Atom Structure - CHEM1101: CHEMISTRY (EEE/COE) Lecture-1...

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Unformatted text preview: CHEM1101: CHEMISTRY (EEE/COE) Lecture-1 ATOMIC STRUCTURE Landmarks in the evolution of atomic structure are: 1805 Daltons atomic theory 1896 Thomson discovery of electron and proton 1909 Rutherfords nuclear atom 1913 Bohrs atomic model 1932 Chadwicks discovery of the neutron Three subatomic particles or principal fundamental particles: Particle Symbol Mass Charge amu grams Units Coulombs Electron e- 1/1835 9.1 10-28-1-1.6 10-19 Proton p + 1 1.672 10-24 +1 +1.6 10-19 Neutron n or n o 1 1.672 10-24 Atomic Theory of Dalton: (1805) 1. All matter is composed of tiny particles called atom which can not be created, destroyed or splitted. 2. All atoms of any one element are identical, have same mass and chemical properties. 3. A compound is a type of matter composed of atoms of two or more elements. 4. A chemical reaction consists of rearranging atoms from one combination to another. British Chemist John Dalton provided the basic theory : all matter- whether element, compound, or mixture- is composed of small particles called atoms. Rutherfords Model of Atom: (1909) AIUB Course-Teacher: Shahrina Alam CHEM1101: CHEMISTRY (EEE/COE) Lecture-1 1. Atom has a tiny dense center core or the NUCLEUS, which contains practically the entire mass of the atom, leaving rest of the atom almost empty. 2. The entire positive charge of the atom is located on the nucleus, while electrons were distributed in vacant space around it. 3. The electrons were moving in orbits or closed circular paths around the nucleus like planets around the sun. Weakness of the Rutherford Atomic Model: According to electromagnetic theory- If a charged particle accelerates around an oppositely charged particle, the former will radiate energy. If an electron radiates energy, its speed will decrease and it will go into spiral motion, finally falling the nucleus, which would make the atom unstable . Contribution: Rutherford laid the foundation of the model picture of atom. Quantum Theory and Bohr Atom: (1913) To understand the Bohr theory, we need to learn- the nature of electromagnetic radiations- the atomic spectra Electromagnetic Radiations: Energy can be transmitted through space by electromagnetic radiations. Some forms of radiant energy are- radio waves- visible light- infrared light- ultraviolet light- x-rays etc. AIUB Course-Teacher: Shahrina Alam CHEM1101: CHEMISTRY (EEE/COE) Lecture-1 Characteristics of Waves: Wavelength ( , lambda): The wavelength is defined as the distance between two successive crests or troughs of a wave. Units : cm, m or (angstrom). 1 = 10-8 cm = 10-10 m, 1 nm = 10-9 m Frequency ( , nu): The frequency is the number of waves which pass a given point in one second....
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Atom Structure - CHEM1101: CHEMISTRY (EEE/COE) Lecture-1...

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