Question

What information is provided by the formula for potassium chromate \(\left(\mathrm{K}_{2} \mathrm{CrO}_{4}\right) ?\)

Short answer

The formula for potassium chromate \( (K_{2}CrO_{4}) \) reveals that it is an ionic compound composed of 2 potassium (K) atoms, 1 chromium (Cr) atom, and 4 oxygen (O) atoms with a ratio of 2:1:4. It also indicates that potassium has a charge of +1 while the chromate ion (CrO₄²⁻) has a charge of -2, resulting in a neutral compound.

Step-by-step solution

Identify the Elements

The formula for potassium chromate is K₂CrO₄. This compound is made up of three different elements: potassium (K), chromium (Cr), and oxygen (O).

Determine the Ratio of Elements

In the formula K₂CrO₄, the subscript numbers indicate the ratio of elements in the compound. There are 2 potassium atoms (K), 1 chromium atom (Cr), and 4 oxygen atoms (O). This shows that potassium chromate has a ratio of 2:1:4 for potassium, chromium, and oxygen, respectively.

Identify the Type of Compound

Potassium chromate is an ionic compound, which means it is formed by the transfer of electrons between a metal and a non-metal element. In this case, potassium (K) is the metal, and chromium and oxygen, which together form the chromate ion (CrO₄²⁻), are the non-metal elements.

Determine the Charges of the Ions

In ionic compounds, the sum of the charges of the positive and negative ions must be equal. Potassium (K) has a charge of +1, and the chromate ion (CrO₄²⁻) has a charge of -2. Since there are two potassium ions in the formula (K₂), the overall positive charge from potassium ions is +2. The overall negative charge from the chromate ion is -2. The sum of the charges is equal (2+(-2)=0), indicating that potassium chromate is a neutral compound. In conclusion, the formula for potassium chromate (K₂CrO₄) provides us with information about the elements present in the compound, the ratio of these elements, the type of compound it is (ionic), and the charges of the ions involved.

Key concepts

Chemical Compound

When we talk about a chemical compound, what we mean is a substance that's made up of two or more different types of elements, which are bonded together in a specific proportion and structure. These bonds can be covalent, where atoms share electrons, or they can be ionic, where one atom donates electrons to another.

Taking potassium chromate as an example, it's a compound composed of potassium (K), chromium (Cr), and oxygen (O). Every chemical compound has unique properties that are different from the elements that it's made from. For instance, while pure potassium is a highly reactive metal, when it combines with chromium and oxygen to form potassium chromate, the resulting compound is much more stable and has distinct chemical and physical properties, such as its color and solubility.

Ionic Compound

Ionic compounds are those formed from the electrostatic attraction between ions, which are charged particles. Ions form when atoms gain or lose electrons to obtain a full outer shell of electrons, leading to stability. In an ionic bond, a metal donates electrons to become a positively charged cation, while a non-metal accepts those electrons to become a negatively charged anion.

Potassium chromate, or \( K_2CrO_4 \), is such a compound where potassium atoms lose electrons to become \( K^+ \) cations and the group of chromium and oxygen atoms gain electrons to form the chromate ion \( CrO_4^{2-} \). The overall charge of the compound is neutral because the total positive charges balance with the total negative charges.

Elemental Ratio

The elemental ratio in a compound tells us how many atoms of each element are present relative to each other. In chemical formulas, subscripts are used to show this ratio. If an element does not have a subscript following it, that implies 'one' atom of that element in the compound.

For potassium chromate, the formula \( K_2CrO_4 \) shows that the elemental ratio of potassium to chromium to oxygen is 2:1:4. This means that for every chromium atom, there are twice as many potassium atoms and four times as many oxygen atoms, giving us insight into the composition and the stoichiometry of the compound – vital information for understanding its reactions and behavior in chemical processes.

Chemical Notation

Chemical notation is a system of symbols and numbers used to represent elements and compounds. It's a shorthand way to convey detailed information about the composition and structure of chemical substances.

For example, in the notation for potassium chromate (\( K_2CrO_4\)), the chemical symbols (K for potassium, Cr for chromium, O for oxygen) are used to identify the elements present. The subscript numbers indicate how many atoms of each element are in one unit of the compound. When no subscript is present, as is the case with chromium in our example, it implies one atom of that element. Notation such as this allows chemists to communicate complex information efficiently and is fundamental for studying and understanding chemistry.