1. (a) Distinguish between (6 marks) (i) Nucleon and nuclide (ii) Atomic number and Mass number (iii) An isotope and Avogadro's constant 2. (a)Which postulates of Dalton's atomic theory are strictly incorrect?Show why these errors didn't affect the apparent validity of the theory (3 marks) (a) State three observations that were made from the Rutherford's alpha -particle scattering experiment and what did these observations prove about the structure of an atom? (3 mark) 3. (a) (i) The element lead (Pb) consists of four naturally occurring isotopes with masses 203.97302,205.97444,206.97587 and 207.97663 a.m.u The relative abundances of these

1. (a) <br />(i) Nucleon: A nucleon is a term used to describe either a proton or a neutron, which are the particles found in the nucleus of an atom.<br />Nuclide: A nuclide is a specific type of atom characterized by the number of protons and neutrons in its nucleus. It is represented by the symbol of the element followed by the mass number (total number of protons and neutrons).<br /><br />(ii) Atomic number: The atomic number of an element is the number of protons in the nucleus of an atom. It determines the identity of an element and its position in the periodic table.<br />Mass number: The mass number of an atom is the total number of protons and neutrons in its nucleus. It is used to determine the relative mass of an atom.<br /><br />(iii) Isotope: An isotope is a variant of an element that has the same number of protons but a different number of neutrons in its nucleus. Isotopes of an element have the same chemical properties but different physical properties.<br />Avogadro's constant: Avogadro's constant, also known as Avogadro's number, is a fundamental constant in chemistry. It represents the number of particles (atoms, molecules, ions.) in one mole of a substance. The value of Avogadro's constant is approximately 6.022 x 10^23 particles per mole.<br /><br />2. (a) The postulates of Dalton's atomic theory that are strictly incorrect are:<br />- Atoms of the same element are identical in mass and properties.<br />- Atoms combine in simple whole-number ratios to form compounds.<br />- Atoms are indivisible and indestructible.<br /><br />These errors didn't affect the apparent validity of the theory because the theory was primarily focused on explaining chemical reactions and the formation of compounds. The inaccuracies in these postulates were later corrected with the discovery of isotopes and the development of modern atomic theory.<br /><br />3. (a) (i) The element lead (Pb) consists of four naturally occurring isotopes with masses 203.97302, 205.97444, 206.97587, and 207.97663 a.m.u. The relative abundances of these isotopes are as follows:<br />- 206.97587 a.m.u.: 1.4%<br />- 207.97663 a.m.u.: 22.7%<br />- 205.97444 a.m.u.: 1.5%<br />- 203.97302 a.m.u.: 72.2%<br /><br />To calculate the average atomic mass of lead, we can use the formula:<br /><br />Average atomic mass = (mass of isotope 1 x relative abundance of isotope 1) + (mass of isotope 2 x relative abundance of isotope 2) + (mass of isotope 3 x relative abundance of isotope 3) + (mass of isotope 4 x relative abundance of isotope 4)<br /><br />Substituting the given values, we get:<br /><br />Average atomic mass = (206.97587 x 0.014) + (207.97663 x 0.227) + (205.97444 x 0.015) + (203.97302 x 0.722)<br /><br />Calculating the above expression, we get the average atomic mass of lead as approximately 207.2 a.m.u.