The Atom: The Basics
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The Atom: The Basics

This article covers the basics of the atom, including the structure (protons, neutrons and electrons),ions and isotopes. It is written for novices, but is equally useful for any chemistry student revising the structure of the atom at any level. If you have any questions please feel free to message me.

An atom is a tiny particle, from which everything is made. There are hundreds of different types of atoms, and they're names and basic information is listed in the Periodic Table. 

Atoms are made of 3 subatomic (smaller than an atom) particles. Protons, Neutrons and Electrons.  Protons are positively charged particles that reside in the nucleus, and are given a relative mass of 1. Neutrons are also found in the nucleus, but as their name suggests they are neutral (have no charge). Neutrons also have a relative mass of 1. The 3rd type of particle, electrons, are found outside the nucleus is areas called shells. They are negatively charged, and the shells in which they are arranged make up the majority of the volume of an atom. The mass of an electron is so small, it is normally ignored. It is 2000x less than the mass of a proton.

As the electrons are not located in the nucleus they can be lost, gained or shared between 2 atoms. This is what happens when chemicals react. When electrons are lost/gained the overall charge on the atom changes, and it becomes a charged particle called an ION.  For each electron gained the charge becomes 1 less. For each electron lost the charge becomes 1 more. For example if an atom loses 2 electrons it's charge is 2+, if it gains 1 electron the charges is written as - ( the 1 is left out).  To symbolise this a superscript + or - sign is written after the chemical symbol. 

It's not only electrons which can vary in number in an atom; the number of neutrons in an atom also changes. When atoms have the same number of protons, but a different number of neutrons they are called ISOTOPES of each other.

Isotopes occur naturally, for example Chlorine has 2: chlorine-35 and chlorine-37. The number after atom's name represents the mass number of the atom. The mass number is the number of protons + the number of neutrons. Isotopes have the same chemical properties as each other, because chemical properties are decided by the number and arrangements of electrons. The physical properties of the atom are different, and any property dependant on mass of the atom. For example the reactivity of the isotope will be the same, as the electron arrangement is the same, however boiling and melting points will be higher for a heavier isotope, as more energy is required to move a larger mass (kinetic energy=1/2 mass x velocity squared). 

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