An atom is the smallest part of an element that retains the properties of element. Atoms have a planetary type of structure that consists of central nucleus surrounding by orbiting electrons that have basic negative charge. Nucleus consists of positively charged protons and uncharged particles called neutrons. The basic structure of an atom is shown in figure 1. Figure 1 Bohr model of an atom showing the protons and neutrons, the “tail” is showing the of a motion nucleus. Each type of atom has certain number of electrons and protons that distinguish it from atoms of all other elements Atomic Number All the elements are arranged in periodic table of elements in order of their atomic numbers. Atomic number is equal to number of protons in nucleus that is same as number of electrons in an electrically balanced nucleus. For example atomic number of hydrogen is one that is the number of protons in its nucleus. The atomic number of helium is two.
Electrons Shells and Orbit Electrons orbit the nucleus of an atom at certain distance from the nucleus. Electrons near the nucleus have less energy than those in the more distance orbit. In an atom orbits are group in an energy band known as shells a given atom has a fixed number of shells, and each shell has a fixed number of electrons. The shells are designated 1, 2, 3 and so on with 1 being closest to nucleus. Number of Electrons in Each Shell The maximum number of electrons in each shell is the fact of nature and are calculated by the formula N= 2n2 Where „n‟ is the number of shell. The inner most shell is 1, next is 2 and so on. The maximum number of shells that can exist in 1st shell is N = 2n2 = 2(1)2 = 2 Problem 1 Find the number of electrons in third shell?
Electrons that are in orbit farther from the nucleus have higher energy and are less tightly bound to the atom than those closer to the nucleus. This is...