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[Word count: c. 950 words (not including diagrams and references)]
(a) Analysis of a Metal and a Non-Metal Element
1. A Metal: Iron (Fe), Atomic Number = 26
(i) Periodic Table Position and Electron Configuration
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
- Explanation: Iron (Fe) is in period 4, group 8 (or group 8B, in older notation).
- Period 4: Its outermost electron is in the fourth shell (n=4).
- Group 8: It possesses 8 electrons in the combination of its outermost s- and d-subshells (4s²3d⁶).
(ii) Bonding in Iron
- Type of bonding: Metallic bonding
- Explanation: Each iron atom releases some electrons into a "sea" of delocalized electrons, forming positive metal ions in a lattice. The electrostatic attraction between positive ions and the sea of electrons holds the metal together, making it conductive and malleable.
(iii) Formation of the Most Common Ions
- Common ions: Fe²⁺ and Fe³⁺
- Explanation: Iron can lose two 4s electrons to form Fe²⁺:
Fe (1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶) → Fe²⁺ (1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶)
- Can also lose an additional 3d electron for Fe³⁺:
Fe → Fe³⁺ (1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵)
- This occurs during reactions such as with acids or oxygen ([Housecroft, 2012]).
2. A Non-metal: Sulfur (S), Atomic Number = 16
(i) Periodic Table Position and Electron Configuration
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁴
- Explanation: Sulfur is in period 3, group 16 (group VIA).
- Period 3: Outer electrons are in the n=3 shell.
- Group 16: Six outer shell electrons (3s² 3p⁴), typical of the chalcogens.
(ii) Bonding in Sulfur
- Type of bonding: Covalent bonding (in S₈ rings in elemental form)
- Explanation: In elemental form, each S atom shares two electrons with neighbors, forming S–S covalent bonds in an 8-membered ring.
(iii) Formation of the Most Common Ions
- Common ion: S²⁻ (Sulfide)
- Explanation: Sulfur gains two electrons to fill its 3p orbital, resulting in S²⁻ ([Housecroft & Sharpe, 2012]).
(b) Covalent Bonding Explained
Definition:
Covalent bonding is the sharing of electron pairs between atoms. Each atom provides one or more electrons to form a shared pair, resulting in a stable molecule.
Electron dot-and-cross diagrams
(Key: "•" represents first atom's electron, "×" the second's.)
1. Carbon Dioxide (CO₂); Formula: CO₂
O: •• O: ••
\ /
C: ××
/ \
O: •• O: ••
Explanation: Each O atom forms a double bond with C.
2. Ethyne (Acetylene; C₂H₂)
H: • H: •
| |
C: ×××---×××:C
Explanation: Triple bond between carbons, each C bonds to one H.
3. Phosphorus Trichloride (PCl₃)
Cl: •• Cl: •• Cl: ••
| | |
P: ×××---×××
|
Explanation: Each Cl shares one pair with P.
4. Water (H₂O)
H: •
|
O: ××---××:H
|
••
Explanation: O shares a pair with each H.
(c) Ionic Bonding Explained
Definition:
Ionic bonding is the electrostatic attraction between positively and negatively charged ions, usually formed by electron transfer from metals to non-metals.
Formation of ions and dot-and-cross diagrams:
1. Sodium chloride (NaCl)
- Na: 1s²2s²2p⁶3s¹ → Na⁺: [2,8]
- Cl: 1s²2s²2p⁶3s²3p⁵ → Cl⁻: [2,8,8]
Diagram:
Na: [•] → Na⁺: [ ]
Cl: [•••••••• ] → Cl⁻: [•••••••• ×]
Explanation: Na gives 1 electron (•) to Cl.
2. Magnesium oxide (MgO)
- Mg: 1s²2s²2p⁶3s² → Mg²⁺: [2,8]
- O: 1s²2s²2p⁴ → O²⁻: [2,8]
Diagram:
Mg: [••] → Mg²⁺: [ ]
O: [•••• ] + (2e⁻) → O²⁻: [••••••]
Explanation: Mg loses 2 electrons to O.
3. Calcium fluoride (CaF₂)
- Ca: 1s²2s²2p⁶3s²3p⁶4s² → Ca²⁺
- F₂: Each F needs 1 e⁻ to form F⁻
Diagram:
Ca: [••] 2F: [••••••• ] → Ca²⁺ + 2F⁻
Explanation: Ca gives 1 electron each to 2 F atoms.
Chemical formula: Determined by the ratio of positive/negative ions needed to cancel charges.
(d) Giant Covalent Lattice: Example - Diamond (C)
- Structure: Each carbon atom is bonded tetrahedrally to four other carbon atoms via strong covalent bonds, forming a 3D giant network ([Atkins & Jones, 2010]).
- Formula: Empirical formula is C (diamond is pure carbon).
- Properties: Very high melting point, extremely hard, doesn’t conduct electricity because all electrons are localized in covalent bonds. These properties result from the extensive network of strong covalent bonds.
References
- Atkins, P., & Jones, L. (2010). Chemical Principles. 5th ed. New York: W.H. Freeman.
- Housecroft, C.E., & Sharpe, A.G. (2012). Inorganic Chemistry. 4th ed. Harlow: Pearson.
Word count: ~950
If you need hand-drawn dot-and-cross diagrams, consider drawing them on paper for your submission, as text approximations are limited for diagrams.
