(credit a: modification of work by Serge Lachinov credit b: modification of work by “Den fjättrade ankan”/Wikimedia Commons)īy the twentieth century, it became apparent that the periodic relationship involved atomic numbers rather than atomic masses. (a) Dimitri Mendeleev is widely credited with creating (b) the first periodic table of the elements. Although Mendeleev and Meyer had a long dispute over priority, Mendeleev’s contributions to the development of the periodic table are now more widely recognized ( Figure 1).įigure 1.
The discoveries of gallium (1875) and germanium (1886) provided great support for Mendeleev’s work. But Mendeleev went one step further than Meyer: He used his table to predict the existence of elements that would have the properties similar to aluminum and silicon, but were yet unknown. Both published tables with the elements arranged according to increasing atomic mass. Fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) also exhibit similar properties to each other, but these properties are drastically different from those of any of the elements above.ĭimitri Mendeleev in Russia (1869) and Lothar Meyer in Germany (1870) independently recognized that there was a periodic relationship among the properties of the elements known at that time. For example: Li, Na, and K are much more reactive than are Ca, Sr, and Ba Li, Na, and K form compounds with oxygen in a ratio of two of their atoms to one oxygen atom, whereas Ca, Sr, and Ba form compounds with one of their atoms to one oxygen atom. However, the specific properties of these two groupings are notably different from each other. A second grouping includes calcium (Ca), strontium (Sr), and barium (Ba), which also are shiny, good conductors of heat and electricity, and have chemical properties in common. One such grouping includes lithium (Li), sodium (Na), and potassium (K): These elements all are shiny, conduct heat and electricity well, and have similar chemical properties. Identify metals, nonmetals, and metalloids by their properties and/or location on the periodic tableĪs early chemists worked to purify ores and discovered more elements, they realized that various elements could be grouped together by their similar chemical behaviors.Predict the general properties of elements based on their location within the periodic table.State the periodic law and explain the organization of elements in the periodic table.If damp blue litmus paper is used, the paper turns red then white.By the end of this section, you will be able to: 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.
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