Table of Contents
structure-of-atom
The atom is the smallest particle of an element that has the chemical properties of that element. The atom has a nucleus, which is made up of protons and neutrons, and electrons that orbit the nucleus. The number of protons in an atom’s nucleus determines what element it is.
Introduction to Structure of an Atom
An atom is the smallest particle of an element that has the chemical properties of that element. An atom is made up of a nucleus and electrons. The nucleus is made up of protons and neutrons. Electrons orbit the nucleus. The number of protons in an atom determines what element it is.
Atoms
are the smallest particle of an element that has the chemical properties of that element. They are made up of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus of the atom, and electrons orbit the nucleus. The number of protons in an atom determines what element it is.
Cathode Ray Experiment
In 1897, J.J. Thomson discovered the electron using a cathode ray tube. Thomson placed a metal plate in the path of the cathode ray beam and observed that the beam was bent. He reasoned that the beam was made up of tiny particles that were repelled by the metal plate. These particles were later called electrons.
Electrons
Yes, electrons can be in orbitals. Orbitals are specific regions of space around the nucleus where electrons are likely to be found.
Thomson’s Model of an Atom
Thomson’s model of an atom was the first to propose that atoms were composed of smaller particles. He suggested that atoms were composed of a positively charged nucleus surrounded by negatively charged electrons. This model was later replaced by the Rutherford model.
Radioactivity
Radioactivity is the spontaneous emission of radiation from an unstable nucleus. The nucleus may be natural, as in uranium, or it may be man-made, as in plutonium.
The types of radiation emitted by a nucleus include alpha particles, beta particles, and gamma rays.
Alpha particles are helium nuclei. They are the heaviest and most massive of the types of radiation emitted by a nucleus.
Beta particles are electrons.
Gamma rays are high-energy photons.
Rutherford Model
The Rutherford Model is a model of the atom in which the atom is seen as a small, dense, positively charged nucleus surrounded by a cloud of electrons.
Rutherford’s experiment and s- and p- orbitals
In 1913, Ernest Rutherford performed an experiment in which he directed a beam of alpha particles (helium nuclei) at a thin sheet of gold. He observed that a small percentage of the alpha particles were deflected backwards, while the majority passed straight through the gold. Rutherford concluded that the alpha particles were scattered by the positive nuclei of the gold atoms.
He also observed that the alpha particles that were deflected backwards were scattered more than the others. This indicated that the positive nuclei were concentrated in the center of the atom, and that the electrons were orbiting around the nucleus in a thin shell.
The Rutherford model of the atom is based on these observations. It proposes that the atom consists of a small, positively charged nucleus surrounded by a cloud of negatively charged electrons.
Rutherford’s Model of An Atom
John Dalton proposed the first atomic model in 1803. He suggested that atoms were solid spheres with no empty space inside them.
In 1911, Rutherford proposed a new model of the atom. He suggested that the atom was mostly empty space, with a small, dense nucleus in the center. The electrons orbited around the nucleus like planets around the sun.
Drawbacks of Rutherford’s Model
The Rutherford model has several drawbacks.
1. It does not account for the electron’s spin.
2. It does not explain the origin of the electron’s negative charge.
3. It does not explain why the electron does not fly out of the atom.
Neil Bohr Model
The Bohr model is a simple model of the atom that was developed by Niels Bohr in 1913. In the Bohr model, the electron orbits the nucleus in fixed shells. The Bohr model is a good model of the atom because it explains the emission and absorption of light by atoms.
Properties of Electrons, Protons, and Neutrons
Electrons have a negative charge, protons have a positive charge, and neutrons have no charge.
Orbits
The Earth orbits the sun once a year. It takes 365.24 days for the Earth to go around the sun. This is called a year.
The moon orbits the Earth once a month. It takes 29.5 days for the moon to go around the Earth. This is called a month.
Electron Distribution in Different Orbits
The electron distribution in different orbits is shown in the following figure.
In the ground state, the electron is most likely to be found near the nucleus. In the first excited state, the electron is more likely to be found in the outermost orbit. As the energy of the electron increases, the electron is more likely to be found in increasingly inner orbits.
Valency
A valence is the number of chemical bonds that a particular atom can form. The valence of an atom is determined by the number of electrons in its outermost energy level.
Atomic Number
:
27
Atomic Symbol:
Fe
Atomic Weight:
55.845
Description:
Iron is a silver-white metal that is very common on Earth. It is the most commonly used metal in the world. It is found in many minerals, including hematite and magnetite.
Mass Number and Representation of an Atom
A typical atom has a mass number of about 1.7 × 10-27 kg.
Isotopes and Isobars
The terms isotope and isobar are both used in chemistry. An isotope is a type of atom that has the same number of protons in its nucleus but a different number of neutrons. For example, carbon-12 and carbon-14 are both isotopes of carbon because they have the same number of protons (6), but carbon-14 has 2 more neutrons than carbon-12. Isobars are atoms that have the same number of protons in their nucleus but a different number of electrons.
Calculation of Mass Number for Isotopic Elements
The mass number for an isotopic element is found by adding the atomic masses of the isotopes of that element.
