(a) Consider the following table; (i) Which of the elements:
| Element |
Atomic Number |
Mass Number |
| J |
9 |
19 |
| Q |
13 |
27 |
| R |
16 |
32 |
| X |
19 |
39 |
| Y |
24 |
52 |
I. is a halogen?
II. is most likely to be attracted by a magnet?
III. belongs to group I?
IV. would readily form an ion with a double negative charge?
(ii) What type of bond would exist between J and X when they combine?
(iii) How many neutrons are there in Q?
(iv) Write the formula of the compound formed when R combines with X.
(v) State the element which exists as diatomic molecule..
(vi) Select the element which belong to the d-block of the periodic table.
(b)(i) Explain briefly the term atomic orbital
(ii) I. State three prostulates of Dalton's atomic theory.
II. List two limitations of this theory in the study of the atom
(iii) Describe briefly the structure of sodium chloride in its solid state.
(c) A sample of carbon is burnt at a rate of 0.50g per second for 30 minutes to generate heat.
(i) Write a balanced equation for the reaction
(ii) Determine the:
I. volume of carbon (IV) oxide produced at s.t.p.
II. moles of oxygen used up in the process at s.t.p. [C = 12.0, O = 16.0, Molar volume \(V_m\) = 22.4 dm\(^3\)].
Identify each element from its atomic number and mass number.
| Element | Atomic number | Mass number | Identity |
|---|
| J | 9 | 19 | Fluorine, F |
| Q | 13 | 27 | Aluminium, Al |
| R | 16 | 32 | Sulfur, S |
| X | 19 | 39 | Potassium, K |
| Y | 24 | 52 | Chromium, Cr |
(a)(i)
- I. Halogen: J (fluorine), a Group 7 element.
- II. Most likely attracted by a magnet: Y (chromium), a transition metal.
- III. Belongs to Group 1: X (potassium), configuration 2,8,8,1.
- IV. Readily forms an ion with a double negative charge: R (sulfur), which gains 2 electrons to form S2-.
(a)(ii) J is a Group 7 non-metal and X is a Group 1 metal, so they form an ionic (electrovalent) bond (potassium transfers one electron to fluorine, giving K+ and F-).
(a)(iii) Neutrons in Q:
\[\text{neutrons} = \text{mass number} - \text{atomic number} = 27 - 13 = \mathbf{14}\]
(a)(iv) R (S2-) combines with X (K+). Balancing charges gives K2S.
(a)(v) The element that exists as a diatomic molecule is J (fluorine, F2).
(a)(vi) The d-block element is Y (chromium).
(b)(i) An atomic orbital is a region in space around the nucleus of an atom where the probability of finding an electron is highest.
(b)(ii) I. Three postulates of Dalton's atomic theory:
- All matter is made up of tiny, indivisible particles called atoms.
- Atoms of the same element are identical in mass and chemical properties, while atoms of different elements differ.
- Atoms combine in simple whole-number ratios to form compounds, and atoms are neither created nor destroyed in a chemical reaction.
II. Two limitations of the theory:
- The atom is not indivisible; it is made up of smaller particles (protons, neutrons and electrons).
- Atoms of the same element are not always identical in mass, because of the existence of isotopes.
(b)(iii) In the solid state, sodium chloride has a giant ionic lattice. Na+ and Cl- ions are arranged alternately in a face-centred cubic structure, each Na+ surrounded by 6 Cl- ions and each Cl- surrounded by 6 Na+ ions (6:6 coordination), held together by strong electrostatic forces of attraction.
(c) Carbon burnt at 0.50 g per second for 30 minutes.
Total mass of carbon burnt:
\[m = 0.50\ \text{g s}^{-1} \times (30 \times 60)\ \text{s} = 0.50 \times 1800 = 900\ \text{g}\]
Moles of carbon:
\[n_C = \frac{900}{12.0} = 75\ \text{mol}\]
(i) Balanced equation:
\[\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)\]
(ii) I. From the equation, 1 mol C gives 1 mol CO2, so 75 mol C gives 75 mol CO2.
\[V_{CO_2} = 75\ \text{mol} \times 22.4\ \text{dm}^3\,\text{mol}^{-1} = \mathbf{1680\ dm^3}\]
II. From the equation, 1 mol C uses 1 mol O2, so:
\[n_{O_2} = 75\ \text{mol} \times \frac{1}{1} = \mathbf{75\ mol}\]
Identify each element from its atomic number and mass number.
| Element | Atomic number | Mass number | Identity |
|---|
| J | 9 | 19 | Fluorine, F |
| Q | 13 | 27 | Aluminium, Al |
| R | 16 | 32 | Sulfur, S |
| X | 19 | 39 | Potassium, K |
| Y | 24 | 52 | Chromium, Cr |
(a)(i)
- I. Halogen: J (fluorine), a Group 7 element.
- II. Most likely attracted by a magnet: Y (chromium), a transition metal.
- III. Belongs to Group 1: X (potassium), configuration 2,8,8,1.
- IV. Readily forms an ion with a double negative charge: R (sulfur), which gains 2 electrons to form S2-.
(a)(ii) J is a Group 7 non-metal and X is a Group 1 metal, so they form an ionic (electrovalent) bond (potassium transfers one electron to fluorine, giving K+ and F-).
(a)(iii) Neutrons in Q:
\[\text{neutrons} = \text{mass number} - \text{atomic number} = 27 - 13 = \mathbf{14}\]
(a)(iv) R (S2-) combines with X (K+). Balancing charges gives K2S.
(a)(v) The element that exists as a diatomic molecule is J (fluorine, F2).
(a)(vi) The d-block element is Y (chromium).
(b)(i) An atomic orbital is a region in space around the nucleus of an atom where the probability of finding an electron is highest.
(b)(ii) I. Three postulates of Dalton's atomic theory:
- All matter is made up of tiny, indivisible particles called atoms.
- Atoms of the same element are identical in mass and chemical properties, while atoms of different elements differ.
- Atoms combine in simple whole-number ratios to form compounds, and atoms are neither created nor destroyed in a chemical reaction.
II. Two limitations of the theory:
- The atom is not indivisible; it is made up of smaller particles (protons, neutrons and electrons).
- Atoms of the same element are not always identical in mass, because of the existence of isotopes.
(b)(iii) In the solid state, sodium chloride has a giant ionic lattice. Na+ and Cl- ions are arranged alternately in a face-centred cubic structure, each Na+ surrounded by 6 Cl- ions and each Cl- surrounded by 6 Na+ ions (6:6 coordination), held together by strong electrostatic forces of attraction.
(c) Carbon burnt at 0.50 g per second for 30 minutes.
Total mass of carbon burnt:
\[m = 0.50\ \text{g s}^{-1} \times (30 \times 60)\ \text{s} = 0.50 \times 1800 = 900\ \text{g}\]
Moles of carbon:
\[n_C = \frac{900}{12.0} = 75\ \text{mol}\]
(i) Balanced equation:
\[\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)\]
(ii) I. From the equation, 1 mol C gives 1 mol CO2, so 75 mol C gives 75 mol CO2.
\[V_{CO_2} = 75\ \text{mol} \times 22.4\ \text{dm}^3\,\text{mol}^{-1} = \mathbf{1680\ dm^3}\]
II. From the equation, 1 mol C uses 1 mol O2, so:
\[n_{O_2} = 75\ \text{mol} \times \frac{1}{1} = \mathbf{75\ mol}\]
