chapter 3 atoms: the building blocks of matter the atom: from philosophical idea to theory 3.1 the...

ChapterChapter 33Atoms: Atoms: The Building The Building Blocks of Matter Blocks of Matter

The Atom: From Philosophical Idea to Theory

3.1 The Atom: From Philosophical Idea to Theory

Democritus (400 BC)"The only existing things

are atoms and empty

space; all else is opinion”

Coined the term “atomos”

Law of Conservation of MassLaw of Conservation of Mass

Total mass of reactants

= Total mass of productsAntoine Lavoisier

Mass is neither created nor destroyed during chemical or physical reactions.

Law of Definite Proportions

• A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the sample

Law of Multiple Proportions • If two or more different compounds are

composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

a. CO2 and CO

b. H2O and H2O2

Dalton’s Atomic Theory (1808)Dalton’s Atomic Theory (1808)

All matter is composed of extremely

small particles called atoms

Atoms of a given element are

identical in size, mass, and other

properties; atoms of different elements

differ in size, mass, and other properties

John Dalton

Dalton’s Atomic Theory (1808)Dalton’s Atomic Theory (1808)

Atoms cannot be subdivided, created,

or destroyed

Atoms of different elements combine in

simple whole-number ratios to form

chemical compounds

In chemical reactions, atoms are

combined, separated, or rearranged

John Dalton

Modern Atomic TheoryModern Atomic TheorySeveral changes have been made to Dalton’s theory.

Dalton said:

Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties

Modern theory states:

Atoms of an element have a characteristic average mass which is unique to that element.



3.2 The Structure of the Atom

IsotopesIsotopes

Elements occur in nature as mixtures of isotopes.

Isotopes are atoms of the same element that differ in the number of neutrons

Atomic MassesAtomic Masses

Isotope Symbol Composition of the nucleus

% in nature

Carbon-12 12C 6 protons

6 neutrons

98.89%


7 neutrons

1.11%


8 neutrons

<0.01%

Atomic mass is the average of all the naturally occurring isotopes of that element.Carbon = 12.011

1 amu (atomic mass unit) = 1/12 the mass of a carbon-12 1 amu (atomic mass unit) = 1/12 the mass of a carbon-12 atom; also = 1.660540 x 10atom; also = 1.660540 x 10-27-27 kg kg

Modern Atomic Theory #2Modern Atomic Theory #2Dalton said:

Modern theory states:

Atoms cannot be subdivided, created, or destroyed

Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!

Discovery of the ElectronDiscovery of the ElectronIn 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

Some ModernSome ModernCCathode athode RRay ay TTubesubes

Thomson’s Atomic ModelThomson’s Atomic Model

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Mass of the ElectronMass of the Electron1909 – Robert Millikan determines the mass of the electron.

The oil drop apparatus

Mass of the electron is 9.109 x 10-31 kg

Conclusions from the Study Conclusions from the Study of the Electronof the Electron

Cathode rays have identical properties regardless of the

element used to produce them. All elements must contain

identically charged electrons.

Atoms are neutral, so there must be positive particles in

the atom to balance the negative charge of the electrons

Electrons have so little mass that atoms must contain

other particles that account for most of the mass

Rutherford’s Gold Foil Rutherford’s Gold Foil ExperimentExperiment

Alpha particles are helium nuclei Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recorded

Try it Yourself!Try it Yourself!In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

The AnswersThe AnswersTarget #1

Target #2

Rutherford’s FindingsRutherford’s Findings

The nucleus is small The nucleus is dense The nucleus is positively charged

Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected

“Like howitzer shells bouncing off of tissue paper!”

Conclusions: Cool Website!

http://micro.magnet.fsu.edu/electromag/java/rutherford/

Atomic ParticlesAtomic ParticlesParticle Charge Mass (kg) Location

Electron -1 9.109 x 10-31 Electron cloud

Proton +1 1.673 x 10-27 Nucleus

Neutron 0 1.675 x 10-27 Nucleus

The Atomic The Atomic ScaleScale

Most of the mass of the

atom is in the nucleus

(protons and neutrons)

Electrons are found outside

of the nucleus (the electron

cloud)

Most of the volume of the

atom is empty space

“q” is a particle called a “quark”



3.3Counting Atoms

Atomic NumberAtomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

Element # of protons Atomic # (Z)

Carbon 6 6

Phosphorus 15 15

Gold 79 79

Isotopes…Again (must be on the test)Isotopes…Again (must be on the test)Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.

