Question

Draw Lewis structures for each of the following elements. Which element is most chemically stable? a. C b. \(\mathrm{Ne}\) c. \(\mathrm{Ca}\) d. \(\mathrm{F}\)

Short answer

Carbon has four dots, neon has eight dots in pairs, calcium has two dots, and fluorine has seven dots around their symbols. Neon is the most chemically stable due to its full valence shell.

Step-by-step solution

Drawing Lewis Structures for Carbon (C)

Carbon has four valence electrons. Represent the element C with its symbol and draw four dots around it, one on each side, representing the four valence electrons.

Drawing Lewis Structures for Neon (Ne)

Neon has eight valence electrons. Draw the symbol Ne and place eight dots around it, in pairs on each of the four sides, to represent the full valence shell.

Drawing Lewis Structures for Calcium (Ca)

Calcium has two valence electrons. Write the symbol Ca and place one dot on two different sides to represent the two valence electrons.

Drawing Lewis Structures for Fluorine (F)

Fluorine has seven valence electrons. Draw the symbol F and place seven dots around it, with three sides having a pair of electrons and one side having a single electron.

Determining the Most Chemically Stable Element

The most chemically stable element is the one with a full valence shell. Neon (Ne) has a complete octet, which makes it the most stable among the given elements.

Key concepts

Chemical Stability

Chemical stability refers to the likelihood that a chemical species will remain unchanged over time or under certain conditions. This stability is often associated with the concept of being unreactive or resistant to chemical change. The stability of an element can be deduced from its Lewis structure, a diagrammatic representation that shows the distribution of valence electrons around the element's symbol.

For instance, when we draw the Lewis structure for neon (Ne), which has a full valence shell of eight electrons, we find that Ne is unlikely to gain or lose electrons, making it chemically inert or stable. This is in sharp contrast to elements which do not have full valence shells, such as calcium (Ca), with only two valence electrons, or fluorine (F), with seven; these elements are more inclined to react in order to achieve a full octet, which is a preferred state for most chemical elements.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom that are available for bonding with other atoms. These electrons play a crucial role in chemical reactions and determine the bonding pattern of an element. The number of valence electrons an element has can often be determined by its group number in the periodic table.

As demonstrated in the exercise, carbon (C) has four valence electrons, which prompts it to form four bonds to achieve a full octet. On the other hand, calcium (Ca) has two valence electrons, often leading it to lose these electrons to achieve a stable state, similar to that of the noble gases. This desire to either gain, lose or share electrons to achieve a full valence shell is foundational to understanding chemical bonding and reactivity.

The Octet Rule

The octet rule is a chemical rule of thumb that states that atoms tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The rule applies to the main-group elements, especially carbon, nitrogen, oxygen, and the halogens, but there are exceptions to the rule.

The rule is based on the stability of the noble gases, which, with the exception of helium, have eight electrons in their outermost shell. For example, in the Lewis structure exercise, neon (Ne) already possesses a complete octet, which explains its lack of reactivity and high chemical stability. In contrast, fluorine (F), which has seven valence electrons, is one electron short of an octet and is highly reactive, often forming a bond to obtain its eighth electron. Understanding the octet rule helps students predict the types of ions or molecules that atoms can form to reach a more energetically favorable, stable state.