The name of a metal ion is the same as the name of the metal atom from which it forms, so Ca 2+ is called a calcium ion. It has the same number of electrons as atoms of the preceding noble gas, argon, and is symbolized Ca 2+. This results in a cation with 20 protons, 18 electrons, and a 2+ charge. For example, a neutral calcium atom, with 20 protons and 20 electrons, readily loses two electrons. To illustrate, an atom of an alkali metal (Group 1) loses one electron and forms a cation with a 1+ charge an alkaline earth metal (Group 2) loses two electrons and forms a cation with a 2+ charge, and so on. ![]() They form cations with a charge equal to the group number. Moving from the far left to the right on the periodic table, atoms of main-group metals lose enough electrons to leave them with the same number of electrons as an atom of the preceding noble gas. The periodic table helps to predict whether an atom will form an anion or a cation, and also the charge of the resulting ion. Likewise, when an atom gains electrons, it forms a negative ion called an anion. Cations have more protons than electrons. When an atom loses electrons, it forms a positive ion called a cation. During the formation of some compounds, atoms gain or lose electrons to form electrically charged particles called ions. ![]() The transfer and sharing of electrons among atoms govern the chemistry of the elements. Electrons, however, can be added to atoms by transfer from other atoms, lost by transfer to other atoms, or shared with other atoms. In ordinary chemical reactions, the nucleus - which contains the protons and neutrons of each atom and thus identifies the element - remains unchanged.
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