Group VII elements - Halogens

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Information about Group VII elements - Halogens

Published on March 2, 2014

Author: Giiang



Group VII elements


WHAT ARE GROUP VII ELEMENTS? • They are called halogens.

PHYSICAL PROPERTIES • These elements are non-metals. • At room temperature (25°C), they exist as diatomic molecules: F2, Cl2, Br2, and I2. • Their atoms have seven electrons in the outer principal quantum shell.


ATOMIC RADIUS Atomic Radius 0.14 0.12 0.1 0.08 Atomic Radius 0.06 0.04 0.02 0 Fluorine Chlorine Bromine Iodine

WHY? • Causeeee… • The number of layers of electrons around the nucleus. • The more layers, the bigger the atomic radius.

MELTING AND BOILING POINTS 250 200 150 100 50 Melting point 0 -50 -100 -150 -200 -250 Fluorine Chlorine Bromine Iodine Boiling point

MELTING AND BOILING POINTS • The boiling points show us the volatility (how easy can they evaporate) of the halogens. • They are relatively low cause they have simple molecular structure and weak van der Waals’ forces between their diatomic molecules. • These forces increase as the no. of electrons increase with increasing atomic number (the greater number no. of electrons, the greater the opportunities for dipoles arising within molecules). • => the larger the molecules, the stronger the van der Waals’ forces.

COLOUR Fluorine Pale yellow Chlorine Green/ Yellow

COLOUR Bromine Iodine Orange/ Brown Grey/ Black

REACTIONS • The halogen atoms require just one more electron to achieve a complete outer shell => they can react with metallic elements by gaining an electron to become ions with a 1- charge. • For example: • Cl2(g) + Ca(s)  CaCl2(s) • Each halogen atom tends to gain one electron • => halogens are oxidising agents, their oxidation no. is reduced from 0 to -1 in the compound formed.

REACTIONS • They also react with non-metals, forming covalent bonds. • For example: • H2(g) + Cl2(g)  2HCl(g) • The halogens get less reactive going down Group VII. This correspond to the trend in electronegativity going down the group. • Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. •

ELECTRONEGATIVITY Electronegativity 4.5 4 3.5 3 2.5 2 Electronegativity 1.5 1 0.5 0 Fluorine Chlorine Bromine Iodine

WHY? • Causeeeee… • The electrons are not as near to the nucleus as the number of electrons increase. Therefore, the nucleus and the electrons are not as attracted to each other as much. An increase in shielding is observed so the ability to attract electrons decrease. Which means electronegativity decrease down the group.

DISPLACEMENT REACTIONS • A more reactive halogen can displace a less reactive halogen from a halide solution of the less reactive halogen. • For example: • Cl2(aq) + 2NaBr(aq)  2NaCl(aq) + Br2(aq) • Ionic equation: • Cl2(aq) + 2Brˉ(aq)  2Clˉ(aq) + Br2(aq) • Halogens dissolve well in cyclohexane.


REACTION WITH HYDROGEN • Halogens form hydrogen halides with hydrogen gas. Equation for reaction Description of reaction H2(g) + F2(g)  2HF(g) Reacts explosively even in cool, dark conditions H2(g) + Cl2(g)  2HCl(g) Reacts explosively in sunlight H2(g) + Br2(g)  2HBr(g) Reacts slowly on heating H2(g) + I2(g)  2HI(g) Forms an equilibrium mixture on heating

WHYYYY? T_T • Because e e e e e. . . . . .. . . Hydrogen-halogen bond Bond energy / kJ/mol H-F 562 H-Cl 431 H-Br 366 H-I 299 • => HF is most thermally stable; HI is the least thermally stable.


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