Problem 1 - Biology of Humans: Concepts, Applications, and Issues

Question

Choose the incorrect statement: a. Electrons are found outside the nucleus at certain energy levels (shells). b. For any atom, the number of protons plus the number of electrons equals the atomic mass. c. The atomic number equals the number of protons in the nucleus. d. Electrons have negligible mass.

Step-by-Step Solution

Answer

The answer is b.

Step 1 Title - Understand the basic structure of an atom

Atoms consist of a nucleus containing protons and neutrons, with electrons orbiting this nucleus in specific energy levels or shells.

Step 2 Title - Verify the correctness of each statement

Analyze each statement based on known atomic theory principles. Confirm if electrons are found outside the nucleus in energy levels (Statement a).

Step 3 Title - Assess the second statement

Check if the number of protons plus the number of electrons equals the atomic mass (Statement b). This is incorrect since atomic mass is actually the sum of the number of protons and neutrons.

Step 4 Title - Evaluate the atomic number definition

Verify that the atomic number equals the number of protons in the nucleus (Statement c), which is a correct statement.

Step 5 Title - Examine the mass of electrons

Assess if electrons have negligible mass (Statement d). This is correct since the mass of electrons is so small it is often considered negligible.

Key Concepts

Protons

Protons are positively charged particles found in the nucleus of an atom. Each proton carries a charge of +1 and has a significant mass relative to electrons.

Protons are crucial because:

• They define the chemical element: The number of protons (atomic number) determines what element the atom is.
• They contribute to the atomic mass: The mass of a proton is roughly 1 atomic mass unit (amu).
• They work with neutrons to provide stability: Protons combined with neutrons form the nucleus's core, providing mass and stability to the atom.

When you change the number of protons in an atom, you fundamentally change the identity of the element. For example, hydrogen has one proton, which makes it hydrogen.

Electrons

Electrons are negatively charged particles that orbit the nucleus of an atom in specific energy levels or shells. Each electron carries a charge of -1 and has negligible mass compared to protons and neutrons.

Key points about electrons:

• They are found in energy levels or shells outside the nucleus.
• Electrons are involved in chemical reactions and bonding.
• The distribution of electrons among different energy levels determines the atom’s chemical properties.

Unlike protons and neutrons, electrons are much lighter, and their mass is considered negligible in most calculations. The number of electrons equals the number of protons in a neutral atom, meaning an atom has no overall charge.

Atomic Mass

Atomic mass is the weighted average mass of all the isotopes of an element. It is often measured in atomic mass units (amu).

Important details about atomic mass:

• It is approximately the sum of the number of protons and neutrons in the nucleus.
• Electrons do not significantly contribute to the atomic mass because their mass is negligible.
• Each isotope of an element has a different number of neutrons, thus affecting its atomic mass.

For example, the atomic mass of carbon is approximately 12 amu because it commonly has six protons and six neutrons, although isotopes can vary slightly in mass.

Atomic Number

The atomic number of an element is defined as the number of protons in the nucleus of an atom. It is a unique identifier for each chemical element.

Significance of the atomic number:

• It determines the element’s position in the periodic table.
• It equals the number of protons, which also equals the number of electrons in a neutral atom.
• Knowing the atomic number helps in understanding the element's chemical behavior and properties.

For example, the atomic number of oxygen is 8, meaning it has 8 protons in its nucleus. This number doesn't change whether the atom gains or loses neutrons or electrons, thus distinguishing it always as oxygen.