ATOMICATOMIC

THEORYTHEORY

Defining the AtomDefining the Atom

An atom is the An atom is the smallestsmallest particle particle of an element that retains its of an element that retains its identity in a reaction.identity in a reaction.

The basic building blocks of The basic building blocks of matter that make-up everyday matter that make-up everyday objects.objects.

DemoCritusDemoCritus

Early Greek Scholar-was the first to Early Greek Scholar-was the first to suggest the existence of atomssuggest the existence of atoms

He believed that atoms were He believed that atoms were indivisible and indestructible.indivisible and indestructible.

Never developed a theory Never developed a theory lacked experimental supportlacked experimental support

Dalton’s Atomic TheoryDalton’s Atomic Theory

Put Democritus’s ideas into a scientific theory.Put Democritus’s ideas into a scientific theory. 1) All matter is composed of tiny indivisible 1) All matter is composed of tiny indivisible

particles called atoms.particles called atoms. 2) Atoms of the same element are identical.2) Atoms of the same element are identical. 3) Atoms of different elements can mix 3) Atoms of different elements can mix

together to form compoundstogether to form compounds 4) Chemical reactions occur when atoms are 4) Chemical reactions occur when atoms are

separated, joined, or rearranged.separated, joined, or rearranged.

Dalton’s Theory RevisedDalton’s Theory Revised

Most of Dalton’s theory is still Most of Dalton’s theory is still accepted today EXCEPT that accepted today EXCEPT that atoms are known to be divisible.atoms are known to be divisible.

Atoms can be broken down into Atoms can be broken down into 3 subatomic particles: electrons, 3 subatomic particles: electrons, protons and neutrons.protons and neutrons.

J.J. ThomsonJ.J. Thomson

Used a cathode Used a cathode ray tube to prove ray tube to prove the smallest the smallest particles present particles present must have a must have a negative charge.negative charge.

He discovered He discovered the ELECTRON!the ELECTRON!

http://www.youtube.com/watch?v=RW_zfKOU9uM&feature=related

J.J. ThomsonJ.J. Thomson

Atoms were electrically Atoms were electrically neutral, so there must neutral, so there must be a + particle to cancel be a + particle to cancel out the – charge from out the – charge from the electron.the electron.

Developed the Plum Developed the Plum Pudding Model (positive Pudding Model (positive ball containing scattered ball containing scattered electrons)electrons)

Ernest RutherfordErnest Rutherford

Former student of Former student of Thomson, disproved the Thomson, disproved the Plum Pudding Model of the Plum Pudding Model of the atom.atom.

The Gold Foil Experiment: The Gold Foil Experiment: Sent a beam of + charges Sent a beam of + charges (alpha particles) through a (alpha particles) through a piece of very thin gold foil.piece of very thin gold foil.

Angles of deflection were Angles of deflection were measured.measured.

RutherfordRutherford

Results: Most of the alpha particles passed Results: Most of the alpha particles passed straight through, most of the foil must be straight through, most of the foil must be regions of “empty” space – not a + sphere regions of “empty” space – not a + sphere like Thomson believed.like Thomson believed.

+ charges and the atoms mass must be + charges and the atoms mass must be found in the center found in the center discovered the discovered the nucleusnucleus

The Nuclear AtomThe Nuclear Atom

In Rutherford’s atomic model, the In Rutherford’s atomic model, the protons and neutrons are located protons and neutrons are located in the nucleus. in the nucleus.

The electrons are distributed The electrons are distributed around the nucleus and occupy around the nucleus and occupy almost all the volume of the atoms.almost all the volume of the atoms.

ATOMIC STRUCTUREATOMIC STRUCTURE

Particle

proton

neutron

electron

Charge

+ ve charge

-ve charge

No charge

1

1

nil

Mass

ATOMIC STRUCTUREATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

HeHe22

44 Atomic mass

Atomic number

number of electrons = number of protons

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

Are atoms electrically neutral? Why?

Complete the following table in your Complete the following table in your notesnotes

Atomic #Atomic # Mass #Mass # # of # of ProtonsProtons

# of # of NeutronsNeutrons

# of # of ElectronsElectrons

99 1010

1414 1515

4747 2222

5555 2525

IsotopesIsotopes

Atoms that have the same number of protons but Atoms that have the same number of protons but different numbers of neutronsdifferent numbers of neutrons

Different mass numbersDifferent mass numbers Chemically alike because they have identical Chemically alike because they have identical

numbers for the characteristic chemical behavior numbers for the characteristic chemical behavior of each elementof each element

Ex: Three known isotopes for HEx: Three known isotopes for H– H: Hydrogen (no neutrons, mass # of 1)H: Hydrogen (no neutrons, mass # of 1)– H-2: Deuterium (one neutron, mass # of 2)H-2: Deuterium (one neutron, mass # of 2)– H-3: Tritium (two neutrons, mass # of 3)H-3: Tritium (two neutrons, mass # of 3)

Calculating Average Atomic Mass of Calculating Average Atomic Mass of IsotopesIsotopes

In nature, isotopes occur in various In nature, isotopes occur in various percentages. The higher the percent the percentages. The higher the percent the more abundant.more abundant.

