1.14: Other Periodic Properties of Atoms
- Page ID
- 443923
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Melting Point Trends
The melting points is the amount of energy required to break a bond(s) to change the solid phase of a substance to a liquid. Generally, the stronger the bond between the atoms of an element, the more energy required to break that bond. Because temperature is directly proportional to energy, a high bond dissociation energy correlates to a high temperature. Melting points are varied and do not generally form a distinguishable trend across the periodic table. However, certain conclusions can be drawn from Figure \(\PageIndex{7}\).
- Metals generally possess a high melting point.
- Most non-metals possess low melting points.
- The non-metal carbon possesses the highest melting point of all the elements. The semi-metal boron also possesses a high melting point.
Metallic Character Trends
The metallic character of an element can be defined as how readily an atom can lose an electron. From right to left across a period, metallic character increases because the attraction between valence electron and the nucleus is weaker, enabling an easier loss of electrons. Metallic character increases as you move down a group because the atomic size is increasing. When the atomic size increases, the outer shells are farther away. The principal quantum number increases and average electron density moves farther from nucleus. The electrons of the valence shell have less attraction to the nucleus and, as a result, can lose electrons more readily. This causes an increase in metallic character.
- Metallic characteristics decrease from left to right across a period. This is caused by the decrease in radius (caused by Zeff, as stated above) of the atom that allows the outer electrons to ionize more readily.
- Metallic characteristics increase down a group. Electron shielding causes the atomic radius to increase thus the outer electrons ionizes more readily than electrons in smaller atoms.
- Metallic character relates to the ability to lose electrons, and nonmetallic character relates to the ability to gain electrons.
Another easier way to remember the trend of metallic character is that moving left and down toward the bottom-left corner of the periodic table, metallic character increases toward Groups 1 and 2, or the alkali and alkaline earth metal groups. Likewise, moving up and to the right to the upper-right corner of the periodic table, metallic character decreases because you are passing by to the right side of the staircase, which indicate the nonmetals. These include the Group 8, the noble gases, and other common gases such as oxygen and nitrogen.
- In other words:
- Move left across period and down the group: increase metallic character (heading towards alkali and alkaline metals)
- Move right across period and up the group: decrease metallic character (heading towards nonmetals like noble gases)
Problems
Which has more metallic character, Lead (Pb) or Tin (Sn)?
- Answer
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Lead
Lead and tin share the same column. Metallic character increases down a column. Lead is under tin, so lead has more metallic character.
Which element has a higher melting point: chlorine (Cl) or bromine (Br)?
- Answer
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Bromine
In non-metals, melting point increases down a column. Because chlorine and bromine share the same column, bromine possesses the higher melting point.
Arrange these elements according to increasing metallic character: Li, S, Ag, Cs, Ge
- Answer
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Li, S, Ge, Ag, Cs