In a chromomagnetic model, we analyze the properties of the newly observed P c ð4457Þ þ , P c ð4440Þ þ , and P c ð4312Þ þ states. We estimate the masses of the ðuudÞ 8 c ðccÞ 8 c and ðudsÞ 8 c ðccÞ 8 c pentaquark states by considering the isospin breaking effects. Their values are determined by calculating mass distances from the Σ þþ c D − and Ξ 0þ c D − thresholds, respectively. It is found that the isospin breaking effects on the spectrum are small. From the uncertainty consideration and the rearrangement decay properties in a simple model, we find that it is possible to assign the P c ð4457Þ þ , P c ð4440Þ þ , and P c ð4312Þ þ as J P ¼ 3=2 − , 1=2 − , and 3=2 − pentaquark states, respectively. The assignment in the molecule picture can be different, in particular for the P c ð4312Þ þ . The information from open-charm channels, e.g., B½P c → Σ þþ c D − =B½P c → J=ψp, will play an important role in distinguishing the inner structures of the P c states. Discussions and predictions based on the calculations are also given.