Elemental cesium reacts more violently with water than does elemental sodium.

Upon reacting with water, elemental Cesium reacts more violently than elemental Sodium (True). 

Sodium would float on the water surface to react quickly with water, giving off heat and forming hydrogen gas and sodium hydroxide solids which quickly dissolve in water to form a sodium hydroxide solution. In contrast, cesium would explode upon contact with water. 

All the group 1 (alkali metal) elements in the periodic table generally have high reactivity including with water. This trend can be attributed to several factors such as the ionization and the atomization energy of the elements. Ionization energy is the energy needed to remove the most loosely bound electron to form a cation (positively-charged ion). Atomization energy reflects the strength of the metallic bonds of the elements as it is the energy required for one mole of the element into atoms.

Going down Group 1 elements in the periodic table (from top to bottom: lithium, sodium, potassium, rubidium, cesium), the ionization and the atomization energy both decrease, making it easier to form the cations and to dissociate the metallic bonds. As a result, the energy needed for the reaction to proceed decreases, in turn, increasing the reactivity of the elements.