Question

Write the Lewis symbol for atoms of each of the following elements: (a) \(\mathrm{Al}\), (b) \(\mathrm{Br}\), (c) \(\mathrm{Ar}\), (d) \(\mathrm{Sr}\).

Short answer

(a) Aluminum: \(\dot{\underset{.}{\text{Al}}}\) (b) Bromine: \(\overset{.}\text{B}\underset{.}{\text{r}}\overset{.}{.}\) (c) Argon: \(\overset{..}\text{A}\overset{..}{\text{r}}\) (d) Strontium: \(\text{S}\overset{.}{\text{r}}.\)

Step-by-step solution

Find the number of valence electrons for each element

Since the number of valence electrons determines how an element forms bonds with other elements, we need to find this for each of the given elements. To do that, we can use the periodic table, where the group number represents the number of valence electrons. (a) Al (Aluminum) is in Group 13, so it has 3 valence electrons. (b) Br (Bromine) is in Group 17, so it has 7 valence electrons. (c) Ar (Argon) is in Group 18, so it has 8 valence electrons. (d) Sr (Strontium) is in Group 2, so it has 2 valence electrons.

Draw the Lewis symbols

Now that we know the number of valence electrons for each element, we can draw the Lewis symbols. We draw the chemical symbol of the element and then surround it with dots representing the valence electrons. (a) Al: The Lewis symbol for aluminum will have three dots around the symbol 'Al' to represent the 3 valence electrons. \[ \dot{\underset{.}{\text{Al}}} \] (b) Br: The Lewis symbol for bromine will have a total of 7 dots around the symbol 'Br' to represent the 7 valence electrons. \[ \overset{.}\text{B}\underset{.}{\text{r}}\overset{.}{.} \] (c) Ar: The Lewis symbol for argon will have 8 dots around the symbol 'Ar' to represent the 8 valence electrons. Note that the maximum number of valence electrons is eight, and once an element has 8 valence electrons, its outer shell is considered to be full, making it very stable and chemically unreactive. \[ \overset{..}\text{A}\overset{..}{\text{r}} \] (d) Sr: The Lewis symbol for strontium will have two dots around the symbol 'Sr' to represent the 2 valence electrons. \[ \text{S}\overset{.}{\text{r}}. \]

Key concepts

Valence Electrons

Understanding valence electrons is critical for students of chemistry, as they are the electrons that participate in chemical bonding. Valence electrons are the electrons in the outermost shell of an atom and determine how an atom can interact with others. For instance, aluminum (Al) has 3 valence electrons, indicating that it can form bonds by losing electrons to achieve a full outer shell.

When drawing Lewis symbols, which are simplified diagrams representing valence electrons, these electrons are depicted as dots around the chemical symbol. The number of dots equals the number of valence electrons; thus, Al would be surrounded by three dots. It's important to evenly distribute these dots to reflect the pairing that occurs as atoms fill their valence shells.

Periodic Table Group

The periodic table is more than just a tabulation of chemical elements; it's a map laying out the intrinsic properties of elements, including which group they belong to. A periodic table group is a column of elements that share the same number of valence electrons, which is key to understanding their chemical behavior.

For example, aluminum (Al) belongs to Group 13 and has 3 valence electrons, while bromine (Br), in Group 17, has 7. Elements in the same group tend to exhibit similar reactivity and bonding characteristics due to their valence electron configuration. This similarity is crucial for predicting how different elements will interact in chemical reactions. When preparing a Lewis symbol, the group number can guide you on the number of valence electrons to include.

Chemical Bonds

Chemical bonds are the glue that holds atoms together in molecules. They form when atoms exchange or share valence electrons to attain a full shell, which is often the most stable electron configuration. Depending on the difference in electronegativity between atoms, the bonds can be ionic (transfer of electrons) or covalent (sharing of electrons).

When looking at Lewis symbols for elements like bromine (Br) with 7 valence electrons, it's evident that it is one electron short of the octet rule, which states that atoms are most stable with 8 valence electrons. Therefore, bromine is likely to form a covalent bond by sharing an electron with another atom to fill its outer shell. Lewis symbols provide a visual representation of the potential bonding situation of an atom, highlighting the primary spots where bonds are likely to occur.