function calculateAverageAtomicMass() {
var isotope1Mass = parseFloat(document.getElementById('isotope1Mass').value);
var isotope1Abundance = parseFloat(document.getElementById('isotope1Abundance').value);
var isotope2Mass = parseFloat(document.getElementById('isotope2Mass').value);
var isotope2Abundance = parseFloat(document.getElementById('isotope2Abundance').value);
var isotope3Mass = parseFloat(document.getElementById('isotope3Mass').value);
var isotope3Abundance = parseFloat(document.getElementById('isotope3Abundance').value);
var totalWeightedMass = 0;
var totalAbundance = 0;
var isValid = true;
var resultDiv = document.getElementById('averageAtomicMassResult');
resultDiv.innerHTML = "; // Clear previous results
// Process Isotope 1
if (!isNaN(isotope1Mass) && !isNaN(isotope1Abundance) && isotope1Abundance >= 0) {
totalWeightedMass += isotope1Mass * (isotope1Abundance / 100);
totalAbundance += isotope1Abundance;
} else if (!isNaN(isotope1Mass) || !isNaN(isotope1Abundance)) {
isValid = false;
resultDiv.innerHTML = 'Please enter valid numbers for Isotope 1 Mass and Abundance.';
}
// Process Isotope 2
if (!isNaN(isotope2Mass) && !isNaN(isotope2Abundance) && isotope2Abundance >= 0) {
totalWeightedMass += isotope2Mass * (isotope2Abundance / 100);
totalAbundance += isotope2Abundance;
} else if (!isNaN(isotope2Mass) || !isNaN(isotope2Abundance)) {
isValid = false;
resultDiv.innerHTML = 'Please enter valid numbers for Isotope 2 Mass and Abundance.';
}
// Process Isotope 3 (Optional)
if (!isNaN(isotope3Mass) && !isNaN(isotope3Abundance) && isotope3Abundance >= 0) {
totalWeightedMass += isotope3Mass * (isotope3Abundance / 100);
totalAbundance += isotope3Abundance;
} else if ((!isNaN(isotope3Mass) && isNaN(isotope3Abundance)) || (isNaN(isotope3Mass) && !isNaN(isotope3Abundance))) {
isValid = false;
resultDiv.innerHTML = 'Please ensure both Isotope 3 Mass and Abundance are entered if using this field.';
}
if (!isValid) {
return;
}
if (totalAbundance === 0) {
resultDiv.innerHTML = 'Please enter at least one isotope\'s mass and abundance.';
return;
}
var averageAtomicMass = totalWeightedMass; // No division by totalAbundance if abundances are percentages
resultDiv.innerHTML += '
';
if (Math.abs(totalAbundance – 100) > 0.01 && totalAbundance > 0) { // Allow for slight floating point inaccuracies
resultDiv.innerHTML += '
';
}
}
.average-atomic-mass-calculator-container {
font-family: 'Arial', sans-serif;
background-color: #f9f9f9;
border: 1px solid #ddd;
padding: 20px;
border-radius: 8px;
max-width: 600px;
margin: 20px auto;
box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}
.average-atomic-mass-calculator-container h2 {
color: #333;
text-align: center;
margin-bottom: 20px;
}
.average-atomic-mass-calculator-container p {
color: #555;
line-height: 1.6;
}
.calculator-input-group {
background-color: #fff;
border: 1px solid #eee;
padding: 15px;
border-radius: 5px;
margin-bottom: 15px;
}
.calculator-input-group h3 {
color: #0056b3;
margin-top: 0;
margin-bottom: 10px;
border-bottom: 1px solid #eee;
padding-bottom: 5px;
}
.calculator-input-group label {
display: block;
margin-bottom: 5px;
color: #333;
font-weight: bold;
}
.calculator-input-group input[type="number"] {
width: calc(100% – 22px);
padding: 10px;
margin-bottom: 15px;
border: 1px solid #ccc;
border-radius: 4px;
box-sizing: border-box;
}
.average-atomic-mass-calculator-container button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 20px;
}
.average-atomic-mass-calculator-container button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
background-color: #e9f7ef;
border: 1px solid #d4edda;
border-radius: 5px;
text-align: center;
font-size: 1.1em;
color: #155724;
font-weight: bold;
}
.calculator-result p {
margin: 5px 0;
}
Understanding Average Atomic Mass: A Comprehensive Guide
The atomic mass listed on the periodic table for each element isn't a simple whole number. Instead, it's a weighted average of the masses of all the naturally occurring isotopes of that element. This value, known as the average atomic mass, reflects the relative abundance of each isotope found in nature.
What are Isotopes?
Atoms of the same element always have the same number of protons. However, they can have different numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes. Because neutrons contribute significantly to an atom's mass, isotopes of the same element have different masses. For example, carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons, making carbon-14 heavier.
Why is Average Atomic Mass Important?
When you work with a sample of an element in a laboratory, you're not dealing with just one type of isotope. You're dealing with a mixture of all its naturally occurring isotopes, each present in a specific proportion. The average atomic mass allows chemists to use a single, representative mass for calculations involving that element, simplifying stoichiometry and other chemical computations.
The Formula for Average Atomic Mass
Calculating the average atomic mass involves a simple, yet crucial, weighted average formula:
Average Atomic Mass = (Isotope₁ Mass × Isotope₁ Abundance) + (Isotope₂ Mass × Isotope₂ Abundance) + ...
Where:
- Isotope Mass: The exact atomic mass of a specific isotope, usually measured in atomic mass units (amu).
- Isotope Abundance: The natural abundance of that isotope, expressed as a decimal (e.g., 75% becomes 0.75) or as a percentage (e.g., 75.77%). If using percentages, the sum of the products will directly give the average atomic mass.
It's critical that the sum of the natural abundances for all isotopes of an element equals 100% (or 1.0 if using decimals).
Step-by-Step Example: Calculating the Average Atomic Mass of Chlorine
Let's use the element Chlorine (Cl) as an example. Chlorine has two major naturally occurring isotopes:
- Chlorine-35: Isotopic Mass = 34.96885 amu, Natural Abundance = 75.77%
- Chlorine-37: Isotopic Mass = 36.96590 amu, Natural Abundance = 24.23%
Now, let's apply the formula:
- Convert abundances to decimals (if necessary, or use percentages directly):
- Chlorine-35 abundance: 75.77% = 0.7577
- Chlorine-37 abundance: 24.23% = 0.2423
- Multiply each isotope's mass by its decimal abundance:
- For Chlorine-35: 34.96885 amu × 0.7577 = 26.4959 amu
- For Chlorine-37: 36.96590 amu × 0.2423 = 8.9568 amu
- Sum the results:
- Average Atomic Mass = 26.4959 amu + 8.9568 amu = 35.4527 amu
Therefore, the average atomic mass of Chlorine is approximately 35.4527 amu, which matches the value found on the periodic table.
Using the Calculator
Our Average Atomic Mass Calculator simplifies this process. Simply input the isotopic mass and its corresponding natural abundance (as a percentage) for each isotope. The calculator will then perform the weighted average calculation for you, providing the average atomic mass in atomic mass units (amu).
Remember to ensure that the sum of the abundances you enter for all isotopes is close to 100% for the most accurate representation of the element's average atomic mass.