Atomic Structure Insights and Periodic Trends

1. Complete the table for Sulfur (S): How many protons, electrons, and neutrons does a neutral sulfur atom have, and what type of element is it?

Protons: 16, Electrons: 16, Neutrons: 16, Type: Non-metal

Protons: 16, Electrons: 16, Neutrons: 16, Type: Metal

Protons: 16, Electrons: 18, Neutrons: 16, Type: Non-metal

Protons: 32, Electrons: 32, Neutrons: 16, Type: Metalloid

A neutral sulfur atom has 16 protons and 16 electrons, which balance each other out, resulting in no overall charge. The number of neutrons can vary in isotopes, but the most common isotope of sulfur has 16 neutrons, making its atomic mass approximately 32. Sulfur is classified as a non-metal due to its properties, such as being a poor conductor of electricity and forming covalent bonds with other non-metals. This classification is consistent with its position in the periodic table, where it is found in group 16.

Explanation

A neutral sulfur atom has 16 protons and 16 electrons, which balance each other out, resulting in no overall charge. The number of neutrons can vary in isotopes, but the most common isotope of sulfur has 16 neutrons, making its atomic mass approximately 32. Sulfur is classified as a non-metal due to its properties, such as being a poor conductor of electricity and forming covalent bonds with other non-metals. This classification is consistent with its position in the periodic table, where it is found in group 16.

2. For the Magnesium ion (Mg²⁺), which of the following correctly describes its number of protons and electrons?

Protons: 12, Electrons: 12

Protons: 12, Electrons: 10

Protons: 10, Electrons: 12

Protons: 12, Electrons: 14

Magnesium has an atomic number of 12, indicating it has 12 protons. In its neutral state, it also has 12 electrons. However, the magnesium ion (Mg²⁺) has lost two electrons to achieve a positive charge. Therefore, the Mg²⁺ ion has 12 protons and 10 electrons, reflecting the loss of the two electrons that gives it a +2 charge. This results in an overall charge imbalance, confirming the identity of the magnesium ion.

Explanation

Magnesium has an atomic number of 12, indicating it has 12 protons. In its neutral state, it also has 12 electrons. However, the magnesium ion (Mg²⁺) has lost two electrons to achieve a positive charge. Therefore, the Mg²⁺ ion has 12 protons and 10 electrons, reflecting the loss of the two electrons that gives it a +2 charge. This results in an overall charge imbalance, confirming the identity of the magnesium ion.

3. With which noble gas is the magnesium ion (Mg²⁺) isoelectronic?

Helium (He)

Argon (Ar)

Neon (Ne)

Krypton (Kr)

Magnesium ion (Mg²⁺) has lost two electrons, resulting in an electron configuration similar to that of neon (Ne), which has a complete octet with 10 electrons. Isoelectronic species share the same number of electrons and thus similar electronic structures. In this case, both Mg²⁺ and Ne have 10 electrons, making them isoelectronic. Other noble gases like helium, argon, and krypton have different electron counts, so they do not match the electron configuration of Mg²⁺.

Explanation

Magnesium ion (Mg²⁺) has lost two electrons, resulting in an electron configuration similar to that of neon (Ne), which has a complete octet with 10 electrons. Isoelectronic species share the same number of electrons and thus similar electronic structures. In this case, both Mg²⁺ and Ne have 10 electrons, making them isoelectronic. Other noble gases like helium, argon, and krypton have different electron counts, so they do not match the electron configuration of Mg²⁺.

4. For Al-26, how many protons, electrons, and neutrons does this isotope have?

Protons: 13, Electrons: 13, Neutrons: 13

Protons: 26, Electrons: 26, Neutrons: 13

Protons: 13, Electrons: 13, Neutrons: 26

Protons: 13, Electrons: 13, Neutrons: 14

Al-26 is an isotope of aluminum, which has an atomic number of 13. This means it has 13 protons and, in a neutral atom, the same number of electrons, also 13. The mass number of Al-26 indicates the total number of protons and neutrons combined, which is 26. To find the number of neutrons, subtract the number of protons from the mass number: 26 - 13 = 13. Therefore, the isotope has 13 protons, 13 electrons, and 13 neutrons.

