Bonding Preferences: Videos & Practice Problems

Understanding bonding preferences is crucial in predicting the number of bonds and lone pairs in molecular compounds. Elements in groups 1A to 4A typically form bonds equal to their group number, while those in groups 5A to 7A form bonds based on achieving a stable electron configuration, following the octet rule. For instance, nitrogen forms three bonds, oxygen two, and halogens one. Lone pairs are also significant, with nitrogen having one, oxygen two, and halogens three. This knowledge is foundational for drawing molecular structures and understanding chemical reactivity.

Bonding Preferences Concept 1

Now when it comes to bonding preferences, realize that we can predict the number of bonds and non-bonding electrons in a molecular compound. Now when it comes to these non-bonding electrons, they're just electrons that do not participate in bonding with other elements. And we can say here that a lone pair is just a pair of these non-bonding electrons. Now if we take a look here, we have some common bonding preferences. So we have from groups 1a to 7a, and here we have representative elements for each group. Realize here that when it comes to group 7a, to represent a halogen, I can use the variable of x, which stands in for fluorine, chlorine, bromine, and iodine. Here, when we talk about bonding preferences, we're going to say here that for rule 1, we're gonna say group 1a to 4a elements, it's pretty simple. We're gonna say the number of bonds that they prefer is equal to their group number. So hydrogen, which is in group 1a, preferably wants to make one bond. And one important thing here is when we start drawing molecular compounds later on, realize that when drawing it, hydrogen never goes in the center of any of those compounds. Beryllium is in group 2a, so it wants to make 2 bonds. Boron's in group 3a, so it wants to make 3. Now carbon is incredibly important. Carbon wants to make 4 bonds, even if that means bonding with itself. Now for groups 5a to 7a, we go by rule 2. Here we're going to say that the number of bonds equals the number of electrons needed for a stable electron configuration or arrangement. So, again, groups 1a to 4a, it's based on group number. And then we're going to say here that nitrogen, which is in group 5a, has 5 valence electrons, so it comes in with 5. But if it wants to follow the octet rule, it wants to get to 8 valence electrons. By forming bonds with surrounding elements, it's able to pick up 3 more. So that's why it wants to make 3 bonds. Oxygen's group 6a, so it has 6 valence electrons that it brings to the table, and it picks up the 2 additional ones that it needs by forming 2 bonds to surrounding elements. And then the halogens as surrounding elements only make a single bond. They come in with 7 valence electrons because they're in group 7a. So to pick up that 8th electron they need, they form one bond to a surrounding element. Now if we look here in terms of lone pairs, we're gonna say that the first four have no lone pairs. But then groups 5a to 7a, here we have 1 lone pair on nitrogen, then we have 2 lone pairs on oxygen, and then we have 1, 2, 3 lone pairs on a halogen when it's a surrounding element. So just remember, when it comes to bonding preferences, these are the typical ones that we have for elements from groups 1a to 7a of the periodic table.

Bonding Preferences Example 1

Here it asks, how many bonds and lone pairs are typically found around an oxygen atom? Now we're going to say here, if we look up above, that'd be a little bit of cheating, so let's just think about this. Oxygen is in group 6a. Remember, from elements from groups 5a to 7a, the number of bonds they make is based on how many electrons they need to get to the ideal electron arrangement. Oxygen is in group 6a, so it has 6 valence electrons. If it wants to follow the octet rule to get 8 valence electrons around it, it wants to make 2 bonds, and thereby pick up 2 additional electrons. So here, we can say the number of bonds an oxygen atom typically makes is 2, and then we can say the number of lone pairs around it are 1, 2. These lone pairs are not connecting to another element. So here, definitely the answer is option b.

How many bonds and nonbonding electrons can be found around Si atoms?

• A. 4, 4
• B. 2, 4
• C. 3, 2
• D. 4, 0

Answer: (D)

How many bonds and lone pairs can be found around Mg atoms?
a) 2, 1                    b) 2, 0                    c) 3, 1                     d) 3, 0

• A. 2, 1
• B. 2, 0
• C. 3, 1
• D. 3, 0

Answer: (B)

Here’s what students ask on this topic:

What are bonding preferences for elements in groups 1A to 4A?

Elements in groups 1A to 4A typically form bonds equal to their group number. For example, hydrogen (group 1A) prefers to form one bond, beryllium (group 2A) forms two bonds, boron (group 3A) forms three bonds, and carbon (group 4A) forms four bonds. This pattern helps predict the bonding behavior of these elements in molecular compounds. Additionally, hydrogen never goes in the center of molecular structures. Understanding these preferences is crucial for drawing accurate molecular structures and predicting chemical reactivity.

How do elements in groups 5A to 7A determine their bonding preferences?

Elements in groups 5A to 7A determine their bonding preferences based on achieving a stable electron configuration, following the octet rule. For instance, nitrogen (group 5A) has five valence electrons and needs three more to reach eight, so it forms three bonds. Oxygen (group 6A) has six valence electrons and forms two bonds to achieve a stable configuration. Halogens (group 7A) have seven valence electrons and form one bond to complete their octet. This approach helps predict the number of bonds these elements will form in molecular compounds.

What are lone pairs, and how do they relate to bonding preferences?

Lone pairs are pairs of valence electrons that do not participate in bonding with other elements. They are significant in determining the shape and reactivity of molecules. For example, nitrogen (group 5A) has one lone pair, oxygen (group 6A) has two lone pairs, and halogens (group 7A) have three lone pairs when they are surrounding elements. Understanding the presence of lone pairs is crucial for predicting molecular geometry and chemical behavior.

Why is carbon's bonding preference particularly important in chemistry?

Carbon's bonding preference is particularly important because it can form four bonds, even with itself, leading to a vast array of molecular structures. This versatility is the foundation of organic chemistry, as carbon can create complex molecules like chains, rings, and networks. Carbon's ability to form stable bonds with many elements, including hydrogen, oxygen, and nitrogen, makes it essential for the structure and function of biological molecules and synthetic materials.

How do bonding preferences help in drawing molecular structures?

Bonding preferences help in drawing molecular structures by providing a guideline for the number of bonds each element can form. For example, knowing that hydrogen forms one bond, oxygen forms two, and carbon forms four allows chemists to predict the arrangement of atoms in a molecule. This knowledge is essential for creating accurate Lewis structures, which represent the bonding and lone pairs of electrons in a molecule, and for understanding the molecule's geometry and reactivity.