Exercises on atomic structure (with commented template)

Test your knowledge with the 10 questions then on atomic structure. Check the comments after the feedback to clear your doubts about the topic.

question 1

The atom is the fundamental unit of matter and the subatomic particles that compose it are differentiated, for example, by mass, electrical charge and location.

Complete the table below with the missing information.

Particle	Symbol	Pasta (in unit of atomic mass)	Charge (in unit of electric charge - c.u.e.)	Location
Proton		core
Neutron	no		0
Electron	and	-1	electrosphere

see answer

Right answer:

Particle	Symbol	Pasta (in unit of atomic mass)	Charge (in unit of electric charge - c.u.e.)	Location
Proton	P		+1	core
Neutron	no		0	core
Electron	and		-1	electrosphere

The three fundamental particles that make up atoms are: protons (positively charged), neutrons (neutral particles) and electrons (negatively charged).

The nucleus is the central part of the atom, where the protons and neutrons are. Around this region are electrons.

O proton (p) is a particle that has a positive charge (+1), atomic mass 1 u and is located in the atomic nucleus.

O electron (e) is a particle that has a positive charge (-1), practically zero atomic mass, and is located in the electrosphere.

O neutron (n) is a particle that has zero electric charge, atomic mass 1 u and is located in the atomic nucleus.

question 2

The most abundant chemical element on planet Earth is oxygen. In addition to being present in the air and being vital for the breathing of living beings, it composes an indispensable substance for our survival: water (H₂O).

Look at the following table with the main information of the oxygen atom and analyze the following statements.

Symbol	O
atomic number	8
mass number	16
Eletronic distribution	1s^2 2s^2 2p^4

I. The oxygen atom has 8 protons.
II. The oxygen atom has 7 neutrons.
III. The oxygen atom has 7 electrons.
IV. In the valence shell of oxygen there are 6 electrons.

The statements are correct:

a) I and II
b) II and IV
c) I and IV
d) II and III

see answer

Correct alternative: c) I and IV.

a) CORRECT. The atomic number of a chemical element corresponds to the number of protons in its nucleus. Therefore, the oxygen atom, because it has Z = 8, has 8 protons.

b) WRONG. The mass number is the sum of the number of protons and neutrons, that is, A = Z + n. As the oxygen atom has 8 protons, so its nucleus also has 8 neutrons.

A = Z + n
16 = 8 + n
16 - 8 = n
n = 8

c) WRONG. The ground state atom is electrically neutral. This means that the number of protons is equal to the number of electrons. As the atomic number of oxygen is 8, this means that its electrons also have 8 electrons.

d) CORRECT. The valence shell is the outermost shell of the atom's electrons. As oxygen has only two layers, so the outermost layer is layer 2, which contains 6 electrons: 2 electrons in the s sublevel and 4 electrons in the p sublevel.

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question 3

Electrons are subatomic particles that orbit around the atomic nucleus at well-defined energy levels.

Sodium (Na) is a chemical element with atomic number 11 and its electron distribution is 1s²2s²2p⁶3s¹.

Regarding the arrangement of electrons in the electrosphere of the sodium atom, it is correct to state that

a) The only shell filled with the maximum number of electrons is the first shell.
b) The electrons of the sodium atom are distributed in three energy levels.
c) The electron that is used to make a chemical bond with another atom must be located in the second electron shell of the sodium atom, as it has the most electrons available.
d) The stability of the sodium atom is acquired by receiving electrons to completely fill the last electron shell.

see answer

Correct alternative: b) The electrons of the sodium atom are distributed in three energy levels.

a) WRONG. The first and second layers in the electronic distribution have the maximum number of electrons possible.

electronic layer	maximum number of electrons	Distribution of electrons
K	2	1s^2
L	8	2s^2 2p^6

b) CORRECT. Altogether, an atom can contain up to 7 energy levels, named K through Q. Because it has 11 electrons, the sodium atom fills three electron shells: K, L and M.

Energy level	electronic layer	Distribution of electrons
1º	K	1s^2
2º	L	2s^2 2p^6
3º	M	3s^1

c) WRONG. The electrons used for a chemical bond are located in the outermost shell of the atom. Therefore, the electron that is located in the s sublevel of the M shell is what will be used to make an association with another atom.

d) WRONG. Sodium is a low electronegativity element and, therefore, has a tendency to donate electrons instead of receiving them. Therefore, to become stable, the sodium atom establishes a chemical bond of the ionic type, because when transferring its electron to a more electronegative atom, the ion Na is created.⁺, whose electronic distribution is 1s² 2s² 2p⁶.

know more about eletronic distribution.

question 4

The nitrogen atom has atomic number 7. In the ground state, as the atom is electrically neutral, the electrosphere of this chemical element has 7 electrons.

