![]() ![]() The valence electrons are held closer towards the nucleus of the atom. This means that the nucleus attracts the electrons more strongly, pulling the atom's shell closer to the nucleus. This is one of the many modern versions of the Periodic Table. The Periodic Table is shown on the next page in figure 1.4 in its modern form. The effect of increasing proton number is greater than that of the increasing electron number therefore, there is a greater nuclear attraction. On the modern Periodic Table, 112 known elements are arranged in order of increasing atomic numbers with elements with similar properties in the same vertical column. 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. Electron configurations allow us to understand many periodic trends. 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. For example, the electronegativity trend across period 3 in the periodic table is. As we move across a period from left to right the nuclear charge increases and the atomic size decreases, therefore the value of electronegativity increases across a period in the modern periodic table. This means that an added electron is further away from the atom's nucleus compared with its position in the smaller atom. Periodic Trends in the Electronegativities of Elements. \text.\( \newcommand\): 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). The first ionization energy for an element, X, is the energy required to form a cation with +1 charge: The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ( IS 1). ![]()
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