 Hello, welcome to the course on Quantum Chemistry of Atoms and Molecules. I am Anindya Datta, Professor of Chemistry IIT Bombay. In our institute, we have several courses on Quantum Chemistry. The first one is CH107, Physical Chemistry 1, in which first year BTEC students are introduced to the concept of Quantum Chemistry. This follows a course or half a course on Quantum Physics. Later on, there is CH425, where first year MSc students and third year BS students study Quantum Chemistry in a little more detail. And then there is CH560, which is a more advanced course on Quantum Chemistry. So, when we started thinking of this course, the NPTEL course, I was wondering where we should pitch it. And the initial thought was that it would be at CH107 level. But the way it turned out is that it is somewhat between CH107 and CH425. So, to translate that to people who are not familiar with our course names, this would be appropriate for students in first year MSc or advanced BSc or any BTEC student who would be interested in learning Quantum Chemistry of Atoms and Molecules. So, the beginning of this course is this. For millennia, humankind had asked the question, what is everything made up of? And different civilizations at different times have come up with different answers. About 100 years or so ago, the science of quantum mechanics evolved as the final answer to this question. And application of quantum mechanics very largely is in understanding what atoms and molecules are made up of. As chemists, we are going to focus on this aspect of quantum mechanics. So, this is not really a hardcore quantum mechanics course. We will not go very deep into the mathematics, but we cannot do it without mathematics either because the language of quantum mechanics is really mathematical. But for those who have not studied mathematics or maybe a little scared of mathematics need not worry, because we are going to develop every mathematical tool that we are going to use in this course. This has been elaborated further in the first lecture itself. So, what we will try to do in this course is that we will start with the very basics of quantum mechanics, why quantum mechanics came into existence first of all. And then we will go on and discuss how quantum numbers come. Most of us would know that there are things called quantum numbers, energy is quantized, angular momentum is quantized. But what we have seen is that even after studying MSc, the concept of the origin of quantization is often not clear. In this course, we will try and see whether we can clear that concept. That is where the focus is on. Then we will discuss some simple systems free particle, particle in a box. We will talk about tunneling. We will talk about harmonic oscillator and rigid rotor and then get into the simplest atom, the hydrogen atom. And there we will come upon another fundamental question that most of us would already be familiar with. We are going to discuss what orbitals are. Everybody has heard of orbitals. But most of the time when we ask a student what is an orbital, we get a very popular incorrect answer, more of that in the actual lectures. Then we will go on and talk about multi-electron atoms and then molecules. In course of doing all this, we will learn some approximation methods like variation method and perturbation theory. And quantum mechanics and spectroscopy go hand in hand. Quantum mechanics is theory. Spectroscopy is the experiment. So we will touch upon a little bit of spectroscopy. Not too much. For that there is another NP-12 course that was offered couple of years ago. Those lectures are already available. So this nutshell is the premise of the course. I hope that students who take this course will enjoy it. And also we will get some very basic questions about quantum chemistry cleared. Hope to see a lot of you in the course. Thank you.