The The Structure Structure

of the of the AtomAtom

Important contributors to the Atomic Important contributors to the Atomic TheoryTheory

DemocritusDemocritus DaltonDalton RutherfordRutherford

AristotleAristotle J. J. ThomsonJ. J. Thomson BohrBohr

The Atom: Early TheoriesThe Atom: Early Theories Democritus versus Dalton similarities

– Both believedMatter composed of extremely small particles

called atomsAll atoms of a given element are identical, but

different from the atoms of other elementsAtoms could not be created, divided, or destroyedApparent changes in matter result from changes in

the groupings of atoms

The Atomic Theory: Democritus and The Atomic Theory: Democritus and Dalton differencesDalton differences

– DemocritusMatter is composed of empty space through

which atoms moveDifferent kinds of atoms come in different

sizes and shapesThe differing properties of atoms are due to

the size, shape, and movement of atoms– DaltonDalton

Different atoms combine in simple whole number ratios to form compounds

Dalton’s Atomic TheoryDalton’s Atomic Theory

The Atom: Subatomic particles and the The Atom: Subatomic particles and the nuclear atomnuclear atom

How were the various parts of the atom discovered?– Electrons were discovered by the experiments

of many scientists using cathode rays.JJ Thomson was able to determine the ratio

of the electron’s charge to its massRobert Millikan determined the charge of

the electron and was able to calculate the mass of a single electron

http://www.learnerstv.com/animation/animation.php?ani=186&cat=chemistry

J. J. Thomson: Plum Pudding ModelJ. J. Thomson: Plum Pudding Model

Discovery of subatomic particlesDiscovery of subatomic particles

– The nucleus was discovered by Ernest Rutherford and his gold foil experiment http://www.youtube.com/watch?v=5pZj0u_XMbc

Rutherford refined his definition to include the proton

Rutherford and James Chadwick discovered the neutron

The atomThe atomBohrBohr-- e- only have “allowable E states” e- around nucleus in orbits

Particle Symbol Location Relative charge

Relative mass

Actual mass (g)

electron e- electron cloud 1- 1/1840 9.11 x 10-28

proton p+ nucleus 1+ 1 1.673 x 10-24

neutron n0 nucleus 0 1 1.675 x 10-24

The Atom: How Atoms DifferThe Atom: How Atoms DifferChemical nameAtomic numberChemical SymbolAverage Atomic Mass

Atomic number = number of protons = number of electrons How many protons and electrons are in each of the following

atoms?– boron– radon– platinum– magnesium

An atom of an element contains 66 electrons. What element is it?

An atom contains 14 protons. What element is it?

Hydrogen1H

1.00794

LET’S REVIEW…LET’S REVIEW…1. Which scientist came up with the plum

pudding model? 2. Why was it called this?3. Who discovered the nucleus of the atom?4. What was wrong with Dalton’s atomic

theory?5. How many protons, neutrons, and

electrons are in each of the following atoms?a) boronb) radon

Let’s Review: AnswersLet’s Review: Answers1. Which scientist came up with the plum

pudding model? J. J. Thomson J. J. Thomson 2. Why was it called this?3. Who discovered the nucleus of the atom?

RutherfordRutherford4. What was wrong with Dalton’s atomic theory?

He stated that the atom was He stated that the atom was “indivisible”“indivisible”

5. How many protons, neutrons, and electrons are in each of the following atoms?a) Boron: p p++, e, e-- = 5, n = 5, noo= 6= 6b) Radon: pp++, e, e-- = 86, n = 86, noo= 136= 136

The Atom: How Atoms Differ contThe Atom: How Atoms Differ cont

Isotopes– An element with a different amount of neutrons in its nucleus– PROTON determines the ID– Representing isotopes:

How atoms differHow atoms differ– Element – mass #

– carbon – 12, carbon – 13, carbon – 14– The mass number represents the total protons and neutrons in

an element– How many protons, electrons, and neutrons in the following

isotopes? Name each isotope and write its symbol.

Atomic Structure: IsotopesAtomic Structure: Isotopes Atomic masses of elements on the table are based on

naturally occurring isotopes Weighted scale – abundance(mass)

Average atomic mass = Average atomic mass =

(mass 1 x rel. abundance 1) + (mass 2 x rel. abundance 2)(mass 1 x rel. abundance 1) + (mass 2 x rel. abundance 2) Element C has two naturally occurring isotopes. The

isotope with mass number 10 has a relative abundance of 20%. The isotope with mass number 11 has a relative abundance of 80%.

Use these figures to estimate the average atomic mass for element C. State the atomic number and the true value of element C

Atomic Structure: IsotopesAtomic Structure: Isotopes– Complete the following table

Isotope Atomic # Mass # p+ e- n0 symbol

20 46

8 17

Ag

hydrogen-3

107

47

Types of Radiation– Alpha Radiation: radiation that is deflected

toward the negatively charged plate. Each alpha particle contains two protons and two neutrons.

– Beta Radiation: radiation that was deflected toward the positively charged plate. Each beta particle is an electron.

– Gamma Radiation: high energy radiation that possesses no mass

88226

86222

24Ra Rn He

614

714

1C N o

92238

90234

24

002Ra Th He

The Atom ReviewThe Atom Review Atomic theories

– Democritus vs. Dalton Subatomic particles and the atom

– JJ Thompson – determined the charge to mass ratio of the electron

– Robert Millikan – determined the charge and mass of the electron

– Rutherford – discovered the nucleus and later the proton– Rutherford and James Chadwick – discovered the neutron

Atomic Number Isotopes Average Atomic Mass Types of Radiation