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GROUP 17 p-BLOCK. PART-1 with audio.pptx

Group 17 elements, known as halogens, include fluorine, chlorine, bromine, iodine, astatine, and tennessine, characterized by their high reactivity and salt-producing nature. They exhibit unique trends in atomic size, ionization enthalpy, electron gain enthalpy, and electronegativity, with fluorine being the most electronegative and the strongest oxidizing agent among them. Physical properties vary, including states of matter and color, with increasing melting and boiling points down the group.

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Periodic Table Overview•
Group 17 Elizabeth Abraham Mani
Introduction The elements in group 17 are collectively referred to as the “halogens,” which means “salt producing.” The valence shell electronic configuration of these elements is ns2 np 5. Owing to their high reactivity, the halogens do not occur in free state, but in combined state in nature.
Members of Group 17 Fluorine (F) [He]2s2,2p5 Chlorine (Cl) [Ne]3s2,3p5 Bromine (Br) [Ar]3d104s24p5 Iodine (I) [Kr]4d10,5s2,5p5 Astatine (At) [Xe]4f14,5d10,6s2,6p5 Tennessine (Ts) [Rn] 5f14, 6d10, 7s2, 7p5
• Fluorine occurs widely as insoluble fluorides: (fluorspar CaF2, cryolite,Na3AlF6 and fluoroapatite 3Ca3 (PO4)2.CaF2) • Chlorine, bromine and iodine are present in sea water in the form of chlorides, bromides and iodides. • The principal source of iodine is sea weeds for example, contain upto 0.5% of iodine and Chile saltpetre contains up to 0.2% of sodium iodate. • Astatine and Tennessine are radioactive elements.
Atomic Size • The halogens have the smallest atomic radii in their respective periods due to maximum effective nuclear charge. • Atomic size increases down the group due to addition of new shells as we move down the group.
Ionisation Enthalpy • They have little tendency to lose electron. Thus they have very high ionisation enthalpy. • Due to increase in atomic size, ionisation enthalpy decreases down the group.
Electron Gain Enthalpy Halogens have maximum negative electron gain enthalpy in the corresponding periods. • This is due to the fact that Halogens have the smallest size in their respective periods and therefore high effective nuclear charge and thus they readily gain electron. • Also the atoms of these elements have only one electron less than stable noble gas configurations (ns2 np5). As a consequence, they readily accept one electron to acquire noble gas electronic configuration. • Down the group, electron gain enthalpy becomes less negative.
The Electron Gain Enthalpy of fluorine is less negative than that of chlorine. Why? Fluorine (F) [He]2s2,2p5 Chlorine (Cl) [Ne]3s2,3p5 Due to small size of fluorine atom there are strong interelectronic repulsions in the relatively small 2p orbitals of fluorine and thus, the incoming electron does not experience much attraction.
Electronegativity • They have very high electronegativity. • The electronegativity decreases down the group. • Down the group electronegativity decreases as the size increases. • Fluorine is the most electronegative element in the periodic table.
Physical Properties • Physical State Fluorine and Chlorine → Gases Bromine → Liquid Iodine → Solid • Colour All halogens are coloured. This is due to absorption of radiations in visible region which results in the excitation of outer electrons to higher energy level. By absorbing different quanta of radiation, they display different colours. Fluorine: Dull Yellow in color. Chlorine: Greenish yellow. Bromine: Reddish brown. Iodine: Violet.
Physical Properties • Melting point and boiling points: It increases down the group .As size and mass increases the Vander wall force also increases, therefore melting and boiling point increases. • Solubility Fluorine and chlorine react with water. Bromine and iodine are only sparingly soluble in water but are soluble in various organic solvents such as chloroform, carbon tetrachloride, carbon disulphide and hydrocarbons to give coloured solutions
Anomalous Behavior of Fluorine Reasons: • Smallest size. • Highest electronegativity. • Low F-F bond dissociation energy. • No vacant d orbital
Examples for Anomalous Behaviour Of Fluorine • ΔegH of F2 is less negative than that of Cl2. • F-F bond dissociation enthalpy is less than that of Cl-Cl bond. • F2 exhibits only -1 oxidation state whereas other halogens can exhibit variable oxidation states like +1, +3, +5, or +7 • F2 forms only one oxoacid while other halogens form a number of oxoacids. Note: HF is a liquid whereas other Hydrogen halides are gases Hydrogen fluoride is a liquid (b.p. 293 K) due to strong hydrogen bonding. Hydrogen bond is formed in HF due to small size and high electronegativity of fluorine.
Bond dissociation enthalpy of F2 is smaller compared to that of Cl2. Why? Due to the small size of Fluorine atom, lone pairs on F2 are much closer to each other than in the case of Cl2. This results in large electron-electron repulsion among the lone pairs and hence F-F bond dissociation enthalpy is low. X-X bond dissociation enthalpies from chlorine onwards show the expected trend: Cl – Cl > Br – Br > I – I Thus decreasing order X-X bond dissociation enthalpy can be given as: Cl – Cl > Br – Br > F - F > I – I
Why fluorine is the strongest oxidising agent amongst the halogens? It is due to: • Low enthalpy of dissociation of F-F bond • High hydration enthalpy of F– ion. Note: Fluorine is the strong oxidizing agent among all Halogens
To be Continued…