Why do ions have a charge

When an atom or molecule gains or loses electrons, it is called an ion. Electrons, being much smaller in mass than protons, do not contribute significantly to the atomic mass. When atoms or molecules lose electrons, they are called cations. Cations have a positive charge because they have more protons, which have a positive charge, than electrons, which have a negative charge.

Cations are given the same name as their element, followed by the word ion. A calcium atom has 20 protons and 20 electrons. It loses two electrons to become a calcium ion with 20 protons and 18 electrons. Because it now has two more positive charges than negative charges, it has an overall charge of positive two.

The chemical symbol for an ion is written as the chemical symbol of the atom with the charge written on the right superscript position. When atoms or molecules gain electrons, they are called anions. Anions have a negative charge because they have more electrons than protons. Anions are named by adding the suffix '-ide' to their element name. A fluorine atom has 9 protons and 9 electrons. Fluorine gains one electron to become a fluoride ion with 9 protons and 10 electrons.

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. 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. Oxygen will gain 2 electrons. In many cases, elements that belong to the same group vertical column on the periodic table form ions with the same charge because they have the same number of valence electrons.

Thus, the periodic table becomes a tool for remembering the charges on many ions. Note the convention of first writing the number and then the sign on a multiply charged ion. These diagrams have two advantages over the electron shell diagrams. First, they show only valence electrons. Second, instead of having a circle around the chemical symbol to represent the electron shell, they have up to eight dots around the symbol; each dot represents a valence electron.

These dots are arranged to the right and left and above and below the symbol, with no more than two dots on a side. For example, the representation for sodium is as follows:. The formula will therefore be MX 2. When something loses electrons we say that it has been oxidised. When something gains electrons, we say it has been reduced. So in ionic bonding, the metals are oxidised and the non-metals are reduced. Forming ions Ions are electrically charged particles formed when atoms lose or gain electrons.

Positively charged sodium and aluminium ions.