Question

Write the formulas for the following compounds, and indicate the oxidation state of the group 4 A element or of boron in each: (a) boric acid, (b) silicon tetrabromide, (c) lead(II) chloride, (d) sodium tetraborate decahydrate \((\) borax \(),(e)\) boric oxide.

Short answer

The formulas for each compound and corresponding oxidation states are as follows: (a) Boric acid: Formula is H3BO3 with boron oxidation state of +3. (b) Silicon tetrabromide: Formula is SiBr4 with silicon oxidation state of +4. (c) Lead(II) chloride: Formula is PbCl2 with lead oxidation state of +2. (d) Sodium tetraborate decahydrate (borax): Formula is Na2B4O7·10H2O with boron oxidation state of +3. (e) Boric oxide: Formula is B2O3 with boron oxidation state of +3.

Step-by-step solution

Write the formulas for each compound

For each compound, we can use the information given to identify the elements and their respective charges. (a) boric acid: In boric acid, there is boron (B) and a hydroxide group (OH). Boron is in group 13, while hydrogen and oxygen are in groups 1 and 16, respectively. The formula of boric acid is H3BO3. (b) silicon tetrabromide: In silicon tetrabromide, there is one silicon (Si) atom and four bromine (Br) atoms. Silicon is in group 14, while bromine is in group 17. The formula for silicon tetrabromide is SiBr4. (c) lead(II) chloride: The Roman numeral (II) indicates that lead (Pb) has a charge of +2 in this compound. It is combined with chloride (Cl), which has a charge of -1, resulting in the formula PbCl2. (d) sodium tetraborate decahydrate (borax): This compound consists of sodium (Na), boron (B), oxygen (O) and water (H2O). Sodium is in group 1, boron is in group 13, and oxygen is in group 16. The formula for this compound is Na2B4O7·10H2O. (e) boric oxide: Again, there is boron (B) in this compound, along with oxygen (O). The formula of boric oxide is B2O3.

Determine the oxidation state of the group 4 A element or boron in each compound

Now, we will determine the oxidation state of each applicable element in the compounds. (a) boric acid (H3BO3): The oxidation state of the boron is +3, as it is combined with three hydroxide ions, each with a charge of -1. (b) silicon tetrabromide (SiBr4): The oxidation state of silicon is +4, as silicon is in group 14 and is combined with four bromine atoms, each with a charge of -1. (c) lead(II) chloride (PbCl2): The Roman numeral (II) in the name 'lead(II) chloride' indicates that lead has an oxidation state of +2. (d) sodium tetraborate decahydrate (borax) (Na2B4O7·10H2O): In this compound, the four boron atoms each have an oxidation state of +3, as they are combined with seven oxygen atoms, each with a charge of -2, and two sodium atoms, each with a charge of +1. (e) boric oxide (B2O3): In boric oxide, the oxidation state of each boron atom is +3, as they are combined with three oxygen atoms, each with a charge of -2.

Key concepts

Chemical Formulas

Understanding chemical formulas is crucial for comprehending the composition of compounds. A chemical formula is a shorthand way of representing the elements and the number of atoms of each element present in a compound. It's like a recipe for the compound, telling you exactly what and how much you need of each ingredient. For example, the formula for boric acid, H3BO3, indicates that each molecule is made up of 3 hydrogen atoms, 1 boron atom, and 3 oxygen atoms.

When decoding chemical formulas, it’s important to recognize that the subscript numbers reflect the ratio of atoms within the compound. If no subscript is written, it implies that there is only one atom of that element in the compound. Furthermore, certain formulas can also include symbols to indicate the state of the compound (solid, liquid, gas), or the presence of water molecules, like in sodium tetraborate decahydrate (borax), which contains water of crystallization as indicated by '·10H2O'.

Oxidation Numbers

Oxidation numbers, also known as oxidation states, are a way of keeping track of electrons in chemical reactions, particularly redox reactions. These numbers help us understand the transfer of electrons between atoms and can indicate the degree of oxidation of an atom. When determining the oxidation number of an element in a compound, we look at the charge it would have if all bonds were completely ionic.

For instance, the oxidation number of boron in boric acid (H3BO3) is +3, and in boric oxide (B2O3) also +3; this indicates that boron, which normally has zero charge as an element, is 'losing' three electrons when forming these compounds. Different rules are used to assign oxidation states, such as the fact that the sum of the oxidation states for all atoms in a neutral molecule must equal zero. Understanding oxidation numbers is vital for balancing chemical equations and for identifying the roles of various substances in redox reactions.

Group 4A Elements

Group 4A elements, also referred to as the carbon group, include carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). These elements have a similar outer electron configuration, which gives them a common +4 oxidation state, although they can also exhibit other oxidation states. In the exercise, we encounter silicon in silicon tetrabromide (SiBr4) where silicon has a +4 oxidation number, bonding with four bromine atoms, each with a -1 charge.

The diversity in chemical behavior amongst Group 4A elements is noteworthy; for example, carbon forms the basis of all known life on Earth due to its ability to create complex and stable molecules, while silicon is the second most abundant element in the Earth's crust and is widely used in semiconductor technology. Understanding the properties of Group 4A elements is, therefore, fundamental to exploring various fields like organic chemistry and materials science.

Boron Chemistry

Boron chemistry is fascinating due to boron's unique properties and its position in the periodic table. Located in group 13, boron has only three electrons to share, which can lead to electron-deficient compounds unlike the other elements typically encountered in general chemistry. This electron deficiency enables boron to form compounds which can act as Lewis acids, such as in the case of boric acid (H3BO3) and boric oxide (B2O3).

In the exercise, we focus on compounds where boron has a +3 oxidation state. Boron's ability to form stable covalent bonds with oxygen is characteristic of its chemistry, often resulting in the formation of borate anions which can create vast networks of boron-oxygen structures. Sodium tetraborate decahydrate, commonly known as borax (Na2B4O7·10H2O), is an example that showcases boron's capacity to form intricate structures with both boron-oxygen bonds and hydrated water molecules.