Knowing that the electron distribution of nitrogen is 1s²2s²2p³, correctly fill in the location of electrons in the following orbitals.

see answer

Right answer:

Atomic orbitals correspond to the regions where electrons are most likely to be found. Each orbital holds a maximum of 2 electrons and this filling is done from the electronic distribution.

In the electronic distribution of orbitals, we initially fill all the orbitals with an electron in the same direction, which is facing upwards. After all the orbitals are filled with an electron, we can go back to the first orbital and insert the remaining electrons, this time in the opposite direction.

Note that in the case of nitrogen, 2 orbitals were fully filled and 3 were left with incomplete orbitals, as they have unpaired electrons.

This is because the s sublevel has one orbital, which holds a maximum of 2 electrons, and the p sublevel has three orbitals, which can be filled with a maximum of 6 electrons.

question 5

Quantum numbers are like coordinates, which have the function of locating electrons in an atom's electrons. Each electron has a specific set of quantum numbers.

Correctly relate the quantum number (column 1) to its description (column 2).

(I) Principal Quantum Number
(II) Secondary quantum number
(III) Magnetic quantum number
(IV) Spin quantum number

( ) indicates the energy sublevel, that is, the energy sublevel to which the electron belongs.
( ) indicates the direction of rotation of the electron within an orbital.
( ) indicates the energy level, that is, the electronic shell in which the electron is.
( ) indicates the orbital where the electron is, that is, the region most likely to find it within an energy sublevel.

The correct sequence is:

a) I, II, III and IV
b) II, IV, I and III
c) III, I, IV and II
d) IV, III, II and I

see answer

Correct alternative: b) II, IV, I and III.

(II) The secondary quantum number indicates the energy sublevel, that is, the energy sublevel to which the electron belongs.

(IV) The spin quantum number indicates the rotation sense electron within an orbital.

(I) The principal quantum number indicates the energy level, that is, the electronic shell in which the electron is.

(III) The magnetic quantum number indicates the orbital where the electron is, that is, the region most likely to find it within an energy sublevel.

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question 6

The principal “n”, secondary “l” and magnetic “m” quantum numbers of the most energetic electron of the iron atom (Z = 26) are, respectively:

a) 2, 2, -2
b) 3, 1, 2
c) 1, -3, 2
d) 3, 2, -2

see answer

Correct alternative: d) 3, 2, -2.

The first step to answer this question is to make the electronic distribution of the iron atom. Since its atomic number is 26, the atom has 26 protons and, consequently, 26 electrons.

Electronic distribution of iron: 1s²2s²2p⁶ 3s²3p⁶4s²3d⁶

From this, we can extract the following observations:

• Taking into account that its most energetic electron is in shell 3, then n = 3;
• Its sublevel is d, so l = 2;
• The d sublevel has 5 orbitals. When distributing the electrons, the last one is in the -2 orbital, so m = -2.

Therefore, the correct alternative is d) 3, 2, -2.

question 7

According to the number of subatomic particles, atoms of chemical elements can be classified into

Isotopes: atoms of the same chemical element and, therefore, have the same atomic number (Z).
Isobars: atoms of different chemical elements that have the same mass number (A).
Isotones: atoms of different chemical elements that have the same number of neutrons (n).

Based on the above information, judge the following alternatives.

I. ₁₇³⁷cl and ₂₀⁴⁰Ca are isotones
II. ₂₀⁴⁰ca and ₁₈⁴⁰air are isobars
III. ₁¹H and ₁²H are isotopes

The statements are correct.

a) I and II
b) II and III
c) I and III
d) All alternatives

see answer

Correct alternative: d) All alternatives.

I. CORRECT. The elements ₁₇³⁷cl and ₂₀⁴⁰Ca are isotones because they have the same number of neutrons and different mass numbers and atomic numbers.

The mass number is calculated by adding the protons and neutrons (A= p + n). From this information, we can calculate the number of neutrons as follows:

Element A: ₁₇³⁷cl

A = p + n
37 = 17 + n
37 - 17 = n
20 = no

Element B: ₂₀⁴⁰Here

A = p + n
40 = 20 + n
40 - 20 = n
20 = no

II. CORRECT. The elements ₂₀⁴⁰ca and ₁₈⁴⁰Ar are isobars since they have the same mass number and different atomic numbers;

III. CORRECT. The elements ₁¹H and ₁²H are isotopes because they have the same atomic number and different mass numbers.

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question 8

(UFU-MG) Dalton, Thomson, Rutherford and Bohr are scientists who contributed significantly to the development of atomic theory.

Regarding the atomic structure, mark with (T) the true alternative(s) and with (F) the false(s).

1. ( ) Dalton postulated, based on experimental evidence, that the atom was an extremely small, massive and indivisible “ball”.
2. ( ) The results of experiments on electrical discharges in rarefied gases allowed Thomson to propose an atomic model consisting of negative and positive charges.
3. ( ) Experiments in bombardment of a gold plate with alpha particles led Rutherford to propose an atomic model in which the atom was made up of a nucleus and an electrosphere of equal sizes.
4. ( ) The interpretation of studies with hydrogen spectra led Bohr to propose that the atom has orbits defined by certain energies.
5. ( ) In Bohr's atomic model, the various energy states for electrons were called energy layers or levels.

