5.1.2 The nucleus (3)
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1.
A certain element has an atomic number of 17 and a mass number of 35. State the number of protons and neutrons in a stable atom of this element. Explain how you determined your answer.
The element has 17 protons and 18 neutrons in a stable atom.
Explanation: The atomic number (17) directly corresponds to the number of protons in the nucleus of an atom. Therefore, a stable atom of this element must have 17 protons. The mass number (35) represents the total number of protons and neutrons. To find the number of neutrons, we subtract the number of protons from the mass number: 35 (mass number) - 17 (number of protons) = 18 neutrons. Therefore, a stable atom of this element has 17 protons and 18 neutrons.
2.
Define the terms proton number (atomic number, Z) and nucleon number (mass number, A). Explain the difference between them and their significance in identifying an element.
Proton Number (Atomic Number, Z): The number of protons in the nucleus of an atom. It is a defining characteristic of an element. The atomic number is unique to each element; changing the number of protons changes the element itself.
Nucleon Number (Mass Number, A): The total number of nucleons (protons and neutrons) in the nucleus of an atom. It is the sum of the proton number (Z) and the neutron number (N): A = Z + N
Difference and Significance: The atomic number (Z) determines the element's identity. The mass number (A) indicates the total mass of the nucleus and is related to the isotope of the element. Two isotopes of the same element have the same atomic number (Z) but different mass numbers (A) due to different numbers of neutrons.
3.
Explain, in terms of relative charges, why an atom is electrically neutral.
An atom is electrically neutral because it contains an equal number of protons and electrons. Protons have a positive relative charge (+1) and electrons have a negative relative charge (-1). The positive charge of the protons cancels out the negative charge of the electrons, resulting in a net charge of zero. Therefore, the overall charge of the atom is neutral.