Atomic Models

Around 400 BC a Greek scientist called Democritus said that matter was made up of small particles he named 'Atoma' (meaning indivisible).

Dalton - 1803 - round ball with a positive nucleusElement made up of atoms that cannot be divided Atoms of the same element are alikeAtoms of different elements can join in whole number ratios to form molecules

Thompson - discovered electrons in 1897

Based on his alpha-particlescattering experiment on gold, Rutherford concludedthat the atom consisted ofa hard central core wheremost of the mass of theatom rested.

Rutherford - discovered the nucleus 1911

http://www.learnerstv.com/animation/animation.php?ani=121&cat=chemistry

Bohr - electrons travel in paths (energy levels) around the nucleus - 1913

http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-atoms.shtml

Protons

PositiveMass = 1 amu = 1.67 x 10-24 gDiscovered by E. Goldstein in 1886Symbol – p+Electrons

Negative chargedMass = 1/1840 amu = 9.11 x10-28Discovered by J.J. Thompson in 1897 Symbol – e-1

Neutrons

NeutralMass = 1 amu = 1.67 x 10-24gDiscovered by James Chadwick in 1932Symbol - no

The Atomic Nucleus

Small DensePositive chargeCore of an atomContains protons and neutronsDiscovered by Ernest Rutherford in 1911

P+No

Valence electron - an electron in the outermost energy level of an atom

Chadwick - discovered the neutrons in 1932

Modern Theory - electrons do not move in definite paths but the exact position, speeds and direction of electrons cannot be determined.

Modern - electron cloud theory replaced Bohr’s model in 1925 http://

intro.chem.okstate.edu/1314F97/Chapter6/BohrQuantum.html

e- enter lowest energy level first

p orbitals can hold a maximum of two electrons so all three together can hold a total of 6 electrons

As s orbital is shaped lie a sphere, so it has only one possible orientation in space. An s orbital can hold a maximum of two valence electrons

http://micro.magnet.fsu.edu/electromag/java/atomicorbitals/index.html

The Atom

2 protons = +22 neutrons = 02 electrons = -2Net charge = 0

Atomic NumberAtoms are composed of protons, neutrons and electronsElectrons surround the nucleus and occupies most of the volume of the atomThe number of protons in the nucleus of an atomEach element has a different number of protons; therefore, a different atomic numberNumber of protons = number of electronsTherefore the atom is neutral

P+no

e-

e-

e-

e-

The Atom – mostly empty space

Mass Number

Most of the mass of an atom is in the nucleusProtons = 1 amuNeutrons = 1 amuElectron = 1/1840 amuMass Number = Protons + NeutronsNeutrons = Mass number - Protons

12

C 6

Mass Number

Symbol

Atomic Number = p+

Neutrons = Mass Number - Atomic Number

3.2.9

Isotopes

IsotopesSame number of protons and electronsDifferent number of neutronsTherefore – Different mass numbers

10p+11no

10p+10no

10p+12no

20

Ne10

22

Ne10

21

Ne10

Atomic Mass

Atomic mass = weighted average of the masses of its isotopesYou calculate the atomic mass based on relative abundanceExample: Copper atomic mass= 63.546Isotopes – Cu-63 and CU-65Isotope Cu-63 more abundant

Y-10 20%

Y-21 80%

mass X % = Relative Weight10 X .20 = 221 X .80 =16.8 Total = 18.8 amu

MASS Weigh Add

Number Count Add

Average Mass

Mass/ Number

Don't do

% Part/Whole X100

Should equal 100

Relative abundance

Divide % by 100

Should equal 1

Relative Weight

Relative Abundance X Average Mass

Add

Kidney Brown Mac Total

http://www.quia.com/cb/147081.html

Atomic Structure Jeopardy

http://www.quia.com/hm/110454.html

Hangman

http://www.quia.com/rr/70834.html