Because it now has one more negative charge than positive charges, it has an overall charge of negative one. The one is usually omitted for ions with a positive or negative one charge. Atoms will lose or gain specific numbers of electrons when forming an ion. Many of the charges for ions formed by the main group elements can be predicted using the periodic table.
The metals, on the left side of the periodic table, will lose electrons. Group 1 alkali metals all lose one electron and have a positive one charge when they become an ion. Group 2 alkaline earth metals lose two electrons and have a positive two charge.
The nonmetals, on the right side of the periodic table, will gain electrons. Group 17 halogens gain one electron and have a negative one charge. Groups 16 elements gain two electrons and will have a negative two charge. Many transition metals can form cations with different charges. Group 18 noble gases do not generally form ions. In ordinary chemical reactions, the nucleus — which contains the protons and neutrons of each atom and thus identifies the element — remains unchanged.
Electrons, however, can be added to atoms by transfer from other atoms, lost by transfer to other atoms, or shared with other atoms. The transfer and sharing of electrons among atoms govern the chemistry of the elements.
During the formation of some compounds, atoms gain or lose electrons to form electrically charged particles called ions. When an atom loses electrons, it forms a positive ion called a cation. Cations have more protons than electrons. Likewise, when an atom gains electrons, it forms a negative ion called an anion.
Anions have more electrons than protons. The periodic table helps to predict whether an atom will form an anion or a cation, and also the charge of the resulting ion. 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.
They form cations with a charge equal to the group number. For example, a neutral calcium atom, with 20 protons and 20 electrons, readily loses two electrons. Moving from the far right to the left on the periodic table, atoms of nonmetal elements generally gain enough electrons to give them the same number of electrons as an atom of the next noble gas in the periodic table.
They form anions with a negative charge equal to the number of groups moved left from the noble gases. For example, the neutral bromine atom, with 35 protons and 35 electrons, can gain one electron to provide it with 36 electrons. The trend between the charge of the ion and position of the group on the periodic table can be used as a guide in many cases.
However, its predictive value decreases when moving toward the center of the periodic table. Transition metals and some other metals often exhibit variable charges that are not predictable by their location in the table. This text is adapted from Openstax, Chemistry 2e, Section 2. To learn more about our GDPR policies click here. If you want more info regarding data storage, please contact gdpr jove. Your access has now expired. Provide feedback to your librarian.
If you have any questions, please do not hesitate to reach out to our customer success team. Non-metal atoms gain an electron, or electrons, to become negatively charged ions. There is a quick way to work out what the charge on an ion should be:. Note 1 : Carbon and silicon in Group 4 usually form covalent bonds by sharing electrons.
Note 2 : The elements in Group 0 do not react with other elements to form ions. Knowing the charges on the ions allows you to work out the formula of an ionic compound. The formula will therefore be MX 2. Atoms that lose electrons acquire a positive charge as a result because they are left with fewer negatively charged electrons to balance the positive charges of the protons in the nucleus. Positively charged ions are called cations.
Most metals become cations when they make ionic compounds. Some atoms have nearly eight electrons in their valence shell and can gain additional valence electrons until they have an octet. When these atoms gain electrons, they acquire a negative charge because they now possess more electrons than protons.
Negatively charged ions are called anions. Most nonmetals become anions when they make ionic compounds. We can use electron configurations to illustrate the electron transfer process between sodium atoms and chlorine atoms.
As demonstrated here, a sodium atom Na has one valence electron in the third principal energy level. It is likely to achieve an octet in its outermost shell by losing its one valence electron. It is now the same as that of the noble gas neon. The term isoelectronic refers to an atom and an ion of a different atom or two different ions that have the same electron configuration.
The sodium ion is isoelectronic with the neon atom. The equation below illustrates this process. When a chlorine atom gains an electron, its outermost principal energy level achieves an octet. In this case, the ion has the same outermost shell as the original atom, but now that shell has eight electrons in it.
Once again, the octet rule has been satisfied. This process is illustrated below. In table salt, this electron comes from the sodium atom. With two oppositely charged ions, there is an electrostatic attraction between them because opposite charges attract. The resulting combination is the compound sodium chloride.
Notice that there are no leftover electrons. The number of electrons lost by the sodium atom one equals the number of electrons gained by the chlorine atom one , so the compound is electrically neutral. In macroscopic samples of sodium chloride, there are billions and billions of sodium and chloride ions, although there is always the same number of cations and anions.
Write the formula of the resulting ion and its electron configuration. The electron configuration of Al atom is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 1. The second shell has octet 2 s 2 2 p 6 while the valence shell has 3 electrons 3 s 2 3 p 1. Mg can achieve octet by losing the 3 valence electrons. The electron configuration of O atom is 1 s 2 2 s 2 2 p 4. The second shell has six electrons 2 s 2 2 p 4 and needs two electrons to achieve octet.
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