Final answer:
Group 2 elements of the periodic table, the alkaline earth metals, have two electrons in their outermost s subshell. These include beryllium, magnesium, calcium, strontium, barium, and radium, with a common valence shell electron configuration.
Step-by-step explanation:
The elements that have two electrons are the alkaline earth metals, which belong to Group 2 of the periodic table. These elements include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Each of these elements has two electrons in their outermost s subshell, which is what gives them their distinctive chemical properties such as the ability to form basic or alkaline solutions when dissolved in water.
The valence shell electron configurations of the Group 2 elements reflect their placement in the periodic table. Beryllium (Be), for example, has the electron configuration 1s2 2s2, indicating that its first electron shell is completely filled, and its second shell has two electrons in the 2s subshell. As we move down the group, each element has its inner shells filled according to its atomic number, but they all share the same valence shell electron configuration of having two electrons in the outer s subshell.
It is noteworthy that the alkaline earth metals are less reactive than the alkali metals of Group 1, largely because removing the two valence electrons of Group 2 elements requires more energy.