Explanation

Al-26 is an isotope of aluminum, which has an atomic number of 13. This means it has 13 protons and, in a neutral atom, the same number of electrons, also 13. The mass number of Al-26 indicates the total number of protons and neutrons combined, which is 26. To find the number of neutrons, subtract the number of protons from the mass number: 26 - 13 = 13. Therefore, the isotope has 13 protons, 13 electrons, and 13 neutrons.

5. In the beta decay of U-235, what particle is emitted?

Alpha particle (⁴₂He)

Beta particle (⁰₋₁e)

Gamma ray (γ)

Neutron (¹₀n)

In beta decay, a neutron in the nucleus of an unstable isotope transforms into a proton while emitting a beta particle, which is an electron (⁰₋₁e). This process increases the atomic number by one, resulting in the formation of a different element. In the case of U-235, this decay leads to the emission of a beta particle, distinguishing it from alpha decay, which emits an alpha particle, or gamma decay, which releases gamma rays. Thus, the emission of a beta particle is characteristic of this type of decay.

Explanation

In beta decay, a neutron in the nucleus of an unstable isotope transforms into a proton while emitting a beta particle, which is an electron (⁰₋₁e). This process increases the atomic number by one, resulting in the formation of a different element. In the case of U-235, this decay leads to the emission of a beta particle, distinguishing it from alpha decay, which emits an alpha particle, or gamma decay, which releases gamma rays. Thus, the emission of a beta particle is characteristic of this type of decay.

6. Antimony has two isotopes: Sb-121 (120.904 amu) and Sb-123 (122.904 amu), with an average atomic mass of 121.760 amu. What is the approximate percent abundance of Sb-121?

42.8%

57.2%

50.0%

72.0%

To find the percent abundance of Sb-121, we can set up an equation using the average atomic mass. Let x be the percent abundance of Sb-121, making the abundance of Sb-123 (100 - x). The equation based on the average atomic mass is:

\[ 120.904x + 122.904(100 - x) = 121.760 \]

Solving this equation yields x ≈ 57.2%. Thus, approximately 57.2% of antimony is Sb-121, indicating its significant presence compared to its other isotope.

Explanation

To find the percent abundance of Sb-121, we can set up an equation using the average atomic mass. Let x be the percent abundance of Sb-121, making the abundance of Sb-123 (100 - x). The equation based on the average atomic mass is:

\[ 120.904x + 122.904(100 - x) = 121.760 \]

Solving this equation yields x ≈ 57.2%. Thus, approximately 57.2% of antimony is Sb-121, indicating its significant presence compared to its other isotope.

7. Which of the following correctly arranges Cs, K, Rb, and Na in order of increasing atomic radius?

Cs < Rb < K < Na

Na < K < Rb < Cs

K < Na < Rb < Cs

Na < Rb < K < Cs

As you move down the alkali metal group in the periodic table, the atomic radius increases due to the addition of electron shells. Sodium (Na) has the smallest radius because it is higher up in the group, followed by potassium (K), rubidium (Rb), and cesium (Cs), which has the largest radius. This trend is consistent with the general properties of alkali metals, where the atomic size increases as you descend the group. Thus, the correct order of increasing atomic radius is Na < K < Rb < Cs.

Explanation

As you move down the alkali metal group in the periodic table, the atomic radius increases due to the addition of electron shells. Sodium (Na) has the smallest radius because it is higher up in the group, followed by potassium (K), rubidium (Rb), and cesium (Cs), which has the largest radius. This trend is consistent with the general properties of alkali metals, where the atomic size increases as you descend the group. Thus, the correct order of increasing atomic radius is Na < K < Rb < Cs.