CHM110H5- Midterm Exam Guide - Comprehensive Notes for the exam ( 13 pages long!)

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5 Oct 2017
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CHM110H5
MIDTERM EXAM
STUDY GUIDE
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ATOMIC STRUCTURE
CHAPTER 3.1!
Early History of Atomic Theories
Read chapter 3.1 from your textbook and answer the questions on the worksheet
individually.
After completing it return the textbooks If you have any questions please ask.
! !
HISTORY OF ATOM
The word “Atom” means !
“indivisible”. !
Although Greeks proposed the concept of atom in 300 B.C., it was reintroduced
by John Dalton in 1805. !
! !
HISTORY OF ATOM
JOHN DALTON’s THEORY (1805)
Also called as Billiard ball model
!
Matter is composed of indestructible, indivisible atoms, which are identical for one
element, but different from other elements.
His theory was successful at that time since it explained the laws of definite and
multiple proportions; and also the law of conservation of mass.
• •
! !
REJECTION OF DALTON’s THEORY/MODEL OF ATOM
Discovery of subatomic particles – electrons (Thompson & Milliken), protons
(Rutherford), and neutrons (Chadwick) proved that atom is further broken down into
smaller particles.
! !
THOMPSON’s MODEL OF ATOM (1897)
Also called as the “raisin bun” model or the “plum pudding” model !
Matter is composed of atoms that contain electrons (-ve) embedded in a
positive material. !
The kind of element is determined by the number of electrons in the atom. !
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! !
ERNEST RUTHERFORD’s GOLD FOIL EXPERIMENT
! !
ERNEST RUTHERFORD’s EXPERIMENT
Predicted based on Thompson’s model that alpha particles (2He4) should be deflected
at various angles.
Observed that alpha particles were deflected at large angles and even backwards from
the foil.
! !
RUTHERFORD’s Ideas!!
All of the positive charge in the atom had to be in a very small volume
compared to the size of the atom. !
There is an attractive nuclear force to keep the positive charge inside nucleus. !
The nuclear force of attraction must be stronger than the electrostatic force of
repulsion between the +ve particles. !
! !
RUTHERFORD’s MODEL (1911)
An atom is electrically NEUTRAL - made up of an equal number of –vely charged
electrons and +vely charged protons. !
Most of the mass of the atom and all of its +ve charge is contained in a tiny core
called the nucleus. !
Nucleus contains protons and neutrons that have approximately the same mass. !
! !
Question Time
Rutherford's gold foil experiment showed that the atom is mostly empty space
because:
A. some of the alpha particles were reflected right back!
B. some of the alpha particles were deflected!
C. most of the alpha particles went straight through the foil D. all of the alpha particles
went straight through the foil
ANS: C
! !
QUESTION TIME
What led Rutherford to believe that atoms contain a positive nucleus?
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Document Summary

Read chapter 3. 1 from your textbook and answer the questions on the worksheet individually. After completing it return the textbooks if you have any questions please ask. Indivisible : although greeks proposed the concept of atom in 300 b. c. , it was reintroduced by john dalton in 1805. Matter is composed of indestructible, indivisible atoms, which are identical for one element, but different from other elements. His theory was successful at that time since it explained the laws of definite and multiple proportions; and also the law of conservation of mass. Discovery of subatomic particles electrons (thompson & milliken), protons (rutherford), and neutrons (chadwick) proved that atom is further broken down into smaller particles. Thompson"s model of atom (1897: also called as the raisin bun model or the plum pudding model, matter is composed of atoms that contain electrons (-ve) embedded in a positive material. The kind of element is determined by the number of electrons in the atom.

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