Group 13 Elements: The Boron Family
Chapter Name : The P- Block Elements |
Sub Topic Code : 102_11_11_02_06 |
Topic Name : Group 13 Elements: The Boron Family |
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Sub Topic Name : Chemical Properties |
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Introduction
• Due to small size of boron, the sum of its first three ionization enthalpies is very high. • This prevents it to form +3 ions and forces it to form only covalent compounds. But as we go from B to Al, the sum of the first three ionisation enthalpies of Al decreases, and it is able to form Al3+ ions. • When going down the group, due to poor shielding effect of intervening d and f orbitals, the increased effective nuclear charge holds ns electrons tightly (responsible for inert pair effect) and thereby, do not let them take part in bonding. • As a result of this, only p-orbital electron may be involved in bonding. • In trivalent state, the number of electrons around the central atom will be only 6 in a molecule. • Such electron deficient molecules have tendency to accept a pair of electrons to achieve stable electronic configuration and thus, behave as Lewis acids. • The tendency to behave as Lewis acid decreases with the increase in the size down the group. • BCl3 easily accepts a lone pair of electrons from ammonia to form BCl3?NH3. • Boron is unreactive in crystalline form. • These elements react with halogens to form trihalides (except Tl I3).
Pre-Requisites:
Elements, periodic table, Group, chemical properties
Activity:
• Group 13 has aluminium, boron which are important industrial elements.
Real Life Question:
What is aluminium used for?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| P block elements | Have the last electron in the outermost p orbital. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Periodic table, aluminium foil | Look at Groups 13 in the periodic table. Aluminium foil is made since aluminium is malleable. |
Real life uses :
• Aluminium is a metal used to make utensils, aircraft parts. Etc. • Aluminium can be beaten down into sheets making aluminium foil.
Places to visit :
Chemistry lab, kitchen.
Practical examples around us
| Examples | Explainations |
|---|---|
| Aluminium foil | Aluminium belongs to the group 13 elements. It is a soft metal which is malleable. |
What you learn in Theory:
• Due to small size of boron, the sum of its first three ionization enthalpies is very high. • This prevents it to form +3 ions and forces it to form only covalent compounds. But as we go from B to Al, the sum of the first three ionisation enthalpies of Al decreases, and it is able to form Al3+ ions. • When going down the group, due to poor shielding effect of intervening d and f orbitals, the increased effective nuclear charge holds ns electrons tightly (responsible for inert pair effect) and thereby, do not let them take part in bonding. • As a result of this, only p-orbital electron may be involved in bonding. • In trivalent state, the number of electrons around the central atom will be only 6 in a molecule. • Such electron deficient molecules have tendency to accept a pair of electrons to achieve stable electronic configuration and thus, behave as Lewis acids. • The tendency to behave as Lewis acid decreases with the increase in the size down the group. • BCl3 easily accepts a lone pair of electrons from ammonia to form BCl3?NH3. • Boron is unreactive in crystalline form. • These elements react with halogens to form trihalides (except Tl I3).
What you learn in Practice:
• Group 13 has aluminium, boron which are important industrial elements.