Transcript 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.
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
proton
neutron
electron
mass (g)
relative mass
charge
Atoms have 2 regions:
• Nucleus
-the core of the atom
• Electron Cloud
-electrons (-)
-contains all protons & neutrons
-space
-all the + charge & (almost) all
the mass
J.J. Thompson (1897)
cathode rays = negative particles “electrons”
“Plum Pudding” model
Ernst Rutherford(1911)
“nuclear model”
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flas
h/ruther14.swf
Atomic Number = the number of protons in an atom
Mass Number = the number of protons & neutrons in an atom
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
Isotopic Notation
Isotope
Atomic
Number
Magnesium-24
Magnesium-25
Magnesium-26
Mass
Number
p+
no
e-
Isotopic
Notation
Isotopic Notation
Isotope
Xenon-131
Strontium-88
Potassium-39
Atomic
Number
Mass
Number
p+
no
e-
Isotopic
Notation
Atomic Mass = weighted average of masses of all naturallyoccuring isotopes of an element
Isotope
Atomic
Number
Mass
Number
mass of
isotope
abundance
Magnesium-24 12
24
23.99amu
78.70%
Magnesium-25 12
25
24.99amu
10.13%
Magnesium-26 12
26
25.98amu
11.17%
Periodic Table Mass for Mg: 24.31 amu
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-occurring isotopes of an element
Example: There are 2 naturally-occurring isotopes of copper.
Calculate the Atomic Mass of copper, given the following:
isotope abundance
Cu-63
69.09%
Cu-65
30.91%
mass
62.928 amu
64.9278 amu
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.
Figure 3-3 p62
Characteristics of:
Metal
Silver (Ag)
Metalloid
Antimony (Sb)
Nonmetal
Sulfur (S)
Light & Atomic Structure
When an element is heated or exposed to a
high voltage, it will give off visible light.
Emission Spectra
“The energy of the electron is quantized”
Neils Bohr
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
n=7
lowest energy
highest energy
close to nucleus
far from nucleus
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
http://dwb4.unl.edu/chemAnime/BOHRQD/BOHRQD.html
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
With so many shells,
subshells & orbitals
available, how does
an electron know
where to go?
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
Electron configuration
3Li
5B
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
Element
12Mg
e- configuration
1s22s22p63s2
Abbreviated
configuration
[Ne]3s2
Orbital Diagram
[Ne]
Elements with d electrons
Element
21Sc
e- configuration
Abbreviated
configuration
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
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
Classification of the Elements
1.
2.
Based on physical properties: Metals, Nonmetals, Metalloids
Based on electron configuration: