Group VII Properties
Section: 8. The Periodic Table | Syllabus: Cambridge AS Level Physics 9702
The Halogens Group VII elements are called the halogens and include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are highly reactive non-metals that exist as diatomic molecules.
Halogens The elements in Group VII (or Group 17) of the Periodic Table, characterized by having seven electrons in their outer shell and forming salts when reacting with metals. Group VII Elements Element Symbol Atomic Number Electron Configuration Molecular Formula Fluorine F 9 2,7 F₂ Chlorine Cl 17 2,8,7 Cl₂ Bromine Br 35 2,8,18,7 Br₂ Iodine I 53 2,8,18,18,7 I₂ Word Origin The word "halogen" comes from Greek words meaning "salt-former" because halogens react with metals to form salts (like sodium chloride - table salt).
Common Features All halogens have seven electrons in their outer shell Exist as diatomic molecules (X₂) in their elemental form Need to gain one electron to achieve a stable noble gas configuration Form 1- ions (anions) by gaining one electron Very reactive non-metals Physical Properties Halogens show a clear trend in physical properties as you move down the group.
State at Room Temperature and Color Halogen State (at 25°C) Color Appearance Fluorine (F₂) Gas Pale yellow Pale yellow gas Chlorine (Cl₂) Gas Yellow-green Yellow-green gas Bromine (Br₂) Liquid Red-brown Red-brown volatile liquid Iodine (I₂) Solid Purple-black Dark grey/purple-black crystals States change from gas → liquid → solid down the group All halogens are colored Color deepens down the group Bromine is the only liquid non-metal at room temperature Iodine sublimes (solid → gas) when heated gently Melting and Boiling Points Halogen Melting Point (°C) Boiling Point (°C) Fluorine -220 -188 Chlorine -101 -34 Bromine -7 59 Iodine 114 184 Melting and boiling points increase down the group Larger molecules have stronger van der Waals forces More energy needed to overcome intermolecular forces Why Do Boiling Points Increase?
As molecules get larger down the group, they have more electrons. This creates stronger temporary dipoles and stronger van der Waals forces between molecules, requiring more energy to separate them. Volatility and Odor All halogens are toxic and have strong, unpleasant odors Volatility decreases down the group Chlorine: pungent, choking smell (used as poison gas in WWI) Bromine: strong, irritating smell, produces brown vapor Iodine: less volatile, produces purple vapor when heated Diagram Test tubes showing chlorine (yellow-green gas), bromine (red-brown liquid with vapor), and iodine (purple-black crystals with purple vapor) Chemical Properties Halogens are highly reactive non-metals that react by gaining electrons.
General Reactivity Very reactive non-metals - among the most reactive in the Periodic Table React by gaining one electron to form 1- ions Reactivity decreases down the group (F > Cl > Br > I) Form ionic compounds with metals Form covalent compounds with non-metals Powerful oxidizing agents (accept electrons) Why Does Reactivity Decrease Down the Group?
The atomic radius increases, so the outer shell is further from the nucleus. Nuclear attraction is weaker and there's more shielding, making it harder to attract and gain an electron. Ion Formation All halogens form 1- ions by gaining one electron: F + e⁻ → F⁻ (fluoride ion) Cl + e⁻ → Cl⁻ (chloride ion) Br + e⁻ → Br⁻ (bromide ion) I + e⁻ → I⁻ (iodide ion) These ions have a stable noble gas configuration Reactivity Order Most reactive: Fluorine > Chlorine > Bromine > Iodine :Least reactive Fluorine is the most reactive non-metal in the Periodic Table Can even react with gold and platinum Iodine is the least reactive halogen (still quite reactive) Reactions with Metals Halogens react with metals to form metal halides (ionic compounds also known as salts).
General Reaction General equation: Metal + Halogen → Metal Halide Reaction with Iron Iron + chlorine: 2Fe(s) + 3Cl₂(g) → 2FeCl₃(s) Heated iron wool glows brightly in chlorine gas Forms brown iron(III) chloride Very vigorous reaction Iron + bromine: 2Fe(s) + 3Br₂(l) → 2FeBr₃(s) Less vigorous than with chlorine Forms brown iron(III) bromide Iron + iodine: Fe(s) + I₂(s) → FeI₂(s) Least vigorous reaction Requires heating Forms grey iron(II) iodide (not iron(III)) Reaction with Sodium Sodium + chlorine: 2Na(s) + Cl₂(g) → 2NaCl(s) Burns with bright yellow flame Forms white sodium chloride (table salt) Highly exothermic reaction Halogen Vigor with Metals Example Product Fluorine Extremely vigorous NaF (sodium fluoride) Chlorine Very vigorous NaCl (sodium chloride) Bromine Moderately vigorous NaBr (sodium bromide) Iodine Least vigorous NaI (sodium iodide) Safety Warning Halogens are toxic and corrosive.
Fluorine and chlorine are especially dangerous gases. Always use proper ventilation and protective equipment when handling halogens. Diagram Iron wool burning in chlorine gas with bright glow, forming brown iron(III) chloride Reactions with Hydrogen Halogens react with hydrogen gas to form hydrogen …
Interactive revision notes, videos and practice questions load below.