![]() The following is a table of the flame colours observed in the group 1 and 2 elements: The reaction with oxygen to form a metal oxide occurs spontaneously in air and when the metals are heated by flame, showing a distinct colour.The heavier, less dense and less polarizing ions like Sr 2 and Ba 2 cannot do this, so the metal peroxide is stable. The peroxide ion becomes a stable O 2- oxide ion and the weak O-O covalent bond breaks. These are small with a very high charge density which draws the 2- negative charge in the peroxide ion towards it with great strength (they polarize the ion). ![]() It does not form in this reaction with the smaller group 2 metals such as Be or Mg because they form highly polarizing ions. The peroxide ion ( -O-O -) has two oxygen atoms, each with a weak covalent bond to the other, and a 1- charge (O 2 2- overall). In the reaction with heavier group two metals, a metal peroxide can form, such as with barium and strontium: This can be written generally as:Īgain, the stoichiometry is slightly different in the two reactions. Another common reaction is the group 1 or 2 reaction with oxygen.The stoichiometry is slightly different because two hydroxide groups will be bonded to the group 2 metal because it forms a 2 ion, unlike the 1 ion of a group 1 metal. The equation can be written generally as:ĢM (s) 2H 2O (l) \, → \, 2MOH (aq) H 2 (g) Group 1 and group 2 metals are both known for reacting vigorously with water compared to other metals. One of the most common reactions with group 1 and 2 elements is the reaction with water.The reactions of group 1 and group 2 metals are very similar because they have similar outer shell configurations and elements in both groups are prone to losing their outer shell electrons.Greater shielding makes losing the one (in group 1) or two (in group 2) outer shell electrons increasingly easy, and therefore reactivity in general increases going down the two groups. For example, both group 1 and group 2 show a decrease in ionization energies going down the group.Īs explained in Periodic Trends: Ionization Energy, this is due to greater shielding from more inner electron shells between the nucleus and the outer shell. As you descend the table, a similar trend in the change in properties is observed in both groups.In these compounds, you’ll see alkali metals with a 1 charge (such as in NaCl), whereas alkaline earth metals will hold a 2 charge (such as in MgCl 2). As they are metals, they form ionic compounds with non-metals. The alkali metals all have a valence of 1 and alkaline earth metals have a valence of 2.Ionization energies of the elements decrease.The melting point of the metals gets lower.As you go down the group, the properties of the elements change in the following ways:.The products of this reaction are hydrogen gas and a metal hydroxide – this forms an alkaline solution, which gives the two groups their names.They are reactive, more so than d-block metals in general and they react vigorously with water. ![]() They have relatively low melting points compared to metals in general.They are relatively low density metals.Alkali metals and alkaline earth metals have the following properties:.Because of their reactivity, they were not isolated as metals until later on. Their oxides all produce alkaline solutions in water, which is how they get their names. They have been known for quite a long time through their compounds, like their metal oxides, because they are reactive and quickly form compounds with oxygen in air. The alkali metals in group 1 and the alkaline earth metals in group 2 are very well-studied groups of elements, with clear patterns in how their properties change.Their behaviour in chemical reactions is similar because of the similar outer shell configuration. Groups 1 and 2 have 1 and 2 electrons in the outer shell, respectively. Therefore, it is easy to see which elements have similar properties to each other – they will be in the same column of the table as each other, the columns which we call groups. The number of outer shell electrons dictates the chemical properties of an element. We saw earlier that the Periodic Table is arranged, left to right, by proton number and number of outer shell electrons.To know the common reactions of group 1 and group 2 elements.To apply knowledge of electronic structure and bonding to explain the trends in group 1 properties. ![]()
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