Ch.2 - Atoms, Molecules, and Ions

Problem 99b

Chapter 2, Problem 99b

It is common in mass spectrometry to assume that the mass of a cation is the same as that of its parent atom. (b) What percentage of the mass of an 1H atom does the electron represent?

Verified step by step guidance

Step 1: The mass of a hydrogen atom (1H) is approximately 1.007825 amu (atomic mass units). This includes the mass of the proton and the electron.

Step 2: The mass of an electron is approximately 0.0005486 amu.

Step 3: To find the percentage of the mass that the electron represents, you need to divide the mass of the electron by the mass of the hydrogen atom and then multiply by 100.

Step 4: The formula to calculate the percentage is: (mass of electron / mass of hydrogen atom) * 100.

Step 5: Substitute the given values into the formula and calculate the percentage. Remember, you are not required to calculate the final result, just understand the steps to get to the solution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mass Spectrometry

Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions. It allows for the identification and quantification of different substances based on their mass. In this context, it is important to understand that the mass of ions, such as cations, is often approximated by the mass of their parent atoms, neglecting the mass of electrons due to their relatively small contribution.

Atomic Mass and Electron Mass

The atomic mass of an element is primarily determined by the mass of its protons and neutrons, as electrons contribute negligibly to the overall mass. For hydrogen (1H), the mass of the electron is about 1/1836 of the mass of a proton. This significant difference highlights the minimal impact of electrons on the total mass of an atom, which is crucial for calculations in mass spectrometry.

Percentage Calculation

To find the percentage of the mass of an atom that is due to its electron, one can use the formula: (mass of electron / mass of atom) × 100%. For hydrogen, this involves comparing the mass of the electron (approximately 9.11 x 10^-31 kg) to the mass of the hydrogen atom (approximately 1.67 x 10^-27 kg). This calculation illustrates the relative insignificance of the electron's mass in the context of the entire atom.

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Textbook Question

There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of Br₂ molecules, and the mass of a Br2 molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of Br₂ consists of three peaks: Mass (u) Relative Size 157.836 0.2569 159.834 0.4999 161.832 0.2431 (c) Determine the average molecular mass of a Br₂molecule.

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Textbook Question

There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of Br₂ molecules, and the mass of a Br₂ molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of Br₂ consists of three peaks: Mass (u) Relative Size 157.836 0.2569 159.834 0.4999 161.832 0.2431 (d) Determine the average atomic mass of a bromine atom

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Textbook Question

There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of Br₂ molecules, and the mass of a Br₂ molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of Br₂ consists of three peaks: Mass (u) Relative Size 157.836 0.2569 159.834 0.4999 161.832 0.2431 (e) Calculate the abundances of the two isotopes. Calculate the abundance of the heavier isotope.

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Textbook Question

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Textbook Question

The first atoms of seaborgium (Sg) were identified in 1974. The longest-lived isotope of Sg has a mass number of 266. (a) How many protons, electrons, and neutrons are in an ²⁶⁶Sg atom?

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Textbook Question

The first atoms of seaborgium (Sg) were identified in 1974. The longest-lived isotope of Sg has a mass number of 266. (b) Atoms of Sg are very unstable, and it is therefore difficult to study this element's properties. Based on the position of Sg in the periodic table, what element should it most closely resemble in its chemical properties?

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