Moles An Introduction

The MOLE The term “mole” is used to count  Atoms of an element  Molecules of a molecular compound  Formula units of an ionic compound One mole is 6.02x10 23 of anything

Avogadro’s Number Amadeo Avogadro  Italian physics professor  Hypothesized “equal volumes of different gases contain equal numbers of atoms” Scientists later expanded his hypothesis for all matter – a molar mass of any substance has the same number of particles

A Mole is a BIG Number A dozen eggs makes a large omelet A mole of eggs would fill all of Earth’s oceans 30 million times

A Mole is a BIG Number It would take 12 billion chickens laying 12 eggs per day about 12 billion years to lay 1 mole of eggs

How Many in a Mole? So why would we ever use such a big number? A mole is 6.02x10 23 items That is: 602,000, sextillion!

Counting Atoms and Molecules Atoms and molecules are very tiny – it takes a LOT of them to make even a single milliliter!  For example, one milliliter of water would have: 3.34x10 22 atoms of oxygen 6.68x10 22 atoms of hydrogen

 Instead of counting …illions and …illions it’s much easier to count in moles Counting Atoms and Molecules

Elemental Molar Masses For any element, the molar mass is equal to its average atomic mass.  Found on the periodic table  Measured in grams per mole (g/mol)

Diatomic Elements Most elements are listed as single atoms when in the elemental form, but seven of them are not. You need to know which elements are diatomic!  Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine and Iodine!

Diatomic Elements Whenever one of these elements is by itself it will always be in twos!  Example: N 2 is nitrogen gas This does NOT affect these elements when they are in a compound, only when by themselves!

Mole Calculations Use dimensional analysis to solve mole problems. Points to remember:  Always go to moles first!  Write your units at every step!

Example 1 How many moles are in 24.6 g of neon? Neon is g/mol

Example 2 What is the mass of 2.50 moles of hydrogen gas? Hydrogen is diatomic, so it is H 2 Molar mass is g/mol

Example 3 How many atoms are in 3.95 moles of beryllium?

Example 4 How many moles are in 5.15x10 23 atoms of sulfur?

Example 5 What is the mass of 2.00x10 24 atoms iron?

Example 6 How many atoms are in 15.4 g lithium?