Nonmetals usually form anions.Īlthough a fluoride ion has the same number of electrons as a neon atom, a fluoride ion is different from a neon atom. Negatively charged ions such as F − are called anions. The number 1 is usually not written in the superscript: Because atoms are electrically neutral, a gain of one electron gives a fluoride ion a 1− charge. To get the same number of electrons as a neon atom, a fluorine atom must gain one electron. The noble gas that has an atomic number closest to 9 is neon, with atomic number 10. Consider the fluorine atom, atomic number 9. Nonmetals usually gain electrons when they form ions. Positively charged ions, such as Ca 2+, are called cations. Notice that in the formula for an ion, the charge is written with the number on the left followed by the sign of the charge. Because atoms are electrically neutral, loss of two electrons leaves a calcium ion with a 2+ charge the charge of an ion is written as a right superscript: Therefore, to get the same number of electrons as an argon atom, a calcium atom must lose two electrons. The noble gas that has an atomic number closest to 20, the atomic number of calcium, is argon, with atomic number 18. The atomic number of calcium is 20, and a calcium atom has 20 electrons outside its nucleus. For example, consider the formation of a cacium ion from a calcium atom. Because the total negative charge of the electrons in an atom equals the total positive charge on the nucleus, the loss of electrons leaves an ion with a net positive charge. When atoms of reactive metals such as the elemtns in Group IA (group 1) and the elements toward the bottom of Group IIA (group 2) in the periodic table combine with atoms of nonmetals to form compounds, enough electrons are transferred to give each atom the same number of electrons as the noble gas with the closest atomic number. Ions are charged particles formed by the transfer of electrons from one element or combination of elements to another element or combination of elements.
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