Scientist - a person learned in science and especially natural science : a scientific investigator
http://www.merriam-webster.com/dictionary/scientist
Science - a: knowledge or a system of knowledge covering general truths or the operation of general laws especially as obtained and tested through scientific method b: such knowledge or such a system of knowledge concerned with the physical world and its phenomena.
http://www.merriam-webster.com/dictionary/science
Natural science - any of the sciences (as physics, chemistry, or biology) that deal with matter, energy, and their interrelations and transformations or with objectively measurable phenomena
http://www.merriam-webster.com/dictionary/natural+science
Physics and chemistry are considered 'pure science' (implying to me more of a theoretical aspect) as opposed to Engineering which is an applied science.
Are Engineers scientists? To some extent yes.
Some engineers are involved mainly in application and the support of application. Other engineers do research to better understand the system or element that is being engineered.
I'm classified as an engineer, and so are my colleagues, yet we do a fair amount of research into the physics of materials (thermophysical/thermomechanical) and effects of radiation. We take experimental results and transform them into mathematical models, which are then integrated into system models with which we make predictions. Based on the success or failure of predictions, we identify shortcomings in the models and experiments, and we propose improved experiments. We also use the models to improve the utilitization of technology.
Our group interfaces with other groups who are involved as users of technology or developers and suppliers of technology, and those groups involves a large population of engineers and scientists of a variety of disciplines in engineering, physics and chemsitry.