Unit-3 Atomic Structure
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Unit-3 Atomic Structure
Answer: Cations form when atoms lose electrons, giving a positive charge.
Answer: 12 - 2 = 10 electrons remain in the magnesium ion.
Answer: Aluminium loses three electrons, so the ion carries a +3 charge.
Answer: 13 - 3 = 10 electrons remain in the aluminium ion.
Answer: Mass number = 7 + 8 = 15 (nitrogen-15).
Answer: Isotopes have the same atomic number, which means the same number of protons.
Answer: Isotopes differ only in the number of neutrons, which changes their mass number.
Answer: Chemical properties depend on electrons, and isotopes have identical electron configurations.
Answer: Chemical behaviour is governed by the electrons in the outer shells, especially valence electrons.
Answer: 19 protons with 18 electrons gives a net +1 charge, so it is the potassium ion K+.
Answer: Bohr called the fixed circular paths of electrons shells or energy levels.
Answer: The outermost occupied shell is the valence shell and holds the valence electrons.
Answer: Valence electrons are those in the outermost shell; they determine chemical behaviour.
Answer: Oxygen's configuration is 2, 6, so it has 6 valence electrons in the L shell.
Answer: Chlorine's configuration is 2, 8, 7, so it has 7 valence electrons.
Answer: Cathode rays are emitted from the cathode and consist of electrons.
Answer: Canal rays are positively charged and are streams of protons.
Answer: In a neutral atom, protons equal electrons, so Z = 6, which is carbon.
Answer: Carbon has 6 electrons arranged as 2 in the K shell and 4 in the L shell, written 2, 4.
Answer: Average = (0.5 x 10) + (0.5 x 12) = 5 + 6 = 11 amu.