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2022/23 Academic Year Chemistry Review Exercise for Grade 9

Review questions
Unit Three- structure of an atom
I. Choose the best answer from the alternatives given below and mark
your answers
1. Which of the following has a positive charge?
a. proton d. electron
b. neutron e. atom
c. anion
2. Rutherford carried out experiments in which a beam of alpha particles was directed at a thin
piece of gold foil. From these experiments he concluded that:
a. Electrons are massive particles.
b. The positively charged parts of atoms are moving about with a velocity approaching the speed of
light.
c. The positively charged parts of atoms are extremely small and extremely heavy particles.
d. The diameter of an electron is approximately equal to that of the nucleus.
e. Electrons travel in circular orbits around the nucleus.
3. Consider the species 72Zn, 75As and 74Ge. These species have:
a. The same number of electrons.
b. The same number of protons.
c. The same number of neutrons.
d. The same number of protons and neutrons.
e. The same mass number.
4. The neutral atoms of all of the isotopes of the same element have
a. Different numbers of protons.
b. Equal numbers of neutrons.
c. The same number of electrons.
d. The same mass numbers.
e. The same masses.
5. What is the atomic weight of a hypothetical element consisting of two isotopes, one with mass
= 64.23 amu (26.0%), and one with mass = 65.32 amu?
a. 65.3 amu d. 65.0 amu
b. 64.4 amu e. 64.8 amu
c. 64.9 amu
6. Naturally occurring rubidium consists of just two isotopes. One of the isotopes consists of atoms having
a mass of 84.912 amu; the other of 86.901 amu. What is the percent natural abundance of the heavier
isotope?
a. 15% b. 28%
7. Which of the responses contains all the statements that are consistent with the Bohr Theory of the atom
(and no others)?
i. An electron can remain in a particular orbit as long as it continually absorbs radiation of a definite
frequency.
ii. The lowest energy orbits are those closest to the nucleus.

“ፈጣሪ የምንወዳቸውን ልጆቻችንን ፣ ሀገራችንን እና ህዝባችንን ይጠብቅልን!”

Chemistry Review Exercise for Grade 9
 iii. An electron can jump from the K shell (n = 1 major energy level) to the M shell (n = 3 major
energy level) by emitting radiation of a definite frequency.

a. i, ii, iii d. i, ii
b. ii only e. ii, iii
c. iii only
8. The ground state electron configuration for arsenic is:
a. [Ar] 4s2 4p13
b. [Kr] 4s2 4p1
c. 1s2 2s2 2p6 3s2 3p6 3d12 4s2 4p1
d. 1s2 2s2 2p6 3s2 3p6 4s2 3d8 4p5
e. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
9. Which of the following electron configurations is correct for nickel?
a. [Ar] 4s1 3d8 d. [Kr] 4s2 3d8
1 8
b. [Kr] 4s 4d e. [Ar] 4s2 3d8
c. [Kr] 4s1 3d8
10. The outer electronic configuration ns2np4 corresponds to which one of the following elements in its
ground state?
a. As d. Br
b. Ca e. S
c. Cr
11. How many p electrons are there in an atom of rubidium?
a. 12 d. 9
b. 18 e. 6
c. 24
12. A neutral atom of an element has 2 electrons in the first energy level, 8 in the second energy level and 8
in the third energy level. This information does not necessarily tell us:
a. The atomic number of the element.
b. Anything about the element's chemical properties.
c. The total number of electrons in s orbitals.
d. The total number of electrons in p orbitals.
e. The number of neutrons in the nucleus of an atom of the element.
13. According to John Dalton's observations, when elements combine in a compound,
a. The ratio of their masses is always the same.
b. Each element contributes an equal number of atoms.
c. Their volumes are always equal.
d. Their masses are always equal.
14. Rutherford's gold foil experiment provided evidence for which of the following?
a. There is a dense, positively charged mass in the center of an atom.
b. Gold is not as dense as previously thought
c. Alpha particles have a positive charge.
d. Negative and positive charges are spread evenly throughout an atom.
15. In an atomic model that includes a nucleus, positive charge is
a. Concentrated at multiple sites in an atom.
b. Located in the space outside the nucleus.
c. Spread evenly throughout an atom.
d. Concentrated in the center of an atom.
16. Which subatomic particle has a negative charge?
a. Neutron c. Electron
b. Proton d. Nucleus

“ፈጣሪ የምንወዳቸውን ልጆቻችንን ፣ ሀገራችንን እና ህዝባችንን ይጠብቅልን!”

