Valence electrons are the electrons in the outer energy level of an atom that can participate in interactions with other atoms. Valence electrons are generally the electrons that are farthest from the nucleus. As a result, they may be attracted as much or more by the nucleus of another atom than they are by their own nucleus.  Because valence electrons are so important, atoms are often represented by simple diagrams that show only their valence electrons. These are called electron dot diagrams, and three are shown below. In this type of diagram, an elements chemical symbol is surrounded by dots that represent the valence electrons. Typically, the dots are drawn as if there is a square surrounding the element symbol with up to two dots per side. An element never has more than eight valence electrons, so there cant be more than eight dots per atom. Q: Carbon (C) has four valence electrons. What does an electron dot diagram for this element look like? A: An electron dot diagram for carbon looks like this:  The number of valence electrons in an atom is reflected by its position in the periodic table of the elements (see the periodic table in the Figure 1.1). Across each row, or period, of the periodic table, the number of valence electrons in groups 1-2 and 13-18 increases by one from one element to the next. Within each column, or group, of the table, all the elements have the same number of valence electrons. This explains why all the elements in the same group have very similar chemical properties. For elements in groups 1-2 and 13-18, the number of valence electrons is easy to tell directly from the periodic table. This is illustrated in the simplified periodic table in the Figure 1.2. It shows just the numbers of valence electrons in each of these groups. For elements in groups 3-12, determining the number of valence electrons is more complicated. Q: Based on both periodic tables above (Figures 1.1 and 1.2), what are examples of elements that have just one valence electron? What are examples of elements that have eight valence electrons? How many valence electrons does oxygen (O) have? A: Any element in group 1 has just one valence electron. Examples include hydrogen (H), lithium (Li), and sodium (Na). Any element in group 18 has eight valence electrons (except for helium, which has a total of just two electrons). Examples include neon (Ne), argon (Ar), and krypton (Kr). Oxygen, like all the other elements in group 16, has six valence electrons.  The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18
Valence electrons are the electrons in the outer energy level of an atom that can participate in interactions with other atoms . Valence electrons are generally the electrons that are farthest from the nucleus . As a result , they may be attracted as much or more by the nucleus of another atom than they are by their own nucleus . Because valence electrons are so important , atoms are often represented by simple diagrams that show only their valence electrons . These are called electron dot diagrams , and three are shown below . In this type of diagram , an elements chemical symbol is surrounded by dots that represent the valence electrons . Typically , the dots are drawn as if there is a square surrounding the element symbol with up to two dots per side . An element never has more than eight valence electrons , so there ca nt be more than eight dots per atom . Q : Carbon ( C ) has four valence electrons . What does an electron dot diagram for this element look like ? A : An electron dot diagram for carbon looks like this : The number of valence electrons in an atom is reflected by its position in the periodic table of the elements ( see the periodic table in the Figure 1.1 ) . Across each row , or period , of the periodic table , the number of valence electrons in groups 1 - 2 and 13 - 18 increases by one from one element to the next . Within each column , or group , of the table , all the elements have the same number of valence electrons . This explains why all the elements in the same group have very similar chemical properties . For elements in groups 1 - 2 and 13 - 18 , the number of valence electrons is easy to tell directly from the periodic table . This is illustrated in the simplified periodic table in the Figure 1.2 . It shows just the numbers of valence electrons in each of these groups . For elements in groups 3 - 12 , determining the number of valence electrons is more complicated . Q : Based on both periodic tables above ( Figures 1.1 and 1.2 ) , what are examples of elements that have just one valence electron ? What are examples of elements that have eight valence electrons ? How many valence electrons does oxygen ( O ) have ? A : Any element in group 1 has just one valence electron . Examples include hydrogen ( H ) , lithium ( Li ) , and sodium ( Na ) . Any element in group 18 has eight valence electrons ( except for helium , which has a total of just two electrons ) . Examples include neon ( Ne ) , argon ( Ar ) , and krypton ( Kr ) . Oxygen , like all the other elements in group 16 , has six valence electrons . The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature . Instead , they undergo chemical reactions with other elements and form compounds . Table salt is the compound named sodium chloride ( NaCl ) . It forms when an atom of sodium ( Na ) gives up an electron and an atom of chlorine ( Cl ) accepts it . When this happens , sodium becomes a positively charged ion ( Na+ ) , and chlorine becomes a negatively charged ion ( Cl ) . The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions , forming a crystal of salt . Q : Why does sodium give up an electron ? A : An atom of a group 1 element such as sodium has just one valence electron . It is eager to give up this electron in order to have a full outer energy level , because this will give it the most stable arrangement of electrons . You can see how this happens in the animation at the following URL and in the Figure 1.4 . Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason . Q : Why does chlorine accept the electron from sodium ? A : An atom of a group 17 element such as chlorine has seven valence electrons . It is eager to gain an extra electron to fill its outer energy level and gain stability . Group 16 elements with six valence electrons are almost as reactive for the same reason . Atoms of group 18
which element would you expect to gain one electron in a chemical reaction?
which element would you expect to gain one electron in a chemical reaction ?
chlorine
chlorine