This study explores the potential of Generative AI chatbots (GenAIbots) such as ChatGPT and Bing Chat, in Chemistry education, within a constructionist theoretical framework. A single-case study methodology was used to analyse extensive interaction logs between students and both AI systems in simulated Chemistry learning experiences. The results highlight the ability of ChatGPT and Bing Chat to act as 'agents-to-think-with', fostering critical thinking, problem-solving, concept comprehension, creativity, and personalised learning experiences. By employing a Socratic-like questioning approach, GenAIbots nurture students' curiosity and promote active learning. The study emphasises the significance of prompt crafting, a technique to elicit desired responses from GenAIbots, fostering iterative reflections and interactions. It underlines the need for comprehensive educator training to effectively integrate these tools into classrooms. The study concludes that while ChatGPT and Bing Chat as agents-to-think-with offer promising avenues to revolutionise STEM education through a constructionist lens, fostering a more interactive, inclusive learning environment and promoting deeper comprehension and critical thinking in students across diverse Chemistry topics, ChatGPT consistently outperformed Bing Chat, providing more comprehensive, detailed, and accurate responses and skillfully addressing nuances and context.