In order to figure out the average mass of In order to figure out the average mass of each element the percent abundance and each element the percent abundance and mass of each isotope need to be consideredmass of each isotope need to be considered

We can calculate average atomic mass in We can calculate average atomic mass in much the same way as we calculate your much the same way as we calculate your grade in this class…grade in this class…

Calculating Average Atomic Calculating Average Atomic MassMass

1.1. Divide the percent abundances by 100. Divide the percent abundances by 100. (natural occurrence)(natural occurrence)

2.2. Multiply each isotope mass by its natural Multiply each isotope mass by its natural occurrence. (maintain sigfigs)*occurrence. (maintain sigfigs)*

3.3. Add up all the masses (maintain place Add up all the masses (maintain place values)values)

4.4. Include a unit (amu)Include a unit (amu)

What are the different categories What are the different categories that you are graded on in this class?that you are graded on in this class? Classwork: 79ptsClasswork: 79pts Practice: 12ptsPractice: 12pts Final: 14ptsFinal: 14pts What would your semester grade be if you What would your semester grade be if you

received an 81% for classwork, 52% for practice, received an 81% for classwork, 52% for practice, and 73% on your final?and 73% on your final?– 0.81 x 79 = 640.81 x 79 = 64– 0.52 x 12 = 6.20.52 x 12 = 6.2– 0.73 x 14 = 100.73 x 14 = 10– Add all answers together to get % semester gradeAdd all answers together to get % semester grade– 63.2 + 3.5 + 10.1 = 80.2 63.2 + 3.5 + 10.1 = 80.2 80 % (a B)80 % (a B)

Now lets try with an element!Now lets try with an element!

Copper has two isotopes: copper-63 and Copper has two isotopes: copper-63 and copper-65. The relative abundances of copper-65. The relative abundances of these isotopes are 69.2% and 30.8% these isotopes are 69.2% and 30.8% respectively. Calculate the average atomic respectively. Calculate the average atomic mass of copper.mass of copper.0.692 x 63 = 43.60.692 x 63 = 43.6

0.308 x 65 = 20.00.308 x 65 = 20.0

43.6 + 20.0 = 63.643.6 + 20.0 = 63.6

One more example…One more example…

Uranium has three naturally occurring Uranium has three naturally occurring isotopes with the following percent isotopes with the following percent abundances: U-234 (0.0058%), U-235 abundances: U-234 (0.0058%), U-235 (0.71%), and U-238 (99.23%). (0.71%), and U-238 (99.23%). – What do you expect the average atomic mass What do you expect the average atomic mass

to be and why?to be and why?– What is the average atomic mass?What is the average atomic mass?

237.9237.9

SUMMARYSUMMARY

1. The Atomic Number of an atom = number of

protons in the nucleus.

2. The Atomic Mass of an atom = number of

Protons + Neutrons in the nucleus.

3. The number of Protons = Number of Electrons.

4. Electrons orbit the nucleus in shells.

5. Each shell can only carry a set number of electrons.

ATOMIC STRUCTUREATOMIC STRUCTURE

There are two ways to represent the atomic

structure of an element or compound;

1. Electronic Configuration

2. Dot & Cross Diagrams

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

With electronic configuration elements are

represented numerically by the number of

electrons in their shells and number of shells. For

example;

N

Nitrogen

7

14

2 in 1st shell

5 in 2nd shell

configuration = 2 , 5

2 + 5 = 7

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

Write the electronic configuration for the following elements;

Ca O

Cl Si

Na20

40

11

23

8

17

16

35

14

28B

11

5

a) b) c)

d) e) f)

2,8,8,2 2,8,1

2,8,7 2,8,4 2,3

2,6

DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS

With Dot & Cross diagrams elements and

compounds are represented by Dots or Crosses to

show electrons, and circles to show the shells. For

example;

Nitrogen N XX X

X

XX

X

N7

14

DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS

Draw the Dot & Cross diagrams for the following elements;

O Cl8 17

16 35a) b)

O

X

XX

X

X

X

X

X

Cl

X

X

X

X X

X

XX

X

X

X

X

X

X

X

X

X