Known as halogens, the Group 17 is a family of nonmetals which have a high reactivity. These elements react with metals and other nonmetals to produce salts and halides. They are also used in various industrial and medical applications. The group 17 elements are located on the second column of the right side of the periodic table. Their atoms are one electron away from achieving a stable noble gas structure. Group 17 includes Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At) and Tennessine (Ts). All group 17 elements have seven electrons in the outermost shell of the atom. The last electron in these elements is placed in the p-orbital. The number of quantum shells increases as the group moves down the table. These elements all have a -1 oxidation state and all have seven electrons in the outermost shell (Varshni, 2007).
1. Electronic configuration of Group 17 elements
General electronic configuration of group 17 is ns2 np5 while the electronic configuration of Group 17 members is as follows (Peterson & Yousaf, 2010).
F [9] 1s2 2s2 2p5 or [He] 2s2 2p5
Cl [17] 1s2 2s2 2p6 3s2 3p5 or [Ne] 3s2 3p5
Br [35] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 or [Ar] 3d10 4s2 4p5
I [53] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5 or [Kr] 5s2 4d10 5p5
At [85] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p5 or [Xe] 6s2 4f14 5d10 6p5
Ts [117] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 or [Rn] 7s2 5f14 6d10 7p5
2. Anomalous behavior of Fluorine
• Among the members of the halogen family, fluorine exhibits the most anomalous behavior. The chemistry of this element varies from being a gas at room temperature to a liquid at the other end of the spectrum. The anomalous properties of fluorine have not only prompted scientists to explore its chemistry, but they have also caused students to question the true nature of the halogens.
• Aside from its anomalous properties, fluorine also has some of the highest electronegativity values amongst the halogens. Fluorine is also the smallest of the halogens, having an atomic diameter of just ten millimeters. In fact, its smallest atomic size makes it the smallest atom in the halogen family, but despite its diminutive size, fluorine is the most reactive halogen of all.
• One of the more intriguing properties of fluorine is its anomalous boiling point. This can be explained by its higher electronegativity value and the fact that fluorine is less polarizable than its more polarized cousins. The halogens also have a positive oxidation state, which means that they are prone to forming hydrogen bonds. These bonds can lead to interesting properties, like fluorine forming an electron cloud .Compared to its fellow halogens, fluorine has the highest reducing power and the highest electron gain enthalpy.
3. Trend in the physical properties of Group 17 Elements
They have low boiling and melting points. The bond strength between halogens and hydrogen decreases as the group moves down the periodic table (Lo, et al., 2015). As the group goes down, the atom size increases, while the effective nuclear charge decreases. This leads to more shielding of the valence shell electrons. As a result, halogens tend to share electrons to get their ideal gaseous configuration.
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3.1. Atomic and ionic radii of Group 17 Elements
Atomic and ionic radii of group 17 elements increases from fluorine to astatine while radius of Ts is unknown.
Figure 1: Atomic radius of Group 17 elements
Figure 2: Ionic radius of Group 17 elements
3.2. Ionization energy of Group 17 Elements
Ionization energy of group 16 elements decrease from Fluorine to Tennessine.
Ionization energy of group 16 elements in kilo joule per mole
Figure 3: First Ionization Energy of the Group 17 elements
3.3. Electronegativity of Group 17 Elements
Electronegativity of group 17 elements decrease from fluorine to Astatine while this value is unknown for Tennessine.
F 4
Cl 3
Br 2.8
I 2.5
At 2.1
3.4. Melting and boiling point of Group 17 Elements
Melting and boiling point of this group elements increases from top to bottom.
Figure 4: Melting and Boiling Points of the Group 17 elements
4. Chemical properties of Group 17 Elements
Halogens are very reactive nonmetals that are found in the earth’s crust as halide ions. They are strong, nonmetals that are used for chemical reaction. Their chemical properties are determined by their oxidation states and reaction with metals. Chemical properties are weaker than those of other groups. They have an oxidation strength of -1. They are considered to be salt-formers and act as oxidizing agents in displacement reactions. When halogens are exposed to metals, they react with the metal to produce salts. They are also reactive with water. When they react with water, they form a blue litmus paper. This indicates that the solution is acidic (Peterson & Yousaf, 2010; Lo, et al., 2015)
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4.1. Oxidizing power
• Among the group 17 elements, fluorine and chlorine are the strongest oxidizers. The oxidizing power of these elements depends on their hydration enthalpy and electronegativity values.
• Iodine is also an oxidizing agent. When it combines with hydrogen, it forms acidic hydrogen halides. It also acts as a bactericide. It has a high electron affinity and oxidizes silicon. However, it is not as soluble in water as fluorine.
• Iodine has an oxidation state of +7. However, its bond dissociation energy is lower than that of chlorine. This means that it will seek to make a ionic bond with other elements in order to get an electron back.
• Bromine is a halogen that can oxidize iodine. Bromine has a lower electron affinity than fluorine. It has a bond enthalpy of half the enthalpy of chlorine. It is also the only radioactive element in the group.
4.2. Reaction with oxygen
Group 17 elements reacts with oxygen and form oxides.
Scheme 1: Reaction of Group 17 elements with oxygen
4.3. Reaction with hydrogen
Halogens reacts with hydrogen and form corresponding hydrides.
Scheme 2: Reaction of Group 17 elements with hydrogen
4.4. Reaction with metals
Halogens reacts with metals and form corresponding ionic halides.
Scheme 3: Reaction of Group 17 elements with metals
Conclusion
Known as the halogens, group 17 is a group of non-metallic, reactive and poisonous elements. It comprises of Fluorine, Bromine, Iodine and Astatine. They form salts when they combine with metals. They also react with hydrogen to form hydrogen halides. Among the elements of the periodic table, Group 17 is one of the most important. The members of this group share one electron to form a covalent bond. When combined with other elements, they form compounds that are in an odd oxidation state.
References
1. Lo, S. H., Kwan, A. K. H., Ouyang, Y., & Ho, J. C. M. (2015). Finite element analysis of axially loaded FRP-confined rectangular concrete columns. Engineering Structures, 100, 253-263.
2. Peterson, K. A., & Yousaf, K. E. (2010). Molecular core-valence correlation effects involving the post-d elements Ga–Rn: Benchmarks and new pseudopotential-based correlation consistent basis sets. The Journal of chemical physics, 133(17), 174116.
3. Varshni, Y. P. (2007). Critical temperatures of elements from their boiling points. Physics and Chemistry of Liquids, 45(6), 601-607.