Unit-3 Atomic Structure
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Unit-3 Atomic Structure
Answer: Most alpha particles passed straight through, showing the atom is mostly empty space.
Answer: The concentrated positive charge of the small, dense nucleus repelled the positive alpha particles at large angles.
Answer: Rutherford compared electrons revolving around the nucleus to planets revolving around the sun.
Answer: Because most alpha particles passed through undeflected, most of the atom is empty space.
Answer: Rutherford's model could not explain atomic stability; Bohr solved this by introducing fixed energy levels.
Answer: Bohr proposed that electrons move in fixed circular paths called orbits or shells.
Answer: The shells are named K, L, M, N starting from the nucleus outward.
Answer: The K shell is the first shell (n = 1) and can hold a maximum of 2 electrons.
Answer: The L shell is the second shell (n = 2) and can hold a maximum of 8 electrons.
Answer: The M shell is the third shell (n = 3), so 2 x 3^2 = 18 electrons maximum.
Answer: Shells are labelled K, L, M, N from the nucleus outward, so K is closest.
Answer: 2 x 2^2 = 2 x 4 = 8 electrons in the second shell.
Answer: The atomic number (Z) is the number of protons in the nucleus of an atom.
Answer: Z = A - n = 35 - 18 = 17 protons, so the atomic number is 17.
Answer: In a neutral atom, the number of electrons equals the atomic number, so there are 19 electrons.
Answer: Mass number = protons + neutrons = 12 + 12 = 24.
Answer: One amu is exactly 1/12 of the mass of one carbon-12 atom.
Answer: Isotopes have the same number of protons but different numbers of neutrons, so their mass numbers differ.
Answer: Chlorine exists mainly as Cl-35 (about 75%) and Cl-37 (about 25%).
Answer: Protium, deuterium and tritium are the three isotopes of hydrogen; helium is a different element.