1. The Development of Atomic Theory
Chapter 3 Atomic Structure & the Periodic Table
The Development of Atomic Theory
In 1803 John Dalton proposed the “Atomic Theory” 1. All matter is made up of atoms. 2. Atoms of a particular element are similar to one another. Atoms of different elements have different properties. 3. Atoms combine in simple whole-number ratios to form compounds. 4. Chemical change involves joining, separating, or rearranging atoms. Atoms are never created or destroyed in a chemical reaction.

2. Atoms are the building blocks of all matter
Atoms are the building blocks of all matter. But, in the late 1800s, it became known that atoms were made up of subatomic particles.
particle mass (g) mass (a.m.u.) charge
proton
neutron
electron

3. Atoms have 2 regions: Nucleus -the core of the atom Electron Cloud
-contains all protons & neutrons
-all the + charge & (almost) all
the mass
Electron Cloud
-electrons (-)
-space

4. “Plum Pudding” model J.J. Thompson (1897)
cathode rays = negative particles “electrons”
“Plum Pudding” model

5. Ernst Rutherford(1911) “nuclear model”

6. Atomic Number = the number of protons in an atom

7. Mass Number = the number of protons & neutrons in an atom

8. shows the symbol, Mass Number & Atomic Number
Isotopic Notation –
shows the symbol, Mass Number & Atomic Number
of a particular Isotope of an Element
Isotopes = Atoms of the same element that have different numbers
of neutrons and therefore, different Mass Numbers

9. Isotopic Notation
Isotope Atomic Mass p no e Isotopic Number Number Notation
Magnesium-24
Magnesium-25
Magnesium-26

10. Isotopic Notation
Isotope Atomic Mass p no e Isotopic Number Number Notation
Xenon-131
Strontium-88
Potassium-39

11. Atomic Mass = weighted average of masses of all naturally-occuring isotopes of an element
Isotope Atomic Mass mass of
Number Number isotope abundance
Magnesium amu 78.70%
Magnesium amu 10.13%
Magnesium amu 11.17%

12. So, we now have 3 numbers related to the mass of an atom:
Mass Number a counted number (p + n)
Isotopic Mass a precise measure of the mass of an isotope
Atomic Mass the weighted average of the masses of all
naturally-occuring isotopes of an element
Example: There are 2 naturally-occuring isotopes of copper.
Calculate the Atomic Mass of copper, given the following:
isotope abundance mass
Cu % amu
Cu % amu

13. The Periodic Law and the Periodic Table
Periodic Law: when elements are arranged in order of increasing atomic number, elements with similar chemical properties occur at periodic intervals.

14. Figure 3.3 The periodic table of the elements is a graphical way to show relationships among the elements. Elements with similar chemical properties fall in the same vertical column.
Figure 3-3 p62

15. Characteristics of:
Metal Metalloid Nonmetal
Silver (Ag) Antimony (Sb) Sulfur (S)

16. Light & Atomic Structure
When an element is heated or exposed to a high voltage, it will give off visible light.

17. Emission Spectra
“The energy of the electron is quantized”
Neils Bohr

18. Electron Arrangement in Atoms
-electrons occupy energy levels
-only certain energy levels are allowed
-emission spectra occurs when electrons move from one energy level to another
-the region of space about the nucleus that contains electrons of approximately the same energy is called the electron shell
n = 1 lowest energy close to nucleus
n = 7 highest energy far from nucleus

19. Electron Sublevels & Orbitals
-each electron shell has one or more sublevels (subshells) s, p, d, f
-electrons in each sublevel occupy a 3-dimensional space called an Orbital
-Orbitals have unique 3-dimensional shapes
-each orbital can hold 2 electrons

21. Each subshell contains orbitals of a particular shape.
Orbitals of higher energy levels are larger and contain electrons with higher energy.
Orbital shape represents a probability density for the location of electrons
p orbital
d orbital

22. With so many shells, subshells & orbitals available, how does an electron know where to go?

23. Orbital Diagram
-fill each available orbital from the bottom to the top.
-2 electrons can fit in each orbital
-the 2 electrons have opposite “spin”
-all the orbitals of a subshell are filled singly before any orbital gets a 2nd electron

24. Electron configurationLi 3 B 5

26. The electron configuration:
- corresponds to the position of an element in the periodic table
- is responsible for the chemical behavior of an element
Distinguishing electron = the last electron added to the electron configuration

27. Element e- configuration Abbreviated Orbital DiagramMg
1s22s22p63s2
[Ne]3s2
[Ne] 12

28. Sc Element e- configuration Abbreviated configuration 21
Elements with d electrons
Element e- configuration Abbreviated
configuration Sc 21

29. Exceptions to the order of filling:
Energy levels get closer together at higher levels
Sometimes a more stable energy is attained with a single electron in the highest s subshell

30. In the 3rd period & has 2 electrons in the p subshell
Write the symbol
for the following
elements:
1s22s22p63s23p5
[Ar]4s23d8
In the 3rd period & has 2 electrons in the p subshell
Whose distinguishing electron is 3d4
In Group IIA & having 2 electons in the 7s subshell
A Noble Gas in period 5
Has 80 total electrons

31. Classification of the Elements
Based on physical properties: Metals, Nonmetals, Metalloids
Based on electron configuration: