Thus, the columns of the periodic table represent the potential shared state of these elements' outer electron shells that is responsible for their similar chemical characteristics. When an atom gains an electron to become a negatively-charged ion this is indicated by a minus sign after the element symbol for example, \(F^-\). Group 17 elements, including fluorine and chlorine, have seven electrons in their outermost shells they tend to fill this shell by gaining an electron from other atoms, making them negatively-charged ions. When an atom loses an electron to become a positively-charged ion, this is indicated by a plus sign after the element symbol for example, Na +. As a result of losing a negatively-charged electron, they become positively-charged ions. A Bohr model of a chlorine atom shows a nucleus surrounded by three concentric rings. This means that they can achieve a stable configuration and a filled outer shell by donating or losing an electron. Bohr’s model of the hydrogen atom started from the planetary model, but he added one assumption regarding the electrons. Inserting the expression for the orbit energies into the equation for E gives. In this expression, k is a constant comprising fundamental constants such as the electron mass and charge and Planck’s constant. In comparison, the group 1 elements, including hydrogen (H), lithium (Li), and sodium (Na), all have one electron in their outermost shells. Bohr’s expression for the quantized energies is: E n k n 2, n 1, 2, 3. Their non-reactivity has resulted in their being named the inert gases (or noble gases). As shown in, the group 18 atoms helium (He), neon (Ne), and argon (Ar) all have filled outer electron shells, making it unnecessary for them to gain or lose electrons to attain stability they are highly stable as single atoms. The periodic table is arranged in columns and rows based on the number of electrons and where these electrons are located, providing a tool to understand how electrons are distributed in the outer shell of an atom. They also help us explain and predict the behavior of atoms. Models help us visualize atomic structure. It came into existence with the modification of Rutherford’s model of an atom. Atoms are way too small to see with the naked eye (and even most microscopes). The Bohr model of the atom was proposed by Neil Bohr in 1915. Elements in other groups have partially-filled valence shells and gain or lose electrons to achieve a stable electron configuration.Īn atom may gain or lose electrons to achieve a full valence shell, the most stable electron configuration. The Bohr model Google Classroom Learn how Bohr models are used to represent atoms. A full valence shell is the most stable electron configuration. Group 18 elements (helium, neon, and argon are shown) have a full outer, or valence, shell. \):īohr diagrams indicate how many electrons fill each principal shell.
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