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Chemical Formulas: Part 1

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Created on January 31, 2025

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Transcript

Chemical Formulas- Part 1
Atoms, Elements, & Compounds
Chemical Formulas
Number of Elements and Atoms in a Compound

To determine the number of elements in a compound using a chemical formula: 1. Identify each unique element symbol in the formula. 2. Count the different symbols—each represents a distinct element. Example: Na2SO4 has three elements— Sodium (Na), Sulfur (S), and oxygen (O).

To count atoms in a compound using a chemical formula: 1. Identify each element in the formula. 2. Read the subscripts – they indicate how many atoms of each element are present. -If no subscript is shown, it means 1 atom. 3. Add up all the atoms to find the total number in the compound.

2 Sodium (Na) atoms 1 Sulfur (S) atom + 4 Oxygen (O) atoms

Na2SO4

Sodium Sulfate

7 atoms total in each formula unit of Na2SO4

Compounds are substances made of atoms from two or more different elements chemically combined in a fixed ratio.

Elements are types of atoms, represented by symbols on the periodic table (e.g., H for hydrogen, Ag for silver, O for oxygen). Symbols always start with a capital letter, with a lowercase second letter if present.

Atoms are the smallest units of matter that make up everything.

Covalently bonded compounds, such as water (H2O), are called molecules. These molecules exist as individual units.

Ag

Ionic compounds, such as salt (NaCl), are made of formula units, which are the smallest repeating units in their crystal lattice.

Atoms are often represented as circles in diagrams.

There are 118 known elements (kinds of atoms).

A chemical formula is a mathematical model that displays the number of atoms of each element that form a chemical compound.

How to Read a Chemical Formula:

  • Element Symbols – Each element is represented by one or two letters, such as C for carbon and Ca for calcium.
  • Subscripts – A small number after an element shows how many atoms of that element are in each formula unit. If no subscript is written, it means one atom.

Chemical Formula for Calcium Carbonate

Ca

Ca represents calcium. Since there is no subscript, one formula unit of calcium carbonate (CaCO₃) contains one calcium atom.

CaCO3

The subscript "3" means there are 3 oxygen (O) atoms in one formula unit of calcium carbonate (CaCO3).

C represents carbon. Since there is no subscript, one formula unit of calcium carbonate (CaCO3) has one carbon atom.