2
Atomic structure and bonding
Learning objectives
After completing this chapter the student should be able to
describe the fundamental concepts of atomic structure;
explain various aspects of chemical bonding;
discuss the relevance of chemical bonding in drug molecules and drug–
receptor interactions.
2.1 Atoms, elements and compounds
The basic building block of all matter is called an atom. Atoms are a
collection of various subatomic particles containing negatively charged
electrons, positively charged protons and neutral particles called neutrons.
Each element has its own unique number of protons, neutrons and electrons.
Both protons and neutrons have mass, whereas the mass of electrons is
negligible. Protons and neutrons exist at the centre of the atom in the
nucleus.
Electrons move around the nucleus, and are arranged in shells at
increasing distances from the nucleus. These shells represent different
energy levels, the outermost shell being the highest energy level.
Chemistry for Pharmacy Students Satyajit D Sarker and Lutfun Nahar
# 2007 John Wiley & Sons, Ltd.