Write the electron dot structure for calcium and oxygen. The atomic numbers of calcium and oxyzen are 20 and 8 respectively. Show the formation of calcium oxide by the transfer of electrons. Ionic compounds are high melting solids.
The Correct Answer and Explanation is:
Electron Dot Structure for Calcium and Oxygen
- Calcium (Ca) has an atomic number of 20, which means it has 20 electrons. The electron configuration of calcium is:
[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2
]
Calcium has two electrons in its outermost shell (4s²), which are available for bonding. In the electron dot structure, these two electrons are represented as dots around the element symbol:
[
\text{Ca: } \, \cdot \cdot
] - Oxygen (O) has an atomic number of 8, with the electron configuration:
[
1s^2 \, 2s^2 \, 2p^4
]
Oxygen has six electrons in its outermost shell (2s² 2p⁴), needing two more electrons to complete its octet. The electron dot structure for oxygen shows six dots around the symbol:
[
\text{O: } \, \cdot \cdot \, \cdot \cdot \, \cdot
]
Formation of Calcium Oxide (CaO)
Calcium oxide (CaO) is formed by the transfer of electrons between calcium (Ca) and oxygen (O) atoms.
- Calcium’s behavior:
- Calcium has two electrons in its outer shell, which it can lose to achieve a stable electron configuration similar to that of noble gases.
- When calcium loses these two electrons, it becomes a Ca²⁺ ion (with a +2 charge):
[
\text{Ca: } \, \cdot \cdot \rightarrow \text{Ca}^{2+} + 2e^-
]
- Oxygen’s behavior:
- Oxygen needs two electrons to complete its octet and become stable.
- Oxygen accepts the two electrons lost by calcium to form an O²⁻ ion (with a -2 charge):
[
\text{O: } \, \cdot \cdot \, \cdot \cdot \, \cdot \rightarrow \text{O}^{2-} + 2e^-
]
- Ionic Bond Formation:
- The calcium ion (Ca²⁺) and the oxide ion (O²⁻) are now oppositely charged. Since opposite charges attract, the two ions form an ionic bond to create calcium oxide (CaO):
[
\text{Ca}^{2+} + \text{O}^{2-} \rightarrow \text{CaO}
]
High Melting Point of Ionic Compounds
Ionic compounds, such as calcium oxide (CaO), are high-melting solids because the electrostatic forces between the positively charged calcium ions (Ca²⁺) and the negatively charged oxide ions (O²⁻) are very strong. These strong ionic bonds require a large amount of energy to break, leading to a high melting point. Calcium oxide, specifically, has a melting point of around 2,572°C, demonstrating the strength of its ionic bonds.