Q.Considering the atomic number and position in the periodic table, arrange the following elements in the increasing order of metallic character: Si, Be, Mg, Na, P.
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Start your 14-day free trial to unlock the full solution →Metallic character increases down a group and decreases across a period. Using periodic trends, the increasing order of metallic character is: P < Si < Be < Mg < Na.
Why Metallic Character Follows This Trend
Metallic character describes how easily an atom loses its outermost electrons to form positive ions. The easier it is to lose electrons, the more metallic the element.
Two factors control this:
- Ionisation enthalpy — the energy needed to remove an electron. Lower ionisation enthalpy means higher metallic character.
- Atomic size — larger atoms hold their outermost electrons more loosely because the nucleus is farther away and there is more shielding by inner electrons.
So metallic character increases when atoms get larger (down a group) and decreases when atoms get smaller (across a period). This is the exact opposite of the trend for ionisation enthalpy.
A common mistake is to confuse metallic character with non-metallic character. Remember: metallic character increases down a group (like Na being more metallic than Li) and decreases across a period (like Na being more metallic than Mg). Non-metallic character follows the reverse trend.
Step-by-Step Reasoning
1. Identify the positions of all five elements in the periodic table.
| Element | Group | Period |
|---|---|---|
| Be | 2 | 2 |
| Mg | 2 | 3 |
| Na | 1 | 3 |
| Si | 14 | 3 |
| P | 15 | 3 |
Four of these elements (Mg, Na, Si, P) lie in the third period. Only Be is in the second period.
2. Compare elements within the same period (Period 3).
Across Period 3, from left to right: Na → Mg → Si → P.
Metallic character decreases sharply across a period. Why? Because nuclear charge increases while electrons are added to the same shell. The nucleus pulls the electron cloud tighter, making it harder to lose electrons.
- Na (Group 1) — has only one valence electron, very loosely held. Highly metallic.
- Mg (Group 2) — has two valence electrons, held a bit more tightly. Still metallic, but less than Na.
- Si (Group 14) — a metalloid. It has four valence electrons and a much higher ionisation enthalpy. Weakly metallic.
- P (Group 15) — a non-metal. Five valence electrons, high ionisation enthalpy. Least metallic in this set.
So within Period 3 alone: P < Si < Mg < Na (increasing metallic character). …
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