What is the trend of melting and boiling point of the elements of short periods as we move from left to right in a periodic table?
Correct answer: C. Melting and boiling points first increase then decrease
- A. Melting and boiling points first decrease then increase
- B. Melting and boiling points increase gradually
- C. Melting and boiling points first increase then decrease
- D. Melting and boiling points decrease gradually
Explanation
In general, the melting point increases across a period up to group 14 and then decreases from group 14 to group 18.From sodium to aluminum there is metallic bonding, the strength of metallic bonding increases across the period due to an increase in ionic charge (so greater electrostatic attraction) and larger nuclear charge (positively charged nucleus is closer to delocalized electrons so less shielding). Hence, melting/boiling points generally increase.From phosphorus to argon the atoms form simple covalent structures in which the strength of intermolecular forces determines the melting/boiling points. Vanderwaal's forces increase with more electrons and larger molecules. (Silicon however has a giant covalent structure, much stronger bonds, and therefore a high melting/boiling point).
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About Periodic Properties and Trends
Periodic properties arise from electron configuration and effective nuclear charge, producing trends in atomic and ionic radius, ionization energy, electron affinity, electronegativity, metallic character and reactivity. Comparisons run across periods and down groups, with attention to common exceptions. The topic also relates these trends to the behavior of s-block and p-block elements.
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