Chemists use the mole to count atoms, molecules, ions, and formula units. Section 1: Measuring Matter K What I Know W What I Want to Find Out L What I Learned

8(A) Define and use the concept of a mole. 8(B) Use the mole concept to calculate the number of atoms, ions, or molecules in a sample of material. 2(G) Express and manipulate chemical quantities using scientific conventions and mathematical procedures, including dimensional analysis, scientific notation, and significant figures. Measuring Matter Copyright © McGraw-Hill Education

Essential Questions How is a mole used to indirectly count the number of particles of matter? What is a common everyday counting unit to which the mole can be related? How can moles be converted to number of representative particles and vice versa? Measuring Matter Copyright © McGraw-Hill Education

Review Molecule: forms when two or more atoms covalently bond and is lower in potential energy than its constituent atoms Atomic mass: the weighted average mass of the isotopes of that element Atomic mass Unit (amu): one twelfth the mass of a carbon-12 atom New Mole: the SI Unit used to measure the amount of a substance Ex. The number of carbon atoms in exactly 12 g of pure carbon Amount 6.02 x Avogadro’s number: 6.02 X Measuring Matter Copyright © McGraw-Hill Education Vocabulary

Practice Review Write the following in scientific notation – – 24,367 – 400 Circle the significant figures in the number below – 75,600,000 – – 3.140

Counting Particles Chemists need a convenient method for accurately counting the number of atoms, molecules, or formula units of a substance. The mole is the SI base unit used to measure the amount of a substance. 1 mole is the amount of atoms in 12 g of pure carbon-12, or 6.02 ×10 23 representative particles, which is any kind of particle – an atom, a molecule, a formula unit, an electron, an ion, etc. The number is called Avogadro’s number. Measuring Matter Copyright © McGraw-Hill Education Mole- SI based unit used to measure the quantity of matter

Avogadro's Number

List common counting units and their values Dozen – Pair- Gross- Ream -

Why the need for a new counting number A convenient method for accurately counting atoms, molecules, or formula units in a sample of a substance. Atoms are so small and there are so many of them that it is impossible to count them directly.

What can be measured using a mole atom Molecule Formula unit

Converting Between Moles and Particles Conversion factors must be used. Moles to particles: Number of molecules in 3.50 mol of sucrose: Measuring Matter Copyright © McGraw-Hill Education

Converting Between Moles and Particles Particles to moles Use the inverse of Avogadro’s number as the conversion factor. Measuring Matter Copyright © McGraw-Hill Education

Measuring Matter Copyright © McGraw-Hill Education PARTICLES-TO-MOLES CONVERSION Use with Example Problem 1. Problem Zinc (Zn) is used as a corrosion-resistant coating on iron and steel. It is also an essential trace element in your diet. Calculate the number of moles of zinc that contain 4.50 × atoms. Response ANALYZE THE PROBLEM You are given the number of atoms of zinc and must find the equivalent number of moles. If you compare 4.50 × atoms Zn with 6.02 × 10 23, the number of atoms in 1 mol, you can predict that the answer should be less than 10 mol. KNOWN Number of atoms = 4.50 × atoms Zn 1 mol Zn = 6.02 × atoms Zn UNKNOWN Moles Zn = ? mol

Measuring Matter Copyright © McGraw-Hill Education PARTICLES-TO-MOLES CONVERSION EVALUATE THE ANSWER Both the number of Zn atoms and Avogadro’s number have three significant figures. Therefore, the answer is expressed correctly with three digits. The answer is less than 10 mol, as predicted, and has the correct unit, moles.

Conversion Practice Calculate the number of molecules in 11.5 mol of water.

Conversion Practice Silver Nitrate is used to make several different silver halides used in photographic films. How many formula units of silver nitrate are there in 3.25 mol of silver nitrate?

Measuring Matter Copyright © McGraw-Hill Education Review Essential Questions How is a mole used to indirectly count the number of particles of matter? What is a common everyday counting unit to which the mole can be related? How can moles be converted to number of representative particles and vice versa? Vocabulary mole Avogadro’s number