Atoms and Moles – Chapter 3

Substances are made of atoms 3.1

Atomic Theory

Atomic Theory – Atoms are the building blocks of all matter.

Research into this theory led to three laws that all compounds share…

What does an atom look like?

Law of Definite Proportions

A given compound contains the same elements in exactly the same proportions by mass, regardless of the size of the sample or the source of the compound.

Law of Definite Proportions

Sodium chloride is an example. All samples of pure NaCl will be 39.34% Na by mass and 60.66% Cl by mass no matter where the NaCl comes from.

Sodium Chloride

Chlorine

Sodium

Law of Conservation of Mass

The mass of the products of a reaction equals the mass of the reactants.

Applies when elements combine to produce a compound, decompose, or when atoms in a compound rearrange.

Law of Conservation of Mass

+

32.07 +32.00 64.07

amu amu amu

S OOOO

S

E=mc²When you combine sulfur and

oxygen, 296,800 J of energy are given off as heat.

According to E=mc²…

296,800kg•m²/s² = m(2.998 x 108m/s)²

Rearranging this equation gives the mass to be 3.302 x 10-12 kg

Where does this mass go?

The Law of Multiple Proportions

States that the mass ratio for one of the elements in a compound that combines with a fixed mass of another element can be expressed in small whole numbers.

Dalton’s Atomic Theory

Dalton used the three laws.Elements and compounds

differ b/c of the types of atoms.

Properties differ because of atoms.

His Theory

Dalton proposed 5 principles that make up his theory on the atomic structure of matter.

Dalton’s Five Principles

1. All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed.

2. Atoms of a given element are identical in their physical and chemical properties.

Dalton’s Five Principles

3. Atoms of different elements differ in their physical and chemical properties.

4. Atoms of different elements combine in simple whole-number ratios to form compounds.

Dalton’s Last Principle

5. In chemical reactions atoms are combined, separated, or rearranged, but never created, destroyed, or changed.

Are they still true?

At the time, this explained the chemical data that they had.

Two invalid principles.Is it still a theory?

Concept Check

According to Dalton, what is the difference between an element and a compound?

What are the five principles of Dalton’s atomic theory?

Atomic Mass

Atomic Mass – the mass of an atom in atomic mass units (amu)

AveragesAtoms of an element have

different masses.AKA: the Dalton (Da)The mass of C is 12.011 amu

The mole!

The mole is the SI unit for amount.

Why the mole?

6.023 x 1023

THE MOLE!

Based on an isotope of carbon.

A mole is exactly the number of atoms in 12 grams of the carbon-12 atom.

Mole

1 mole of atoms of any element has a mass in grams that is equal to the atoms mass in amu’s.

18.9984 amu of F = 18.9984 g/mol of F

Avogadro's Number

6.022 x 1023 is Avogadro’s #.It’s the # of particles in 1 mole.If 6 billion people were to count the

atoms in 1 mole, it would take them over 3 million years to count them all if counting at the rate of 1 atom/second.

Section Review

Complete the section review on page 81. Do problems 1-7.