The energy required to excite one Na atom 3.37 x 10⁻¹⁹J E = hc/λ where h = plancks constant = 6.626 x 10⁻³⁴J·s and λ = 589 nm = 589 x 10⁻⁹m and c = 3 x 10⁸ m/s E = (6.626 x 10⁻³⁴ x 3 x 10⁸) / 589 x 10⁻⁹m E = 3.37 x 10⁻¹⁹J Energy to excite one mole of na atom = (6.022 x 10²³) x 3.37 x 10⁻¹⁹ = 203kj