The correct sequence is:

a) V, V, F, V, V
b) F, V, F, V, V
c) V, V, F, F, F
d) V, F, F, V, V
e) F, V, F, V, F

see answer

Correct Answer: a) T, T, F, T, T.

Atomic models were developed by scientists in an attempt to unravel the constitution of matter and study the composition of the atom.

1. TRUE. Dalton postulated, based on experimental evidence, that the atom was an extremely small, massive, permanent, and indivisible “ball”. Therefore, according to the scientist, atoms could neither be created nor destroyed.

2. TRUE. The results of experiments on electrical discharges in rarefied gases allowed Thomson to propose an atomic model consisting of negative and positive charges. His atomic model became known as "plum pudding", because, according to him, electrons were fixed on the surface of the positively charged atom.

3. FALSE. Experiments in bombardment of a gold plate with alpha particles led Rutherford to propose an atomic model in which the atom it was made up of a nucleus, positively charged, and concentrated in an extremely small volume, unlike the electrosphere.

4. TRUE. The interpretation of studies with hydrogen spectra led Bohr to propose that the atom has orbits defined by certain energies and electrons move in these layers around the core.

5. TRUE. In Bohr's atomic model, the different energy states for electrons were called energy layers or levels because they have specific energy values. Therefore, when an electron goes to a level more external to the electron, it must absorb energy. Upon returning to a shell closer to the nucleus, the electron then releases energy.

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question 9

(UFSC) The word atom originates from the Greek and means indivisible, that is, according to the Greek philosophers, the atom would be the smallest particle of matter that could not be further divided. Currently, this idea is no longer accepted.

Regarding atoms, it is true to say that:

01. cannot be disintegrated.
02. are made up of at least three fundamental particles.
04. have positive particles called electrons.
08. have two distinct regions, the nucleus and the electron.
16. have electrons whose electrical charge is negative.
32. contain uncharged particles called neutrons.

The sum of true statements is:

a) 56
b) 58
c) 62
d) 63

see answer

Correct alternative: a) 56.

01. FALSE. This idea was defended by the Greeks at the beginning of the study of atoms.

02. FALSE. The most known particles of the atom are: protons, electrons and neutrons. However, today it is known that protons and neutrons are formed by even smaller particles, the quarks.

04. FALSE. Protons are endowed with a positive charge.

08. TRUE. The nucleus is a small, central region of the atom where protons and neutrons are located. In the electrosphere are electrons moving around the nucleus.

16. TRUE. Electrons have a negative charge and are located in the atom's electrons.

32. TRUE. Neutrons are subatomic particles that have mass, but the electrical charge is practically zero.

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question 10

(Ufscar-SP) A relatively simple model for the atom describes it as being constituted by a nucleus containing protons and neutrons, and electrons revolving around the nucleus.

One of the isotopes of the element iron is represented by the symbol ₂₆⁵⁶Faith. In some compounds, such as blood hemoglobin, iron is in the 2+ oxidation state (Fe²⁺). Considering only the mentioned isotope, it is correct to state that in the Fe ion²⁺:

a) the number of neutrons is 56, the number of protons is 26 and the number of electrons is 24.
b) the number of neutrons + protons is 56 and the number of electrons is 24.
c) the number of neutrons + protons is 56 and the number of electrons is 26.
d) the number of protons is 26 and the number of electrons is 56.
e) the number of neutrons + protons + electrons is 56 and the number of protons is 28.

see answer

Correct alternative: b) the number of neutrons + protons is 56 and the number of electrons is 24.

The +2 oxidation state indicates that the iron atom, which in the ground state contains 26 electrons, has lost 2 electrons and, therefore, the number of electrons in the Fe ion²⁺ é 24.

The mass number is the sum of the number of protons and neutrons, which in the case of iron is 56.

Keep testing your knowledge with:

• Exercises on atoms
• Exercises on atomic models
• Exercises on electronic distribution
• Periodic table exercises
• Exercises on organizing the periodic table

Bibliographic references

ATKINS, P.W.; JONES, Loretta. Principles of chemistry: questioning modern life and the environment. 3.ed. Porto Alegre: Bookman, 2006.

BROWN, Theodore; LEMAY, H. Eugene; BURSTEN, Bruce E. Chemistry: the core science. 9 ed. Prentice Hall, 2005.

USERCO, João; Salvador, Edgard. General chemistry. 12th ed. Sao Paulo: Saraiva, 2006.

• Atom
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• Evolution of atomic models
• Atomic Structure
• Quantum Numbers: Major, Minor, Magnetic and Spin
• Exercises on the Periodic Table
• Radioactivity: what it is, types, laws and exercises