Atomic Structure

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Question 1

Which statement is correct about the isotopes of an element?

They have the same mass number.

They have the same number of protons and neutrons in the nucleus.

They have the same electron arrangement or configuration.

They have more protons than neutrons.

Wrong Answer!Isotopes are 2 or more atoms of the same element with different number of neutrons (and therefore different relative isotope masses). They have the same numbers of protons and hence the same number of electrons.

the compound H2X [2H+X2-]

Question 2A chemical element with the symbol X has the

electron arrangement 2,8,6. Which chemical species is this chemical element most likely to form?

the ion X3+ the ion X6+

the compound XF8[X8+ 8F-]

Wrong Answer!H2S : [2H+X2-]

I and II only

Question 3

Which of the following particles contains more electrons than neutrons?

I. II. III.

I only II only

II and III only

11H

3517Cl

3919K

Wrong Answer!i. 1p 1e 0n

ii. 17p 18e 18n

iii. 19p 18e 20n

Question 4

What information about the structure of a helium atom can be gained from its emission spectrum?

Most of the mass of the atom is in its nucleus.

The electrons may exist in any of several energy levels.

A helium atom contains two electrons and two protons.

The electrons in the helium atom are held near the nucleus.

Wrong Answer!Emission spectra provide evidence that electrons exist in fixed energy levels within an atom.

Question 5

What is the correct number of each particle in a fluoride ion, 19F- ?

Note :

p represents protons; n represents neutrons ; e represents electrons

9p , 10n , 8e 9p , 10n , 9e

9p , 19n , 10e9p , 10n , 10e

Wrong Answer!9 protons (from periodic table) ; 10 electrons in the atom ( due to the single negative charge) and 10 neutrons (19-9)

2

Question 6

How many valence electrons are present in the element of atomic number 14?

4 3

1

Wrong Answer!The element is Silicon with the element arrangement 2,8,4

Question 7Which statement is correct about a line emission

spectrum?

Electrons neither absorb nor release energy as they move from low to high energy levels.

Electrons absorb energy as they move from high to low energy levels.

Electrons release energy as they move from high to low energy levels.

Electrons release energy as they move from low to high energy levels.

Wrong Answer!Electrons release energy as they move from high to low energy levels. Light is released.

Question 8

What fraction of a radioisotope will remain after three half-lives?

1/16 1/3

3/41/8

Wrong Answer!1 ½ ¼ 1/8

Question 9

A particular element consists of two isotopes: 72% of mass number 85 and 28% of mass number 87. What is the expected range of the relative atomic mass?

Less than 85 Between 85 and 86

More than 88Between 86 and 87

Wrong Answer!Relative atomic mass is a weighted average. The more abundant isotope has a mass number of 85.

72% x 85 + 28% x 87

Question 10

Which is the correct sequence for some of the various stages that typically occur in the analysis of an element during mass spectrometry?

Electron bombardment, vaporization, acceleration, deflection, detection.

Vaporization, electron bombardment, acceleration, deflection, detection.

Deflection, acceleration, electron bombardment, vaporization, detection.

Vaporization, electron bombardment, deflection, acceleration, detection.

Wrong Answer!The sample is first vaporized by lowering the surrounding pressure. A mass spectrometer can only accept gaseous atoms or molecules. The molecules or atoms are then subjected to bombardment by high energy electrons which remove the valence electron to form unipositive ions. The ions are then accelerated by an electric field before entering a powerful magnetic field where they experience deflection according to their mass-to-charge ratio.

Question 11The atomic numbers and mass numbers for four

different nuclei are given in the table below. Which two are isotopes?

Atomic number Mass number

I 101 258

II 102 258

III 102 260

IV 103 259

I and II II and III

I and IVIII and IV

Wrong Answer!I. 157 neutrons

II. 156 neutrons

III. 158 neutrons

IV. 156 neutrons

n = 3 n = 5

Question 12Which electronic transition within a hydrogen atom

requires the greatest energy?

n = 1 n = 2 n = 2 n = 3

n = 5 n = ∞

Wrong Answer!Energy levels rapidly converge with an increase in n.

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