{11}^{23}Na}$$.

a. $$11$$

b. $$23$$

c. $$12$$

d. $$34$$

c $$12$$

7. What is the number of electrons present in element $$\ce{Mg}$$($$A=24,\,Z=12$$)?

a. $$24$$

b. $$12$$

c. $$10$$

d. $$13$$

b $$12$$

8. What is the total number of nucleons present in $$\ce{_{4}^{9}Be}$$?

a. $$4$$

b. $$8$$

c. $$9$$

d. $$5$$

c$$9$$

9. Determine the total number of subatomic particles present in an atom with $$Z=48$$ and $$A=110$$.

a. $$48$$

b. $$110$$

c. $$158$$

d. $$62$$

c $$158$$

10. Determine the atomic number and mass number for an atom with $$12$$ protons, $$10$$ neutrons and $$12$$ electrons.

a. $$Z=12$$ and $$A=22$$

b. $$Z=22$$ and $$A=12$$

c. $$Z=12$$ and $$A=24$$

d. $$Z=10$$ and $$A=22$$

a $$Z=12$$ and $$A=22$$

11. Which of the following pairs has the same number of neutrons?

a. $$\ce{_{7}^{13}C}$$ and $$\ce{_{6}^{13}N}$$

b. $$\ce{_{17}^{37}Cl}$$ and $$\ce{_{18}^{36}Ar}$$

c. $$\ce{_{17}^{35}Cl}$$ and $$\ce{_{17}^{37}Cl}$$

d. $$\ce{_{8}^{18}O}$$ and $$\ce{_{9}^{19}F}$$

d $$\ce{_{8}^{18}O}$$ and $$\ce{_{9}^{19}F}$$

12. Which of the following statement about isotopes of an element is incorrect?

a. The number of protons and electrons present in isotopes of an element is constant

b. All isotopes of an element have the same atomic number

c. Not all isotopes of an element contain the same number of neutrons

d. All isotopes of an element have the same mass number

d All isotopes of an element have the same mass number

13. Which of the following pair are isotopes?

a. $$\ce{_{14}^{28}Si}$$ and $$\ce{_{14}^{29}Si}$$

b. $$\ce{_{18}^{40}Ar}$$ and $$\ce{_{20}^{40}Ca}$$

c. $$\ce{_{6}^{14}C}$$ and $$\ce{_{7}^{15}N}$$

d. $$\ce{_{18}^{38}Ar}$$ and $$\ce{_{19}^{39}K}$$

a $$\ce{_{14}^{28}Si}$$ and $$\ce{_{14}^{29}Si}$$

14. Determine the number of neutrons present in each of the Uranium isotopes: Uranium-$$235$$($$\ce{_{92}^{235}U}$$) and Uranium-$$239$$ ($$\ce{_{92}^{239}U}$$).

a. Uranium-$$235$$: $$143$$ and Uranium-$$239$$: $$147$$

b. Uranium-$$235$$: $$92$$ and Uranium-$$239$$: $$147$$

c. Uranium-$$235$$: $$147$$ and Uranium-$$239$$: $$92$$

d. Uranium-$$235$$: $$92$$ and Uranium-$$239$$: $$143$$

a Uranium-$$235$$: $$143$$ and Uranium-$$239$$: $$147$$

15. Determine which pairs of atoms are isotopes using the provided information in the following table.

p n e
Atom A $$8$$ $$10$$ $$8$$
Atom B $$6$$ $$6$$ $$6$$
Atom C $$8$$ $$8$$ $$8$$
Atom D $$6$$ $$7$$ $$6$$

a. Atom A and B

b. Atom C and D

c. Atom A and C, Atom B and D

d. Atom B and C, Atom A and D

c Atom A and C, Atom B and D

16. Calculate the atomic mass of Lithium using the following information.

% abundance Atomic mass (amu)
$$\ce{_{3}^{6}Li}$$ $$7.42$$ $$6.01$$
$$\ce{_{3}^{7}Li}$$ $$92.58$$ $$7.02$$

a. $$7.95\,amu$$

b. $$6.95\,amu$$

c. $$7.02\,amu$$

d. $$6.51\,amu$$

b $$6.95\,amu$$

17. Determine the atomic mass of $$\ce{Mg}$$ using the information given in the following table.

% abundance Atomic mass (amu)
$$\ce{_{12}^{24}Mg}$$ $$78.99$$ $$23.99$$
$$\ce{_{12}^{25}Mg}$$ $$10.00$$ $$24.99$$
$$\ce{_{12}^{26}Mg}$$ $$11.01$$ $$25.98$$

a. $$24.31\,amu$$

b. $$25.67\,amu$$

c. $$24.98\,amu$$

d. $$30.87\,amu$$

a $$24.31\,amu$$

18. Which of the following statement about silver isotopes is true?

a. $$\ce{_{47}^{109}Ag}$$ has two more electrons than $$\ce{_{47}^{107}Ag}$$

b. $$\ce{_{47}^{109}Ag}$$ and $$\ce{_{47}^{107}Ag}$$ contain the same number of neutrons

c. $$\ce{_{47}^{109}Ag}$$ and $$\ce{_{47}^{107}Ag}$$ have the same atomic number

d. $$\ce{_{47}^{109}Ag}$$ has two more protons than $$\ce{_{47}^{107}Ag}$$

c $$\ce{_{47}^{109}Ag}$$ and $$\ce{_{47}^{107}Ag}$$ have the same atomic number