![]() ![]() ![]() 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. Within a period, protons are added to the nucleus as electrons are being added to the same principal energy level. There are some small exceptions, such as the oxygen radius being slightly greater than the nitrogen radius. However, this idea is complicated by the fact that not all atoms are normally bound together in the same way. The atomic radius of atoms generally decreases from left to right across a period. 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 causes the electron to move closer to the nucleus, thus increasing the electron affinity from left to right across a period. A molecules atomic radius decreases over time. Moving from left to right across a period, atoms become smaller as the forces of attraction become stronger. The atomic radius in a periodic table varies as we move across or down the table. Now, at the time of addition of electron to an atom a proton is also added to the nucleus of the atom. Going down the group, the first ionisation. Now, for each period of elements one new electron is being added to the very same shell. Progressing down group 2, the atomic radius increases due to the extra shell of electrons for each element. With a larger distance between the negatively-charged electron and the positively-charged nucleus, the force of attraction is relatively weaker. The very first atomic radius trend is that the size of atom decreases as we move from left to right through a period. 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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