![]() ![]() This can similarly be said about the protons pulling the electrons closer to the nucleus, which as a result decreases atomic size.įigure 3 below depicts this process. If ten magnets and ten metallic objects represent a neutral atom where the magnets are protons and the metallic objects are electrons, then removing one metallic object, which is like removing an electron, will cause the magnet to pull the metallic objects closer because of a decrease in number of the metallic objects. An analogy to this can be of a magnet and a metallic object.It will also decrease because there are now less electrons in the outer shell, which will decrease the radius size. This will cause a decrease in atomic size because there are now fewer electrons for the protons to pull towards the nucleus and will result in a stronger pull of the electrons towards the nucleus. The loss of an electron means that there are now more protons than electrons in the atom, which is stated above.The loss in an electron will consequently result in a change in atomic radii in comparison to the neutral atom of interest (no charge). The cation, which is an ion with a positive charge, by definition has fewer electrons than protons.In contrast, anions have bigger ionic radii than their corresponding neutral atoms. This process can be applied to other examples of ionic radius.Ĭations have smaller ionic radii than their neutral atoms. So, if we had the compound CaSe, which had a total distance of 278 pm between the nucleus of the Ca atom and Se atom, then the atomic radius of the Ca atom will be 278 pm (total distance) - 178 pm (distance of Se), or 100 pm. If we were able to determine the atomic radius of an atom from experimentation, say Se, which had an atomic radius of 178 pm, then we could determine the atomic radius of any other atom bonded to Se by subtracting the size of the atomic radius of Se from the total distance between the two nuclei. The valence electrons are held closer towards the nucleus of the atom.\)decreases going down a group and right to left across the periodic table, the atomic radius will increase going down a group and right to left across the periodic table. This means that the nucleus attracts the electrons more strongly, pulling the atom's shell closer to the nucleus. The effect of increasing proton number is greater than that of the increasing electron number therefore, there is a greater nuclear attraction. However, at the same time, protons are being added to the nucleus, making it more positively charged. This is because, within a period or family of elements, all electrons are added to the same shell. Atomic radius patterns are observed throughout the periodic table.Ītomic size gradually decreases from left to right across a period of elements. The covalent radii of these molecules are often referred to as atomic radii. Nevertheless, it is possible for a vast majority of elements to form covalent molecules in which two like atoms are held together by a single covalent bond. Some are bound by covalent bonds in molecules, some are attracted to each other in ionic crystals, and others are held in metallic crystals. However, this idea is complicated by the fact that not all atoms are normally bound together in the same way. The atomic radius is one-half the distance between the nuclei of two atoms (just like a radius is half the diameter of a circle). This is caused by the increase in atomic radius. Electron affinity decreases from top to bottom within a group.This is caused by the decrease in atomic radius. Electron affinity increases from left to right within a period.This causes the electron to move closer to the nucleus, thus increasing the electron affinity from left to right across a period. ![]() ![]() Moving from left to right across a period, atoms become smaller as the forces of attraction become stronger. With a larger distance between the negatively-charged electron and the positively-charged nucleus, the force of attraction is relatively weaker. This means that an added electron is further away from the atom's nucleus compared with its position in the smaller atom. \( \newcommand\): Periodic Table showing Electron Affinity TrendĮlectron affinity generally decreases down a group of elements because each atom is larger than the atom above it (this is the atomic radius trend, discussed below). ![]()
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