1 Chemistry for Engineering Logistics THE STRUCTURE OF THE ATOM 1. General Information 2. Sub-atomic Particles 3. Rutherford-Bohr Model of the Atom Assoc. Prof. V. Grozev Department “ORGANIC CHEMISRTY AND TECHNOLOGY”

2 The atom is the smallest particle of a chemical element which shows all properties of element. Some characteristics of "atoms" are as follows: - atom takes part in chemical reactions independently; - atom can be divided into a number of sub-atomic particles; - fundamental particles of atom are electron, proton and neutron. Atoms have ability to interact each other and to form a molecule. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. It is the smallest particle of a substance that retains the chemical and physical properties of the substance. 1. General Information

2. Sub - atomic Particles 3 Atoms are made up of three particles: protons, neutrons and electrons. The electron (e - ) has one unit negative charge (-1) and a mass of 1/1836 of the mass of the hydrogen atom. Protons are particles that bear one positive charge (+1) and have a mass approximately equal to one atomic mass unit. Neutrons are particles with no charge and a mass equal to one atomic mass unit. Ernest Rutherford developed a model of the atom, where electrons surround a nucleus of protons and neutrons.

3. Rutherford-Bohr Model of an Atom Main Points of Rutherford- Bohr Model of an Atom 1. At the center of the atom there is a positively charged atomic nucleus. It consist of protons and neutrons. 2. In the electrostatic field of the nucleus move electrons. They constitute the electron shell of the atom. 3. The number of electrons is equal to the number of positive charges in the nucleus and the atom is neutral. (nucleus) n=1 Generic atomic planetary model

3. Rutherford-Bohr Model of the Atom Atomic nuclear The atomic nucleus consist of two types of particles: protons and neutrons. Protons repel each other via electrostatic forces but over a very short range (approximately meters) there exists a very strong force called the nuclear force. This binds the protons and neutrons together into a nucleus. The number of protons in the nucleus is equal to the number of the element in the periodic table Z. Atomic sizes are on the order of m.

3. Rutherford-Bohr Model of the Atom Electronic Shell of the Atom The electrons mooving in the space around the nucleas constitude the electron shell of the atom. The number of electrons is equal to the number of protons in the atomic nucleas Z. The motion of the electrons in electronic shell can be: - around the nucleus; - spin. The moving of electrons around the nuclei is along the orbitals denoted by n=1, n=2, n-3 …Thus the electron shell has a layered structure. The electrons in each orbital have definite fixed energy – E 1 < E 2 < E 3.. Two electrons can be with parallel or with antiparallel spin. The outermost electrons in the shell are called valence electrons. They participate in the formation of a chemical bonds.

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