H, Li, and Na are all in the same group, what is the difference between these three elements?
Answers
Answer:
Explanation:
Group 1A (or IA) of the periodic table are the alkali metals: hydrogen (H), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). These are (except for hydrogen) soft, shiny, low-melting, highly reactive metals, which tarnish when exposed to air. The name comes from the fact that when these metals or their oxides are dissolved in water, a basic (alkaline) solution results. Because the alkali metals are very reactive, they are seldom (if ever) found in their elemental form in nature, and are usually found as ionic compounds (except for hydrogen).
The alkali metals have only one valence electron in their highest-energy orbitals (ns1). In their respective periods, they are the largest elements and have the lowest ionization energies. The valence electron is easily lost, forming an ion with a 1+ charge.
The alkali metals are solids at room temperature (except for hydrogen), but have fairly low melting points: lithium melts at 181ºC, sodium at 98ºC, potassium at 63ºC, rubidium at 39ºC, and cesium at 28ºC. They are also relatively soft metals: sodium and potassium can be cut with a butter knife.
Salts of the Group 1A elements tend to be extremely soluble in water. Because the alkali metal ions are relatively large (compared to other ions from the same period), their charges densities are low, and they are easily separated from their anions and solvated by polar solvents like water.
The alkali metals (again, except for hydrogen) react vigorously with water, producing the metal hydroxide, hydrogen gas, and heat.
2M(s) + H2O(l) ® MOH(aq) + H2(g)
(Heat plus hydrogen in an oxygen atmosphere is, of course, a very dangerous combination!) The reaction becomes more vigorous as one moves from top to bottom in Group 1A: lithium sizzles fiercely in water, a small amount of sodium reacts even more vigorously, and even a small amount of potassium metal reacts violently and usually ignites the hydrogen gas; rubidium and cesium explode. This is a result of the fact that the size of the element increases as we move down the group: as the size of the metal increases, the valence electron is farther away from the nucleus, and is thus more easily removed (i.e., the ionization energy is lower).