A compound can be represented by a chemical formula. Chemical formulas can be divided into three categories: empirical, molecular, and structural. The number of each type of atom in a molecule is shown by molecular formulas, the simplest whole-number ratio of the atoms in a compound is shown by empirical formula, and structural formulas show the bonds between the atoms in a molecule. In this article, we will study what are the different ways to represent compounds. Let's first take a brief look at chemical symbols and valency before learning how to write chemical formulas.

1. Chemical Symbols and Valency

1.1 Chemical Symbols A symbol is a condensed form that represents an element's atom. Each element is identified by a symbol, which is often the initial letter of the element's Latin or English name written in capital letters. Example: The letter "S" stands for the element sulphur. Similarly, the letter "H" stands for hydrogen. When more than one element's first letter is the same, the elements are instead identified by two letters. The first letter is capitalized, and the second is printed in lowercase. For example, the elements whose first letter is C are copper, cobalt, and carbon. Therefore, the letter C solely stands for carbon, The two letters "Co" stand for cobalt, and the two letters "Cu" stand for copper which is taken from its Latin name cuprum. Chemical symbols of all the elements can be viewed in the periodic table.

1.2 Valency

The combining capacity of an atom or a radical is termed valency.

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The term "valency" refers to how many electrons an atom can accept or lose during a chemical process.

• Metals are typically composed of elements with one, two, or three electrons in their outermost shell. Valence electrons are those present in the outermost shell of an atom. These atoms give up their valence electrons and create positive ions or cations in order to achieve a stable electronic state.

• Typically, non-metals are those substances that have five, six, or seven electrons in their outermost shell. These atoms gain electrons and create negative ions, or anions since they need eight electrons in their outermost orbit to be stable.

2. Different Ways To Represent Compounds

2.1 Empirical Formula A compound's empirical formula is a formula that displays the ratio of the elements contained in the compound but not the precise number of atoms present in the molecule. Subscripts are used next to the element symbols to indicate the ratios. It is often referred to as the simplest formula because the subscripts are the lowest whole integers that represent the ratio of elements.

Example: The chemical formula for glucose is C₆H₁₂O₆. For every mole of carbon and oxygen, there are two moles of hydrogen present. Therefore, CH₂O is the empirical formula for glucose. Ribose has the chemical formula C₅H₁₀O₅. For every mole of carbon and oxygen, there are two moles of hydrogen present. Therefore, the empirical formula of ribose is CH₂O.

2.2 Molecular Formula

Two atoms together chemically form a molecule. The chemical formula for a molecular compound molecular formula specifies the type of atoms that makeup the molecule. A subscript under oxygen in H₂O, for example, indicates that there are two hydrogen atoms present, but no subscript under oxygen indicates that there is just one oxygen atom present.

Example:

  The following can be used to represent the chemical formula: Molecular formula = n × (Empirical formula) where n is an integer multiple.

Example: The empirical formula of a compound is BH3. Its molar mass is 27.7g/mol. Determine the molecular formula of the compound. Solution: Given: Empirical formula = BH₃ Molar mass = 27.7 g/mol Empirical formula molar mass (EFM) = 13.84 g/mol n = Molar mass/Emprical formula mass n = 27.7/13.84 = 2 ∴ Molecular formula = BH₃ × 2 = B₂H₆

2.3 Structural Formula

The number of atoms in each element of the compound is indicated by the molecular formula, but the bonding between the components is not. This information is crucial because two molecules can be isomers of one another while having the same number and atoms in common.

The number of atoms in each element of the compound is indicated by the molecular formula, but the bonding between the components is not. This information is crucial because two molecules can be isomers of one another while having the same number and atoms in common. Chemical compounds are identified using structural formulae. A structural formula is a representation of a molecule that shows how its atoms and chemical bonds are arranged. Structural formulas are frequently depicted diagrammatically and consist of one, two, or three lines connecting atoms represented by elemental symbols to one another. A single covalent bond is represented by one line, whereas double and triple covalent bonds are represented by two and three lines, respectively. There are several kinds of structural formulas. Some describe the three-dimensional arrangement of atoms, while others show the two-dimensional structure. Compounds are sometimes shown as lines with letters, sometimes as groups, and other times as just lines. Writing structural formulas typically involves the following techniques: i. Electron dot structural formula (Lewis dot structure) ii. Expanded structural formula iii. Condensed structural formula iv. Bond-line/Skeletal structural formula

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Key Takeaways

Key Points

• When element symbols are followed by subscripts, the empirical formula determines the least whole number ratio of elements in a compound.

• There are instances where the empirical formula and the molecular formula are identical.

• The principal objective of the empirical formula in experimental chemistry is to enable statisticians to estimate the expected outcome in the absence of complete data.

• A substance's molecular composition is expressed in terms of the number and type of atoms that make up each molecule.

• The "true formula" is another name for the molecular formula.

• A structural formula describes the atom's arrangements with one another while also displaying the chemical bonds.

Key Terms

• Lewis dot structure: Lewis structures are diagrams that show the valence electrons of atoms within a molecule. They are often referred to as Lewis dot structures or electron dot structures. The valence electrons of atoms and molecules, whether they reside as lone pairs or within bonds, can be seen using these Lewis symbols and structures.

• Valence electrons: Valence electrons are the electrons located in the outermost electron shell. Since they are the furthest from the nucleus, the atom holds these electrons the least strongly. They participate in chemical reactions and bonding.

• Isomers: Isomers are compounds that have the same number of atoms as one another, hence they have the same empirical formula, but differing from one another in terms of how the atoms are arranged.

FAQs How are molecular formulas written? A molecule is represented by a molecular formula, which includes subscripts to indicate the number of each type of atom in the molecule after chemical symbols to represent the various types of atoms in the molecule. (A subscript is used when there are many atoms of a specific kind present. What does the chemical symbol imply? The chemical sign represents: (i) The name of the element (ii) one of the element's atoms (iii) the quantity of the element that is equivalent to its atomic mass, or gram atomic mass. What distinguishes a molecular formula from a structural formula? The arrangement of atoms in a molecule and the different types of bonds that connect them are depicted in a structural formula. On the other hand, a molecular formula just specifies the kinds and numbers of atoms that are present in a molecule. For instance, water has the structural formula H-O-H and the molecular formula H₂O. What distinguishes a Lewis structure from a structural formula? The arrangement of atoms in a molecule and the different types of bonds that connect them are depicted in a structural formula. On the other hand, the arrangement of atoms in a molecule as well as the number of valence electrons on each atom is displayed in a Lewis structure. What distinguishes a molecular formula from an empirical formula? The molecular formula provides the total number of atoms of an element present in the compound, and the empirical formula represents the simplest ratio of atoms involved in the compound and shows the proportion of components in a compound.