Any substance within the universe that has mass (see below) and occupies space is defined as matter. Every matter comprises tiny particles called atoms. thanks to their size, atoms are difficult to check. Not until early during this century did scientists carry out the primary experiments suggesting what an atom is like.


The Structure of Atoms: 

    Objects as small as atoms may be “seen” only indirectly, by using very complex technology like tunneling microscopy. We now know an excellent deal about the complexities of atomic structure, but the straightforward view put forth in 1913 by the Danish physicist Niels Bohr provides a decent starting point. Bohr put forward that all-atom possesses an orbiting cloud of tiny subatomic particles called electrons whizzing around a core just like the planets of a miniature scheme. At the center of every atom may be a small, very dense nucleus formed of 2 (two) other kinds of subatomic particles, protons, and neutrons.

    Within the nucleus, a force that works alone over short subatomic distances holds together the cluster of protons and neutrons. Each proton carries a positive (+) charge, and each electron carries a negative (–) charge. Typically, an atom has 1 (one) electron for each proton. The amount of protons (the atom’s atomic number) determines the chemical character of the atom because it dictates the number of electrons orbiting. The nucleus is in stock for chemical action. Neutrons, as their name implies, possess no charge. 


Atomic Mass:

    The terms weight and mass are often used interchangeably, but they need slightly different meanings. Mass refers to the. Quantity of a substance, while weight refers to the force gravity exerts on a substance. Hence, an object has the same mass whether it's on the planet or the moon, but its weight is going to be greater on the world because the earth’s gravitational force is larger than the moon’s. The atomic mass of an atom is equal to the amount of the masses of its protons and neutrons. Atoms that occur naturally on earth. contain from 1 (one) to 92 (ninety-two) protons and up to 146 (one hundred forty-six) neutrons.

     The measurement of the mass of atoms and subatomic particles in units called daltons. to provide you with inspiration for just how small these units are, note that it takes 602 (six hundred and two) million million billion (6.02 × 1023) daltons to form 1 gram! A proton weighs approximately. 1 dalton is actually 1.009 daltons, as does a neutron (1.007 daltons). In contrast, electrons weigh just one 1840 of a dalton, so their benefaction to the mass of an atom is negligible.


 Isotopes:

     Atoms with identical numbers (that is, the identical number of protons) have identical chemical properties and are said to belong to identical elements. Formally speaking, an element is any substance that can't be softened to any other substance by ordinary chemical means. However, while all atoms of part have the identical number of protons, they may not all have the identical number of neutrons. Atoms of an element that possesses different numbers of neutrons are called isotopes of that element. Most elements in nature exist. as mixtures of various isotopes. Carbon (C), for instance, has3 (three) isotopes, all containing 6 (six) protons. Over, 99% of the carbon found in nature exists as an isotope with six neutrons. Because its total mass is 12 (twelve) daltons (6 (six) from protons plus 6 from neutrons), this isotope is remarked as carbon-12 and symbolized 12C. Most of the remainder of the naturally occurring carbon is carbon-13, an isotope with seven neutrons. The rarest carbon isotope is carbon-14 (fourteen), with eight. neutrons. Unlike the opposite two isotopes, carbon-14 is unstable: its nucleus tends to interrupt up elements with lower atomic numbers. This nuclear breakup, which emits a big amount of energy, is termed disintegration, and isotopes that decay during this fashion are radioactive isotopes. 

     Several radioactive isotopes are more unstable than others and therefore decay further readily. For any given isotope, however, the speed of decay is constant. This rate is sometimes. expressed because of the half-life, the time it takes for one 1/2 the atoms in an exceedingly sample to decay. Carbon-14, for instance, has a half-life of about 5600 years. A sample of carbon-containing 1 (one) gram of carbon-14 today would contain 0.5 (point five) gram of carbon- 14 after 5600 (five thousand and six hundred) years, 0.25 gram 11,200 (eleven thousand and two hundred) years from now, 0.125 gram 16,800 (sixteen thousand and eight hundred) years from now, and so on. By determining the ratios of the various isotopes of carbon and other elements in biological examples and in rocks, scientists are able to accurately determine when these materials formed. 

    While there are many useful applications of radioactivity, there also are harmful side effects that has to be considered in any planned use of radioactive substances. Radioactive substances emit energetic subatomic particles that have the potential to severely damage living cells, creating genetic mutation in their genes, and, at high doses, cell death. Consequently, exposure to radiation is now very carefully controlled and controlled. Scientists who work with radioactivity (basic researchers as well as applied scientists like X-ray technologists) wear radiation-sensitive badges to observe the total amount of radioactivity to which they're exposed. Each month the badges are collected and scrutinized. Thus, employees whose workplaces them at risk of excessive radioactive exposure are equipped with an “early warning system.”


Electrons:

     The positive charges within the nucleus of an atom are counterbalanced by charged electrons orbiting at varying distances round the nucleus. Thus, atoms with the same amount of protons and electrons are electrically neutral, having no net charge. Their attraction maintains electrons in their orbits to the charged nucleus. Sometimes other forces overcome this attractor and an atom loses one or more electrons. In other cases, atoms may gain additional electrons. Atoms within which the amount of electrons does not equal the number of protons are referred to as ions, and they carry a net electrical charge. An atom that has more protons than electrons contains a net charge and is called a cation. as an example, an atom of sodium (Na) that has lost one electron becomes a sodium ion (Na+), with a charge of +1. An atom that has fewer protons than electrons carries a net electric charge and is named an anion. A chlorine atom (Cl) that has added one electron becomes a chloride ion (Cl–), with a charge of –1.