Chemistry- 4.3: Formation of Ionic Compounds notes/ Questions

Explain why Potassium Chloride has the formula KCl, whereas the formula of Calcium Chloride is CaCl2

Because an atom of K has one more electron than an atom of a noble gas and an atom of Cl has one less, in a reaction one K atom can donate one electron to one Cl atom to give K+ and Cl-, both of which have the electronic configuration of the noble gas argon. The formula of this compound is, therefore, KCl. A Ca atom will lose two electrons to gain a noble gas configuration. Because each Cl atom will gain only one electron, there will be two chlorine atoms for each Ca atom. This reaction will therefore produce Ca2+ ions and Cl- ions. The formula of the compound is, therefore, CaCl2

Why are group two metals of the periodic table likely to form cations with a 2+ charge?

Group 2 metals have two electrons in their valence shell. They lose these two electrons and therefore become positively charged, as they still have the original number of protons. Cations are ions with a positive charge

Explain why elements in group 17 of the periodic table are likely form ions with a -1 charge

They have seven electrons in their outer shell so only need to gain on electron to satisfy the octet rule. This means they become more negative by gaining one electron.

Write an equation for the reaction between the following metal and non-metal atoms. Show the electronic configurations for each element before and after the reaction. a) Sodium and Chlorine atoms b) Magnesium and Oxygen atoms c) Aluminium and Sulfur atoms

a) Na (2,8,1) + Cl (2,8,7) = Na+ (2,8) + Cl- (2,8,8) b) Mg (2,8,2) + O (2,6) = Mg2+ (2,8) + O2- (2,8) c) 2Al (2,8,3) + 3S (2,8,6) = 2Al3+ (2,8) + 3S2- (2,8,8)

Indicate whether the following atoms will form cations and anions and explain why. a) Calcium b) Nitrogen c) Fluorine d) Aluminium e) Phosphorus

a) cation b) anion c) anion d) cation e) anion Metals form cations and non-metals form anions. Metals have low electronegativities and so it is easier for metals to lose electrons than it is for non-metals.