Group 17 <3

• Halogens are Group 17 elements and they are non-metals
• All halogen atoms have 7 valence electrons
• Halogens exist as diatomic molecules at room temperature
• There are single bonds between the two atoms in each halogen molecule
• The colour of each halogen element gets darker as you go down the group
• The melting and boiling points of halogens increase going down the group because the atomic size increases, leading to more electrons and stronger intermolecular forces that require more energy to break
• Volatility is a measure of how easily a substance evaporates
• All halogens have low melting and boiling points due to weak van der Waal’s forces between their diatomic molecules, caused by instantaneous induced dipole-dipole forces
• The larger the halogen molecule, the stronger the van der Waal’s forces between the molecules
• Iodine is the least volatile halogen and fluorine is the most volatile
• Halogens need to gain just one electron to achieve a stable electron configuration
• Reactivity of halogens decreases down the group
• Cl2 --> 2Cl- + 2e- (chlorine gains 2 electrons to form chloride ions)
• Oxidising agents accept electrons
• Electronegativity is a measure of how strongly an atom attracts electrons in a chemical bond
• Electronegativity decreases down Group 17
• Electronegativity decreases down the group because the atomic size increases, leading to decreased attraction between electrons and nucleus
• Fluorine is the most reactive halogen due to its small atomic radii and least shielding in Group 17, making it a strong oxidising agent compared to iodine
• Factors of reactivity:

  - number of valence electrons, fewer valence electrons = higher reactivity

  - atomic size, smaller atoms = higher reactivity

  - electronegativity, higher electronegativity = high reactivity
• Halides are compounds formed by the combination of halogen elements with other elements
• Halogens that are more reactive can displace a less reactive halogen from a halide solution
• Displacement reactions demonstrate that the oxidising power of the halogens decreases going down group 17
• Cyclohexane is a colourless liquid that is immiscible in water and forms a layer on top of water
• Immiscible means that two liquids do not dissolve in each other and form separate layers
• Reaction of fluoride with hydrogen:

  • Reacts explosively even in cool and dark conditions
• Reaction of chlorine with hydrogen:

  • Reacts explosively in sunlight
• Reaction of bromine with hydrogen:

  • Reacts slowly on heating
• Reaction of iodine with hydrogen:

  • Forms an equilibrium mixture on heating