设椭圆\(\dfrac{{x}^{2}}{{a}^{2}}+ \dfrac{{y}^{2}}{{b}^{2}}=1\left(a > b > 0\right) \) 的右顶点为\(A\),上顶点为\(B.\)已知椭圆的离心率为\(\dfrac{ \sqrt{5}}{3} \),\(\left|AB\right|= \sqrt{13} \).
\((I)\)求椭圆的方程;
\((II)\)设直线\(l:y=kx\left(k < 0\right) \)与椭圆交于\(P\),\(Q\)两点,
与直线\(AB\)交于点\(M\),且点\(P\),\(M\)均在第四象限\(.\)若\(∆BPM \)的面积是\(∆BPQ \)面积的\(2\)倍,求\(k\)的值.