While the atomic number, the number of protons in the nucleus, never changes, some electrons are easily lost or gained by an atom. When an atom gains or loses an electron, the atom no longer has a balanced charge.
Therefore, the atom is no longer neutral. An ion is a charged atom. An atom that has gained negatively charged electrons becomes negative. A negative ion or anion is an atom that has gained electrons. An atom that has lost negatively charged electrons becomes positive.
A positive ion or cation is an atom that has lost electrons. Nonmetals tend to gain electrons and become anions. For example, in Fig. This gives it two more negative charges than positive charges and an overall charge of 2—. Metal elements tend to lose electrons and become cations.
Group 18 elements, the noble gases, are very stable non-reactive. This is because they have completely full valence electron shells.
The octet rule states that regardless of how many electrons a shell can potentially hold, the valence shell can only hold eight electrons. The noble gases have eight electrons in their valence shells. Other elements will gain or lose electrons to achieve completely full valence shells, eight electrons in the valence shell, so that they are also stable.
In Fig. The periodic table can help in predicting the type of ion that an element will form based on how many electrons need to be gained or lost for it to become stable. Elements will gain or lose electrons to have the same configuration as a noble gas, in other words, to have a full octet. Atoms tend to gain or lose the least number of electrons to achieve a full octet. In other words, if an atom could lose one electron or gain seven to have a full octet, it will lose one.
Some elements can form ions with two or more different charges. A positive ion, or cation, has the same name as the element. A neutral chlorine Cl atom that gains one electron changes into a chloride ion Cl - with a charge of 1— see Table 2.
Aluminum and carbon react to form an ionic compound. The nature of the attractive forces that hold atoms or ions together within a compound is the basis for classifying chemical bonding. When electrons are transferred and ions form, ionic bonds result.
Ionic bonds are electrostatic forces of attraction, that is, the attractive forces experienced between objects of opposite electrical charge in this case, cations and anions. Covalent bonds are the attractive forces between the positively charged nuclei of the bonded atoms and one or more pairs of electrons that are located between the atoms. Compounds are classified as ionic or molecular covalent on the basis of the bonds present in them.
When an element composed of atoms that readily lose electrons a metal reacts with an element composed of atoms that readily gain electrons a nonmetal , a transfer of electrons usually occurs, producing ions. The compound formed by this transfer is stabilized by the electrostatic attractions ionic bonds between the ions of opposite charge present in the compound.
A compound that contains ions and is held together by ionic bonds is called an ionic compound. The periodic table can help us recognize many of the compounds that are ionic: When a metal is combined with one or more nonmetals, the compound is usually ionic.
This guideline works well for predicting ionic compound formation for most of the compounds typically encountered in an introductory chemistry course. However, it is not always true for example, aluminum chloride, AlCl 3 , is not ionic. You can often recognize ionic compounds because of their properties. Ionic compounds are solids that typically melt at high temperatures and boil at even higher temperatures. When molten, however, it can conduct electricity because its ions are able to move freely through the liquid Figure 3.
Figure 3. Many compounds do not contain ions but instead consist solely of discrete, neutral molecules. These molecular compounds covalent compounds result when atoms share, rather than transfer gain or lose , electrons. Covalent bonding is an important and extensive concept in chemistry, and it will be treated in considerable detail in a later chapter of this text. We can often identify molecular compounds on the basis of their physical properties.
At the ideal interatomic distance, attraction between these particles releases enough energy to facilitate the reaction. Most ionic compounds tend to dissociate in polar solvents because they are often polar. This phenomenon is due to the opposite charges on each ion. In this example, the sodium atom is donating its 1 valence electron to the chlorine atom.
This creates a sodium cation and a chlorine anion. Notice that the net charge of the resulting compound is 0. In this example, the magnesium atom is donating both of its valence electrons to chlorine atoms. Each chlorine atom can only accept 1 electron before it can achieve its noble gas configuration; therefore, 2 atoms of chlorine are required to accept the 2 electrons donated by the magnesium. Notice that the net charge of the compound is 0.
Covalent bonding is the sharing of electrons between atoms. This type of bonding occurs between two atoms of the same element or of elements close to each other in the periodic table.
This bonding occurs primarily between nonmetals; however, it can also be observed between nonmetals and metals.
If atoms have similar electronegativities the same affinity for electrons , covalent bonds are most likely to occur. Because both atoms have the same affinity for electrons and neither has a tendency to donate them, they share electrons in order to achieve octet configuration and become more stable. In addition, the ionization energy of the atom is too large and the electron affinity of the atom is too small for ionic bonding to occur.
For example: carbon does not form ionic bonds because it has 4 valence electrons, half of an octet. To form ionic bonds, Carbon molecules must either gain or lose 4 electrons. What do the terms anhydrous, hydrous, and undissociated mean?
What are ionic compounds? How can I identify ionic compounds? Why are ionic compounds solid at room temperature? See all questions in Ionic Compounds. Impact of this question views around the world. You can reuse this answer Creative Commons License.
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