Question

Quis critérios foram usadps por dobereiner em sua tentava de organiza os elementos químicos?

Answer 1

Döbereiner grouped the known elements into triads (sets of three) so that

• The atomic mass of the middle element was approximately the average    of the other two

• The chemical properties of the middle element were between those of the other two

• The physical properties of the middle element were between those of the other two

One example of a triad is Li – Na – K.

(a) Atomic mass of Na = 23.0 u

       Average atomic mass of Li and K = (6.9 u + 39.1 u)/2 = 46.0 u/2 = 23.0 u

(b) Li reacts slowly with water. Na reacts rapidly. Potassium reacts violently.

(c) Melting point of Na = 371 °C.

       Average melting point of Li and K = (454 °C + 330 °C)/2 = 784 °C/2

       = 392 °C