Topic 1 - Matter and Energy - Revsworld

Topic 3 – The Atomic .
structure
Topic outline
In this topic, you will learn about:
.The historical development of the modern atom
. Electrons shells and electron arrangement
. The subatomic particles; protons, electrons, neutrons . Ground and excited state of atom
. Atomic number, mass number and atomic mass . Bright-line spectra
. Isotopes and isotopes symbols . Valance electrons, neutral atoms and ions
Introduction:
Lesson 1 - The historical development of the modern atom
The atom is the most basic unit of matter. Since atoms are very small and cannot be seen with the most
sophisticated equipment, several scientists, for thousands of years have proposed different models of
atoms to help explain the nature and behavior of matter.
In this lesson, you will learn about these historical scientists, their experiments and their proposed
models of atom.
1. Historical development of atom: Definitions and facts
Concept Facts: Study to remember the following about the development of the modern atom.
. Many scientists over many years have contributed to the development of the modern atomic model.
. The wave mechanical-model is the current and the most widely accepted model of the atom.
The wave-mechanical model of an atom is summarized below.
. Each atom has small dense positive nucleus
. Electrons are found outside the nucleus in a region called an orbital.
. An Orbital is the most probable location of finding an electron with certain energy in an atom.
Below are the historical scientists and their proposed models of the atom starting with the
earliest. Description of model and key feature for each model are given below the atom.
Concept Facts: Study to remember the order of atomic model starting with the earliest model.
John Dalton J.J. Thompson Earnest Rutherford Neil Bohr Current model
(Earliest model)
- + - + -
+- + - +
-+ - + - + -
+ -+ - + - +
+ - + - + -+
+ +
orbital
Hard-sphere model
(cannonball)
.No internal structure
Plum-pudding model
.Electrons and positive
charges disperse
throughout the atom.
Empty-space model
(Nuclear model)
.Small dense positive
nucleus
. Electrons revolve
around the nucleus
Bohr’s model
(Planetary)
. Electrons in specific orbit
. Orbits have fixed energy
.Orbits create electron shells
Wave-mechanical
(electron cloud)
.Electrons in orbital
. Orbital is area
electron is likely
to be found
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