Isotope Protons Electrons Neutrons Nucleus

Hydrogen–1

(protium)

1 1 0

Hydrogen-2

(deuterium)

1 1 1

Hydrogen-3

(tritium)

1 1 2

Mass NumberMass Number

Mass number is the number of protons and neutrons in the nucleus of an isotope.

Mass # = p+ + n0

Nuclide p+ n0 e- Mass #

Oxygen - 10

- 33 42

- 31 15

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

Practice1. How many protons, neutrons & electrons make

up an atom of carbon-13?

2. Write the nuclear symbol for oxygen-16.

3. Write the hyphen notation for the element whose atoms have 7 electrons & 9 neutrons.

6 protons, 6 electrons & 7 6 protons, 6 electrons & 7 neutrons neutrons

Nitrogen-16Nitrogen-16

The Mole• In chemistry, we use a new unit to In chemistry, we use a new unit to

quantify an amount of a substance. quantify an amount of a substance. • This unit is called the This unit is called the molemole; ;

abbreviated mol. abbreviated mol. (no, not an animal or a dermatological (no, not an animal or a dermatological spot)spot)

• The same way the supermarket uses a The same way the supermarket uses a dozen to quantify 12 objects, we use a dozen to quantify 12 objects, we use a mole to quantify mole to quantify

6.02 x 106.02 x 102323 objects. objects. • This unit helps chemists determine the This unit helps chemists determine the

number of particles in a sample of number of particles in a sample of matter without counting them. matter without counting them.

The MoleThe Mole

1 dozen =

1 gross =

1 ream =

1 mole =

12

144

500

6.02 x 1023

There are exactly 12 grams of carbon-12 in one mole of carbon-12.

Avogadro’s NumberAvogadro’s Number6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro (1776-1855).

Amadeo Avogadro

I didn’t discover it. Its just named after me!

Calculations with Moles:Calculations with Moles:Converting moles to gramsConverting moles to grams

How many grams of lithium are in 3.50 moles of lithium?

3.50 mol Li= g Li

1 mol Li

6.94 g Li24.3X

Calculations with Moles:Calculations with Moles:Converting grams to molesConverting grams to moles

How many moles of lithium are in 18.2 grams of lithium?

18.2 g Li = mol Li6.94 g Li

1 mol Li2.62X

Calculations with Moles:Calculations with Moles:Using Avogadro’s NumberUsing Avogadro’s Number

How many atoms of lithium are in 3.50 moles of lithium?

3.50 mol Li = atoms Li

1 mol Li

6.022 x 1023 atoms Li2.11 x 1024X

Calculations with Moles:Calculations with Moles:Using Avogadro’s NumberUsing Avogadro’s Number

How many atoms of lithium are in 18.2 g of lithium?

18.2 g Li

= atoms Li

1 mol Li 6.022 x 1023 atoms Li

1.58 x 1024

6.94 g Li 1 mol Li

(18.2)(6.022 x 1023)/6.94

X X

More Practice1. What is the mass is grams of 3.6 mol of carbon?

2. What is the mass in grams of 1.733 mol of sulfur?

3. How many moles of copper are in 3.22 g copper?

4. How many moles of lithium are in 2.72 x 10-4 g

lithium?

5. How many moles of carbon are in 2.25 x 1022 atoms

of carbon?

43 g43 g

23.5 g23.5 g

0.0507 mol0.0507 mol

3.92 x 103.92 x 10-5-5 mol mol

0.0374 mol0.0374 mol

Even More Practice!6. How many moles of oxygen, O, are in 2,000,000

atoms oxygen?

7. How many atoms of sodium are in 3.80 mol sodium?

8. What is the mass in grams of 5.0 x 109 atoms of neon?

9. How many atoms of carbon are in 0.020 g carbon?

10. What mass of silver contains the same number of atoms as 10.0 g of boron?

1.0 x 101.0 x 102121 atoms atoms

1.7 x 101.7 x 10-13-13 g g

99.8 g99.8 g

3 x 103 x 10-18-18 mol mol

2.29 x 102.29 x 102424 atoms atoms

chapter 3 atoms: the building blocks of matter the atom: from philosophical idea to theory 3.1 the...

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