Atomic Structure Isotopes And Atomic Mass

1. What is the definition of 1 amu (atomic mass unit)?

1/10 the mass of one C-12 atom

1/12 the mass of one C-12 atom

1/6 the mass of one C-12 atom

The mass of one hydrogen atom

An atomic mass unit (amu) is defined as one twelfth of the mass of a carbon-12 (C-12) atom. This standard was established to provide a consistent reference for measuring atomic masses of different elements. Since carbon-12 is a stable isotope and is widely used in scientific calculations, defining the amu in relation to its mass allows for easier comparisons and calculations in chemistry and physics, facilitating a universal understanding of atomic weights across various elements.

Explanation

An atomic mass unit (amu) is defined as one twelfth of the mass of a carbon-12 (C-12) atom. This standard was established to provide a consistent reference for measuring atomic masses of different elements. Since carbon-12 is a stable isotope and is widely used in scientific calculations, defining the amu in relation to its mass allows for easier comparisons and calculations in chemistry and physics, facilitating a universal understanding of atomic weights across various elements.

2. A hydrogen atom is 8.40% as massive as the standard C-12 atom. What is the relative atomic mass of hydrogen?

1.200 amu

0.840 amu

1.008 amu

1.080 amu

To find the relative atomic mass of hydrogen, we use the fact that the hydrogen atom is 8.40% as massive as the carbon-12 atom, which has a defined mass of 12 amu. Calculating 8.40% of 12 amu gives us 1.008 amu. This value reflects the mass of a hydrogen atom in atomic mass units (amu), making it the most accurate representation of hydrogen's relative atomic mass compared to the standard reference of carbon-12.

Explanation

To find the relative atomic mass of hydrogen, we use the fact that the hydrogen atom is 8.40% as massive as the carbon-12 atom, which has a defined mass of 12 amu. Calculating 8.40% of 12 amu gives us 1.008 amu. This value reflects the mass of a hydrogen atom in atomic mass units (amu), making it the most accurate representation of hydrogen's relative atomic mass compared to the standard reference of carbon-12.

3. Which of the following elements has the highest relative atomic mass according to Table 3.1?

Chlorine (Cl)

Sulfur (S)

Aluminum (Al)

Iron (Fe)

Iron (Fe) has the highest relative atomic mass among the listed elements. Relative atomic mass is a measure of the mass of an atom relative to one-twelfth of the mass of carbon-12. In this case, iron's atomic mass is approximately 55.85 u, which is greater than that of chlorine (35.45 u), sulfur (32.07 u), and aluminum (26.98 u). Therefore, when comparing these elements, iron stands out as the heaviest based on its atomic mass.

Explanation

Iron (Fe) has the highest relative atomic mass among the listed elements. Relative atomic mass is a measure of the mass of an atom relative to one-twelfth of the mass of carbon-12. In this case, iron's atomic mass is approximately 55.85 u, which is greater than that of chlorine (35.45 u), sulfur (32.07 u), and aluminum (26.98 u). Therefore, when comparing these elements, iron stands out as the heaviest based on its atomic mass.

4. In Fig. 3.1, the two isotopes of Neon differ in which of the following?

Number of protons

Number of electrons

Number of neutrons

Atomic number

Isotopes of an element have the same number of protons and electrons, which determine the element's identity and charge. However, they differ in the number of neutrons in their nuclei. This variation in neutron count leads to differences in atomic mass while maintaining the same atomic number, which defines the element as Neon. Thus, the distinction between the isotopes of Neon lies in the differing numbers of neutrons.

Explanation

Isotopes of an element have the same number of protons and electrons, which determine the element's identity and charge. However, they differ in the number of neutrons in their nuclei. This variation in neutron count leads to differences in atomic mass while maintaining the same atomic number, which defines the element as Neon. Thus, the distinction between the isotopes of Neon lies in the differing numbers of neutrons.

5. Isotopes are atoms of the same element that have the same atomic number but different ____.

Isotopes are variations of a particular chemical element that have the same number of protons, which defines the element, but differ in the number of neutrons. This difference in neutron count leads to variations in their mass, resulting in different mass numbers. Therefore, while isotopes maintain the same chemical properties due to their identical atomic structure, their physical properties, such as stability and radioactivity, can vary significantly because of their differing mass numbers.

Explanation

Isotopes are variations of a particular chemical element that have the same number of protons, which defines the element, but differ in the number of neutrons. This difference in neutron count leads to variations in their mass, resulting in different mass numbers. Therefore, while isotopes maintain the same chemical properties due to their identical atomic structure, their physical properties, such as stability and radioactivity, can vary significantly because of their differing mass numbers.

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6. The word 'isotope' was coined by Soddy and comes from the Greek words 'isos' and 'tope'. What do these words mean respectively?

Different and number

Same and place

Equal and mass

Same and element

The term 'isotope' combines the Greek words 'isos,' meaning 'same,' and 'topos,' meaning 'place.' This reflects the concept that isotopes of an element occupy the same position on the periodic table but have different mass numbers due to varying numbers of neutrons. Thus, while they share the same chemical properties and belong to the same element, their physical properties, such as mass, differ. This terminology emphasizes the relationship between isotopes in terms of their identity and location in the context of atomic structure.

Explanation

The term 'isotope' combines the Greek words 'isos,' meaning 'same,' and 'topos,' meaning 'place.' This reflects the concept that isotopes of an element occupy the same position on the periodic table but have different mass numbers due to varying numbers of neutrons. Thus, while they share the same chemical properties and belong to the same element, their physical properties, such as mass, differ. This terminology emphasizes the relationship between isotopes in terms of their identity and location in the context of atomic structure.

7. Isotopes are chemically alike but differ in their physical properties.

True

False

Isotopes are variants of the same chemical element that have the same number of protons but different numbers of neutrons. This means they have identical chemical properties since these properties are determined by the electron configuration, which remains unchanged. However, their differing neutron counts lead to variations in physical properties such as mass and stability. For instance, heavier isotopes may have different rates of diffusion or boiling points compared to their lighter counterparts. Thus, while isotopes behave similarly in chemical reactions, their physical characteristics can vary significantly.

Explanation

Isotopes are variants of the same chemical element that have the same number of protons but different numbers of neutrons. This means they have identical chemical properties since these properties are determined by the electron configuration, which remains unchanged. However, their differing neutron counts lead to variations in physical properties such as mass and stability. For instance, heavier isotopes may have different rates of diffusion or boiling points compared to their lighter counterparts. Thus, while isotopes behave similarly in chemical reactions, their physical characteristics can vary significantly.