The transition elements and inner transition elements also do not follow the octet rule: Because hydrogen only needs two electrons to fill its valence shell, it is an exception to the octet rule. These four electrons can be gained by forming four covalent bonds, as illustrated here for carbon in CCl 4 (carbon tetrachloride) and silicon in SiH 4 (silane). For example, each atom of a group 14 element has four electrons in its outermost shell and therefore requires four more electrons to reach an octet. The number of bonds that an atom can form can often be predicted from the number of electrons needed to reach an octet (eight valence electrons) this is especially true of the nonmetals of the second period of the periodic table (C, N, O, and F). The tendency of main group atoms to form enough bonds to obtain eight valence electrons is known as the octet rule. This allows each halogen atom to have a noble gas electron configuration. If damp blue litmus paper is used, the paper turns red then white.The other halogen molecules (F 2, Br 2, I 2, and At 2) form bonds like those in the chlorine molecule: one single bond between atoms and three lone pairs of electrons per atom. Chemical test for chlorineĭamp litmus paper is bleached white when it is placed in chlorine. A little hydrogen astatide should form, which should dissolve in water to form an acidic solution.
Use the information to predict the reaction of astatine with hydrogen.Īstatine should react very slowly with hydrogen, even when heated. Very slow reaction when heated strongly, forming some hydrogen iodideĪstatine is placed below iodine in group 7. Vigorous reaction with burning hydrogen, forming hydrogen bromide HalogenĮxplodes in the cold and dark, forming hydrogen fluorideĮxplodes with a flame or in sunlight, forming hydrogen chloride The table describes what is seen when halogens react with hydrogen. Hydrogen chloride dissolves in water to produce hydrochloric acid, HCl(aq). They dissolve in water to produce acidic solutions. The hydrogen halides are gases at room temperature. For example, chlorine reacts with hydrogen: The halogens react with hydrogen to produce compounds called hydrogen halides. Reveal answerĢFe(s) + 3Cl 2 (g) → 2FeCl 3 (s) Reactions with hydrogen Write a balanced equation for the reaction of iron with chlorine to produce solid iron(III) chloride,įeCl 3. Hot iron wool reacts slowly in iodine vapour to produce grey iron(II) iodide Hot iron wool burns quickly to produce red-brown iron(III) bromide Hot iron wool burns vigorously to produce orange-brown iron(III) chloride HalogenĬold iron wool burns to produce white iron(III) fluoride The table describes what is seen when halogens react with iron wool. The halogens become less reactive going down group 7. Sodium and chlorine react vigorously when heated, giving an orange flame and clouds of white For example, chlorine reacts with sodium: The halogens react with metals to produce salts (the word 'halogen' means 'salt former'). This means that the halogens all have similar chemical properties. Atoms of group 7 elements all have seven electrons in their outer shell.