Question

Write the formula for each of the following compounds: a. sodium oxide b. sodium peroxide c. potassium cyanide d. copper(II) nitrate e. selenium tetrabromide f. iodous acid g. lead(IV) sulfide h. copper(I) chloride i. gallium arsenide j. cadmium selenide k. zinc sulfide l. nitrous acid m. diphosphorus pentoxide

Short answer

a. Na₂O b. Na₂O₂ c. KCN d. Cu(NO₃)₂ e. SeBr₄ f. HIO g. PbS₂ h. CuCl i. GaAs j. CdSe k. ZnS l. HNO₂ m. P₂O₅

Step-by-step solution

a. Sodium oxide

The sodium oxide compound consists of a sodium ion, Na⁺, and an oxide ion, O²⁻. To balance the charges, the formula should have one sodium ion and one oxide ion. So the chemical formula for sodium oxide is Na₂O.

b. Sodium peroxide

Sodium peroxide, the compound is made up of a sodium ion, Na⁺, and a peroxide ion, O₂²⁻. To balance the charges, the formula should have two sodium ions and one peroxide ion. Thus, the chemical formula for sodium peroxide is Na₂O₂.

c. Potassium cyanide

Potassium cyanide is formed by the combination of a potassium ion, K⁺, and a cyanide ion, CN⁻. Here, both ions have equal and opposite charges. So the chemical formula for potassium cyanide is KCN.

d. Copper(II) nitrate

Copper(II) nitrate has a copper ion with a +2 charge (Cu²⁺) and a nitrate ion with a -1 charge (NO₃⁻). To balance the charges, we have one copper ion and two nitrate ions. Thus, the chemical formula for copper(II) nitrate is Cu(NO₃)₂.

e. Selenium tetrabromide

In selenium tetrabromide, Selenium has a -4 charge (Se⁴⁻) and bromine has a +1 charge (Br⁺). To balance the charges, there should be four bromine ions and one selenium ion. The chemical formula for selenium tetrabromide is SeBr₄.

f. Iodous acid

Iodous acid consists of an iodous ion (IO⁺) and a hydrogen ion (H⁺). As IO⁺ and H⁺ have equal and opposite charges, the chemical formula for iodous acid is HIO.

g. Lead(IV) sulfide

Lead(IV) sulfide is a compound formed by a lead ion with a +4 charge (Pb⁴⁺) and a sulfide ion with a -2 charge (S²⁻). To balance the charges, there should be two sulfide ions and one lead ion, resulting in the chemical formula PbS₂.

h. Copper(I) chloride

Copper(I) chloride is composed of a copper ion with a +1 charge (Cu⁺) and a chloride ion with a -1 charge (Cl⁻). Since both ions have equal and opposite charges, the chemical formula for copper(I) chloride is CuCl.

i. Gallium arsenide

Gallium arsenide is the compound formed between gallium (Ga³⁺) and arsenide (As³⁻). Their charges balance each other so the chemical formula for gallium arsenide is GaAs.

j. Cadmium selenide

Cadmium selenide consists of a cadmium ion (Cd²⁺) and a selenide ion (Se²⁻). Both ions have equal and opposite charges, leading to a chemical formula of CdSe.

k. Zinc sulfide

Zinc sulfide is the compound formed by zinc ion (Zn²⁺) and a sulfide ion (S²⁻). Since their charges are equal and opposite, the chemical formula for zinc sulfide is ZnS.

l. Nitrous acid

Nitrous acid is a compound that includes a hydrogen ion (H⁺) and a nitrite ion (NO₂⁻). Since the charges balance each other, the chemical formula for nitrous acid is HNO₂.

m. Diphosphorus pentoxide

Diphosphorus pentoxide consists of two phosphorus ions (P) and five oxide ions (O²⁻). As both ions have neutral charges, the chemical formula for diphosphorus pentoxide is P₂O₅.

Key concepts

Chemical Formulas

Chemical formulas are essential in chemistry because they express the composition of chemical compounds. Each formula represents how many atoms of each element are present in a compound. By looking at a chemical formula, you can understand the basic structure of the compound. For example, in the chemical formula Na₂O, there are two sodium (Na) atoms for every one oxygen (O) atom. Chemical formulas use subscripts to show the number of atoms.
If there is no subscript next to an element symbol, it means there is only one atom of that element in the formula. Formulas also consider the charges on ions to balance the overall charge. More on that is covered in the Charge Balance section.
To effectively write chemical formulas:

• Identify the ions or atoms involved.
• Maintain the charge balance between positive and negative ions.
• Arrange the elements in a logical order, typically starting with the more electropositive element first.

Ionic Compounds

Ionic compounds are formed when metals and non-metals exchange electrons, resulting in the formation of ions. Metals, which are generally on the left side of the periodic table, lose electrons and become positively charged ions known as cations. Conversely, non-metals, which are on the right side, gain electrons to form negatively charged ions called anions.
These oppositely charged ions attract each other, creating an ionic bond. A great example is sodium oxide (Na₂O), where sodium (Na⁺) gives up an electron to oxygen (O²⁻), forming a stable ionic compound.
Ionic compounds have a few key characteristics:

• They tend to have high melting and boiling points due to the strong attraction between ions.
• They usually form crystalline structures.
• In solution or molten form, they conduct electricity.

Understanding ionic compounds is fundamental because they are ubiquitous in daily life, such as in salts and minerals.

Covalent Compounds

Covalent compounds are formed when two non-metal atoms share electrons to achieve full outer electron shells. This sharing of electrons allows each atom to count the shared electrons as part of its own electron shell, leading to stable configurations.
An example is selenium tetrabromide (SeBr₄), where selenium and bromine atoms share electrons to establish covalent bonds.
Here are some attributes of covalent compounds:

• They typically have lower melting and boiling points compared to ionic compounds.
• They do not conduct electricity as they lack free electrons or ions.
• They often exist as gases, liquids, or soft solids at room temperature.

Understanding covalent bonding is critical, especially when studying molecular biology and organic chemistry, as these disciplines heavily rely on covalent interactions.

Charge Balance

In chemical formulas, charge balance is crucial to ensure the compound is electrically neutral. The principle is that the total positive charges must equal the total negative charges in the compound.
For ionic compounds like copper(II) nitrate, which is written as Cu(NO₃)₂, the copper ion is Cu²⁺ and the nitrate ion is NO₃⁻. To balance charges, two nitrate ions are needed to balance one copper ion.
Charge balance involves:

• Identifying the charges of the ions involved.
• Determining the smallest ratio of ions that results in a neutral compound.
• Writing the formula based on the number of each ion needed to balance the charges.

This concept is foundational in predicting how different chemical species will combine in chemical reactions to form stable compounds. Ensuring proper charge balance is essential in writing or understanding chemical formulas accurately.