(a)(i) 1. State the periodic law.
2. What is meant by the term periodic property of elements?
(ii) List three properties of an element which show periodicity.
(iii) Explain briefly how each of the properties listed in (a)(i) in varies across the period.
(b) Defulle relative atomic mass.
(c)(i) What phenomenon is exhibited by an element Z which exist as \(^{35}_{17}Z\) and \(^{37}_{17}X\)
(ii) What accounts for the difference in the mass numbers of the element Z?
(iii) Calculate the relative atomic mass of Z if the percentage abundance of \(^{37}_{17}Z\) is 75%
(d)(i) State the method used for collecting each of the following gases: I. CO II. HCI III. H\(_2\)
(ii) Give a reason for your answer stated in (d)(i) I and II
(a)(i) 1. The periodic law states that the properties of elements are a periodic function of their atomic numbers.
2. A periodic property is a property of elements that recurs at regular intervals (varies gradually and repeatedly) when the elements are arranged in order of increasing atomic number.
(ii) Three properties showing periodicity: atomic radius, ionization energy, electronegativity.
(iii) Across a period from left to right:
- Atomic radius decreases - the increasing nuclear charge pulls the electrons in the same shell closer.
- Ionization energy increases - electrons are held more firmly by the greater nuclear charge.
- Electronegativity increases - the atom attracts a shared electron pair more strongly.
(b) Relative atomic mass is the ratio of the average mass of one atom of an element to one-twelfth of the mass of one atom of carbon-12.
(c)(i) The phenomenon is isotopy (Z exists as isotopes).
(ii) The difference in mass number is due to a different number of neutrons in the nuclei (17 protons each, but different neutron counts).
(iii) With 75% of \(^{37}Z\) and 25% of \(^{35}Z\):
\[\text{RAM} = \frac{(37 \times 75) + (35 \times 25)}{100} = \frac{2775 + 875}{100} = 36.5\]
(d)(i)
- I. CO - collected over water.
- II. HCl - collected by downward delivery (upward displacement of air).
- III. H2 - collected over water (or by downward displacement of water).
(ii) CO is collected over water because it is insoluble in water. HCl is collected by downward delivery of air because it is very soluble in water and is denser than air.
(a)(i) 1. The periodic law states that the properties of elements are a periodic function of their atomic numbers.
2. A periodic property is a property of elements that recurs at regular intervals (varies gradually and repeatedly) when the elements are arranged in order of increasing atomic number.
(ii) Three properties showing periodicity: atomic radius, ionization energy, electronegativity.
(iii) Across a period from left to right:
- Atomic radius decreases - the increasing nuclear charge pulls the electrons in the same shell closer.
- Ionization energy increases - electrons are held more firmly by the greater nuclear charge.
- Electronegativity increases - the atom attracts a shared electron pair more strongly.
(b) Relative atomic mass is the ratio of the average mass of one atom of an element to one-twelfth of the mass of one atom of carbon-12.
(c)(i) The phenomenon is isotopy (Z exists as isotopes).
(ii) The difference in mass number is due to a different number of neutrons in the nuclei (17 protons each, but different neutron counts).
(iii) With 75% of \(^{37}Z\) and 25% of \(^{35}Z\):
\[\text{RAM} = \frac{(37 \times 75) + (35 \times 25)}{100} = \frac{2775 + 875}{100} = 36.5\]
(d)(i)
- I. CO - collected over water.
- II. HCl - collected by downward delivery (upward displacement of air).
- III. H2 - collected over water (or by downward displacement of water).
(ii) CO is collected over water because it is insoluble in water. HCl is collected by downward delivery of air because it is very soluble in water and is denser than air.
