Question

Give the name and formula of the compound formed from each pair of elements: (a) cesium and bromine; (b) sulfur and barium; (c) calcium and fluorine.

Short answer

Cesium bromide (CsBr), barium sulfide (BaS), and calcium fluoride (CaF2).

Step-by-step solution

Cesium and Bromine

Determine the symbols and charges for cesium and bromine. Cesium (Cs) is an alkali metal with a charge of +1, and bromine (Br) is a halogen with a charge of -1. Since the charges are equal and opposite, they combine in a 1:1 ratio to form cesium bromide. Therefore, the formula is CsBr.

Sulfur and Barium

Determine the symbols and charges for sulfur and barium. Sulfur (S) is a non-metal commonly forming a charge of -2, and barium (Ba) is an alkaline earth metal with a charge of +2. Since the charges are equal and opposite, they also combine in a 1:1 ratio to form barium sulfide. Therefore, the formula is BaS.

Calcium and Fluorine

Determine the symbols and charges for calcium and fluorine. Calcium (Ca) is an alkaline earth metal with a charge of +2, and fluorine (F) is a halogen with a charge of -1. To balance the charges, two fluorine atoms are needed for every calcium atom, combining in a 1:2 ratio to form calcium fluoride. Therefore, the formula is CaF2.

Key concepts

Chemical Formulas

Chemical formulas represent the types and numbers of atoms in a compound. They're like a recipe showing the elements involved and their proportions. For example, in the compound cesium bromide (CsBr), 'Cs' represents cesium and 'Br' represents bromine.

The formula also shows the ratio in which the atoms combine. Subscripts are used to show how many atoms of each element are present. If no subscript is written, it means there's only one atom of that element. For instance, in calcium fluoride (CaF₂), the subscript '2' after 'F' indicates there are two fluorine atoms for every calcium atom. This balance of atoms is essential to maintaining electrical neutrality in the compound.

Understanding chemical formulas helps in predicting the properties and behavior of compounds. By knowing formulas, you can understand how substances interact, their molecular weight, and how they can combine with other chemicals.

Ionic Compounds

Ionic compounds are formed when atoms transfer electrons to achieve a full outer shell of electrons, resulting in positive and negative ions that attract each other.

They usually form between metals and non-metals. Metals, like cesium and calcium, lose electrons to become positively charged ions (cations). Non-metals, like bromine and fluorine, gain electrons to become negatively charged ions (anions).

For instance, in cesium bromide (CsBr), cesium donates one electron to bromine, forming Cs⁺ and Br^-, respectively. These oppositely charged ions attract each other to form a stable ionic compound.

Ionic bonding leads to the formation of crystal lattice structures which are highly stable and have high melting and boiling points due to the strong ionic bonds. These compounds also tend to be soluble in water and can conduct electricity when dissolved or melted.

Element Charges

Element charges, or oxidation states, indicate how many electrons an element tends to gain or lose to achieve a stable electron configuration. This is essential for predicting how elements combine in compounds.

Alkali metals like cesium (Cs) have a charge of +1 because they lose one electron, becoming cations. Alkaline earth metals like calcium (Ca) and barium (Ba) have charges of +2 because they lose two electrons.

On the other hand, non-metals like bromine (Br) and fluorine (F) have negative charges. Bromine tends to gain one electron to form a charge of -1, while sulfur (S) commonly gains two electrons to achieve a charge of -2.

When writing formulas, it’s crucial to balance these charges. For example, in calcium fluoride (CaF₂), calcium has a +2 charge, and each fluorine has a -1 charge. Two fluorine ions are needed to balance one calcium ion, resulting in CaF₂.

Knowing the charges helps in predicting and balancing chemical equations, ensuring that the compounds formed are electrically neutral.