Chemistry Review Exercise for Grade 9
17. Which statement about subatomic particles is true?
a. Neutrons have no charge and no mass.
b. An electron has far less mass then either a proton or a neutron.
c. Protons, neutrons, and electrons all have about the same mass.
d. Unlike protons or neutrons, electrons have no mass.
18. Which of the following is unique for any given element?
a. the number of protons c. the charge on the electrons
b. the number of neutrons d. the mass of the neutron
19. The number of protons in one atom of an element is the element's
a. mass number c. charge
b. isotope d. atomic number
20. To find the number of neutrons in an atom, you would subtract
a. atomic number from electron numer c. atomic number from mass number
b. mass number from atomic number d. isotope number from atomic number
21. In Niels Bohr's model of the atom, electrons move
a. Like planets orbiting the sun. c. Like popcorn in a popper.
b. Like beach balls on water waves. d. Like balls rolling down a hill.
22. What does the electron cloud model describe?
a. the precise location of electrons in an atom
b. the mass of the electrons in the atom
c. the most likely locations of electrons in an atom
d. the number of electrons in an atom
23. Which statement about alkali metals is correct?
a. they are located in the left-most column of the periodic table
b. they are extremely nonreactive
c. they form negative ions
d. they are usually gases
24. A mole is an SI base unit that describes the
a. mass of a substance c. volume of a substance
b. amount of a substance d. electric charge of a substance
25. Moving from left to right across a row of the periodic table, which of the following values increases by
exactly one from element to element?
a. atomic number c. isotope number
b. atomic mass unit d. mass number
26. The tendency of an element to react chemically is closely related to
a. how tightly atoms are packed in the element
b. the number of valence electrons in atoms of the element
c. its atomic mass
d. the ratio of protons to neutrons in atoms of the element
27. Which statement is true about oxygen-17 and oxygen-18?
a. They are isotopes of oxygen
b. they do not have the same number of protons
c. their masses are identical
d. They have the same mass number
28. In a periodic table, a set of properties repeats from
a. group to group c. element to element
b. column to column d. row to row
29. Which list of elements contains only metals?
a. sodium, chromium, copper c. helium, carbon, gold
b. iodine, iron, nickel d. phosphorus, nitrogen, oxygen

“ፈጣሪ የምንወዳቸውን ልጆቻችንን ፣ ሀገራችንን እና ህዝባችንን ይጠብቅልን!”

Chemistry Review Exercise for Grade 9
30. The usefulness of Mendeleev's periodic table was confirmed by
a. The discovery of elements with predicted properties.
b. The discovery of subatomic particles.
c. The discovery of the nucleus.
d. The immediate acceptance by other scientists.
31. An alkali metal has one valence electron, while an alkaline earth metal has
a. Two c. Four
b. Three d. none
32. As you move from left to right across a period, the number of valence electrons
a. increases then decreases c. increases
b. decreases d. stays the same
33. The standard on which the atomic mass unit is based is the mass of a
a. Neutron c. carbon-12 atom
b. chlorine-35 atom d. proton
34. The charge on an electron is
a. +1 c. -1
b. 0 d. -2
35. The relative mass of an electron to that of neutron is
a. 1 c. 1/18
b. 1/1840 d. 0
36. Valence electrons determine an atom's
a. Mass c. number of neutrons
b. chemical properties d. period
37. Ionization refers to the process of
a. changing from one period to another c. losing or gaining protons
b. losing or gaining electrons d. changing from lithium into fluorine
38. An atomic mass unit is equal to
a. one-fourth the mass of a lithium atom
b. one-fifteenth the mass of a nitrogen-15 atom
c. one-half the mass of a hydrogen atom
d. one-twelfth the mass of a carbon-12 atom
39. Which statement about noble gases is correct?
a. they are rare in nature
b. they are highly reactive
c. They exist as single elements rather than molecules
d. they can form compounds with bright colors
40. Semiconductors are elements that
a. are extremely hard
b. can conduct electric current only under certain conditions
c. have large atomic masses but small atomic numbers
d. do not form compounds
41. Carbon and other nonmetals are found in which area of the periodic table?
a. in the middle c. on the right
b. on the bottom d. on the left
42. Avogadro's constant in defined as the number of particles in
a. one gram of a pure substance c. one mole of a pure substance
b. one liter of a pure substance d. one kilogram of a pure substance.
43. How many protons are in an atom of bromine?
a. 172 c. 80
b. 79 d. 35
“ፈጣሪ የምንወዳቸውን ልጆቻችንን ፣ ሀገራችንን እና ህዝባችንን ይጠብቅልን!”
Chemistry Review Exercise for Grade 9
 44. Which of the following has a positive charge?
a. Electrons c. Neutrons
b. Protons d. None of the above

45. Neutrons and protons are collectively known as

a. Nucleons c. Atomic number
b. Mass number d. None of the above

46. The number of protons in an atom is equivalent to the number of

a. Neutrons c. Electrons
b. Protons d. None of the above

47. Name the scientist who was first to propose the atomic theory of an atom?
a. J. J. Thomson c. Neils Bohr
b. John Dalton d. None of the above

48. What was the source of alpha particles in the Rutherford scattering experiment?
a. Hydrogen nucleus c. Lithium nucleus
b. Helium nucleus d. None of the above
II. Answer the following questions accordingly
49. Is anything smaller than an atom?
50. What is an electron?
51. What is a proton?
52. What is a neutron?
53. Fill in the table.

Atomic number Mass number Number of protons Number of electrons Number of neutrons
2 – – 2 –
– 23 – – 11
– – 15 16 –
– 85 37 – –
53 – – 74 –
54. What is the limitation of Dalton’s Atomic Theory?
55. How do the atomic structures of an isotope range?
56. What are the postulates of Dalton’s Atomic Theory?
57. What are the limitations of Bohr’s atomic theory?
58. What is the significance of Rutherford’s atomic model?
59. What are the postulates of the Rutherford Atomic Model?
60. Explain how isotopes affect an element's average atomic mass.

“ፈጣሪ የምንወዳቸውን ልጆቻችንን ፣ ሀገራችንን እና ህዝባችንን ይጠብቅልን!”

Chemistry Review Exercise for Grade 9