Nuclei Flashcards
What is the overall structure of a nucleus?
The nucleus is the central part of an atom where the positive charge and mass are densely concentrated. It is much smaller in size compared to the atom and contains most of the atom’s mass.
What experiments demonstrated the small size of the nucleus compared to the atom?
Experiments on the scattering of alpha particles showed that the radius of a nucleus was smaller than the radius of an atom by a factor of about 10^4.
What is the ratio of the volume of a nucleus to the volume of an atom?
The volume of a nucleus is about 10^-12 times the volume of an atom.
If an atom were enlarged to the size of a classroom, what would be the relative size of the nucleus?
The nucleus would be approximately the size of a pinhead.
What percentage of the mass of an atom is contained within the nucleus?
More than 99.9% of the mass of an atom is concentrated within its nucleus.
Does the nucleus have a structured composition? If so, what are its constituents?
Yes, the nucleus has a structured composition. It consists of protons and neutrons, collectively known as nucleons.
How are the constituents of the nucleus held together?
The constituents of the nucleus, protons, and neutrons, are held together by the strong nuclear force.
What is the mass of a carbon atom, and why is the atomic mass unit (u) used instead of kilograms?
The mass of a carbon atom is 1.992647 × 10^−26 kg. The atomic mass unit (u) is used because the mass of an atom is very small, making kilograms inconvenient for measurement.
Define the atomic mass unit (u) and explain its relationship with the mass of a carbon-12 atom.
The atomic mass unit (u) is defined as 1/12th of the mass of a carbon-12 atom. Therefore, the mass of one carbon-12 atom is equivalent to 12 u.
What are isotopes, and how do they differ from one another?
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. They exhibit identical chemical properties but have different masses.
How are atomic masses accurately measured, and what instrument is used?
Atomic masses are measured accurately using a mass spectrometer.
Explain the concept of isotones and provide an example.
Isotones are nuclides with the same neutron number but different atomic numbers. An example is 198^80Hg and 197^79Au.
Who discovered the neutron, and how was it verified?
The neutron was discovered by James Chadwick in 1932. Its existence was verified through the emission of neutral radiation observed when beryllium nuclei were bombarded with alpha particles.
What is the composition of a nucleus, and what terms and symbols are used to describe it?
The composition of a nucleus includes protons and neutrons. Terms and symbols used to describe it include:
Z (atomic number) = number of protons
N (neutron number) = number of neutrons
A (mass number) = total number of protons and neutrons
Describe the properties of a proton and its significance in atomic structure.
A proton carries one unit of fundamental charge and is stable. It determines the atomic number of an element and is located in the nucleus.
Why are neutrons necessary in atomic nuclei, and who discovered them?
Neutrons are necessary in atomic nuclei to account for the observed mass of isotopes. James Chadwick discovered neutrons in 1932.
What is the stability of a free neutron, and how does it decay?
A free neutron is unstable and decays into a proton, an electron, and an antineutrino with a mean life of about 1000 seconds. However, it is stable inside the nucleus.
What is the mass of a carbon atom expressed in kilograms and atomic mass units (u)?
The mass of a carbon atom is approximately 1.992647×10^−26kg and 12 u.
Define the atomic mass unit (u) and its relationship with the mass of a carbon-12 atom.
The atomic mass unit (u) is defined as 1/12th of the mass of a carbon-12 atom. It is used to express atomic masses conveniently.
What is the significance of the atomic mass of chlorine being 35.46 u?
The atomic mass of chlorine being 35.46 u illustrates an exception to the general trend where atomic masses of various elements are close to integral multiples of the mass of a hydrogen atom.
What are isotopes, and how are they identified?
Isotopes are atomic species of the same element that have the same chemical properties but differ in mass. They are identified through the measurement of atomic masses using a mass spectrometer.
Explain the concept of average atomic mass using chlorine as an example.
The average atomic mass of chlorine is calculated as a weighted average of the masses of its isotopes, considering their relative abundances. For chlorine, it is approximately 35.47 u.
What are the three isotopes of hydrogen, and what are their respective masses?
The three isotopes of hydrogen are protium (1.0078 u), deuterium (2.0141 u), and tritium (3.0160 u).
Describe the composition of the nucleus in terms of protons, neutrons, and atomic number (Z).
The nucleus contains protons and neutrons, where the number of protons is equal to the atomic number (Z), and the mass number (A) is the sum of protons and neutrons.
Explain the discovery of the neutron and its significance.
The neutron was discovered by James Chadwick in 1932. Its existence was confirmed through experiments involving the bombardment of beryllium nuclei with alpha particles, leading to the emission of neutral radiation. Chadwick’s discovery was significant as it provided insight into the composition of atomic nuclei.
What is the mass of a neutron, and why is it considered stable inside the nucleus?
The mass of a neutron is approximately 1.00866 u or 1.6749×10 −27kg. Neutrons are considered stable inside the nucleus due to the strong nuclear force that binds them with protons.
Define atomic number (Z), neutron number (N), and mass number (A), and explain their significance in describing nuclear species.
Atomic number (Z) represents the number of protons, neutron number (N) represents the number of neutrons, and mass number (A) is the sum of protons and neutrons. These parameters help in identifying different isotopes and nuclides of an element.
Who was the pioneer credited with postulating the existence of the atomic nucleus?
Rutherford.
What experiment did Geiger and Marsden perform at Rutherford’s suggestion?
The scattering of alpha particles from thin gold foils.
What was the distance of closest approach to a gold nucleus for an alpha particle with a kinetic energy of 5.5 MeV?
Approximately 4.0 × 10^(-14) m.