Atomic Models

1. 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 nucleus • Element made up of atoms that cannot be divided • Atoms of the same element are alike • Atoms of different elements can join in whole number 
ratios to form molecules

2. Thompson - discovered electrons in 1897 Rutherford - discovered the nucleus 1911 Based on his alpha-particle scattering experiment on gold, Rutherford concluded that the atom consisted of a hard central core where most of the mass of the atom rested. http://www.learnerstv.com/animation/animation.php?ani=121&cat=chemistry

3. http://web.visionlearning.com/
custom/chemistry/animations/
CHE1.3-an-atoms.shtmlhttp://web.visionlearning.com/
custom/chemistry/animations/
CHE1.3-an-atoms.shtml Bohr - electrons 
travel in paths 
(energy levels) 
around the nucleus 
- 1913

4. Protons Positive Mass = 1 amu = 1.67 x 10-24 g Discovered by E. Goldstein in 
1886 Symbol – p+ Electrons Negative charged Mass = 1/1840 amu = 
9.11 x10-28 Discovered by J.J. Thompson in 1897 Symbol – e-1 Neutrons Neutral Mass = 1 amu = 1.67 x 10-24g Discovered by James Chadwick in 1932 Symbol - no

5. The Atomic Nucleus Small Dense Positive charge Core of an atom Contains protons and neutrons Discovered by Ernest Rutherford 
in 1911 P+ No Valence electron - an electron in the 
outermost energy level of an atom

6. 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/Chap
ter6/BohrQuantum.html

7. e- enter lowest energy level first • http://micro.mag
net.fsu.edu/electromag/java/atomic
orbitals/index.ht
ml • 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

8. The Atom 2 protons = +2 2 neutrons = 0 2 electrons = -2 Net charge = 0

9. Atomic Number Atoms are composed of 
protons, neutrons and electrons Electrons surround the nucleus 
and occupies most of the volume 
of the atom The number of protons in the 
nucleus of an atom Each element has a different 
number of protons; therefore, a 
different atomic number Number of protons = number 
of electrons Therefore the atom is neutral The Atom – 
mostly empty 
space e
- e
- P+ no e
- e
-

10. Mass Number Mass Number Most of the mass 
of an atom is in the 
nucleus Protons = 1 amu Neutrons = 1 amu Electron = 1/1840 
amu Mass Number = 
Protons + Neutrons Neutrons = Mass 
number - Protons 12 C 6 Symbol Atomic Number = p+

11. Neutrons = Mass Number - Atomic Number Isotopes 3.2.9

13. Isotopes Same number of protons and electrons Different number of neutrons Therefore – Different mass numbers 10p+ 12no 10p+ 10no 10p+ 11no 22 Ne 10 21 Ne 10 20 Ne 10

14. Atomic Mass Atomic mass = weighted average of the 
masses of its isotopes You calculate the atomic mass based on 
relative abundance Example: Copper atomic mass= 63.546 Isotopes – Cu-63 and CU-65 Isotope Cu-63 more abundant Y-10 20% Y-21 80% mass X % = Relative Weight 10 X .20 = 2 21 X .80 =16.8 Total = 18.8 amu

15. Brown Kidney Mac Total

16. Atomic 
Structure 
Jeopardy Hangman http://www.quia.com/hm/110454.html http://www.quia.com/cb/147081.html • http://www.quia.com/rr/70834.html