Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Lecture Notes on Dalton's Atomic Theory | CHM 121, Study notes of Chemistry

Notes6 Material Type: Notes; Professor: Kidwell; Class: GENERAL CHEMISTRY I; Subject: Chemistry; University: Harper College; Term: Spring 2015;

Typology: Study notes

2014/2015

Uploaded on 02/02/2015

dantherussky97
dantherussky97 🇺🇸

6 documents

1 / 6

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Dalton’s Atomic Theory
In 1808, Dalton presented his theory of atoms:
Paraphrasing:
1) Each element is made up of tiny particles called atoms
2) The atoms of a given element are identical; the atoms of different
elements are different in some fundamental way or ways
3) Chemical compounds are formed when atoms of different elements
combine with each other. A given compound always has the same
relative numbers and types of atoms
4) Chemical reactions involve reorganization of the atoms – changes in
the way they are bound together. The atoms themselves are not
changed in a chemical reaction
Beyond this, he made an important assumption;
That nature was as simple as possible
Although this assumption was inaccurate it did lead him to some useful
results
He was able to prepare the first table of atomic masses (weights)
The large step in science was made by Joseph Gay-Lussac (1809)
He observed that at the same temperature and pressure 2 volumes of
hydrogen gas reacted with 1 volume of oxygen gas
This work was closely followed by Amadeo Avogadro (1811) who proposed
(from Lussacs’ results) that:
At the same temperature and pressure, equal volumes of different gases
contain the same number of particles (Avogadro’s Hypothesis)
Avogadro’s Hypothesis led to the following relation:
If;
2 volumes of hydrogen + 1 volume of oxygen → 2 volumes of water
pf3
pf4
pf5

Partial preview of the text

Download Lecture Notes on Dalton's Atomic Theory | CHM 121 and more Study notes Chemistry in PDF only on Docsity!

Dalton’s Atomic Theory

In 1808 , Dalton presented his theory of atoms: Paraphrasing:

  1. Each element is made up of tiny particles called atoms
  2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways
  3. Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms
  4. Chemical reactions involve reorganization of the atoms – changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction Beyond this, he made an important assumption; That nature was as simple as possible Although this assumption was inaccurate it did lead him to some useful results He was able to prepare the first table of atomic masses ( weights ) The large step in science was made by Joseph Gay-Lussac (1809) He observed that at the same temperature and pressure 2 volumes of hydrogen gas reacted with 1 volume of oxygen gas This work was closely followed by Amadeo Avogadro (1811) who proposed (from Lussacs’ results) that: At the same temperature and pressure, equal volumes of different gases

contain the same number of particles ( Avogadro’s Hypothesis )

Avogadro’s Hypothesis led to the following relation: If; 2 volumes of hydrogen + 1 volume of oxygen → 2 volumes of water

Then; 2 molecules of hydrogen + 1 molecule of oxygen → 2 molecules of water

Early Experiments to Characterize the Atom

Based on all of this work the idea of “the atom” was clearly a good one. So the next logical step should be to ask: What is an atom?

He then used this beam in an applied magnetic field to determine the charge-to-mass ratio of an electron

e/m = -1.76 x 10

8

C/g

He reasoned since all metal electrodes produced “ cathode rays ” that all elements must contain electrons Also, that there must also be positive charges present and that the electrons are randomly embedded in the “ positive cloud ” This is called the “ Plum pudding ” model of the atom The next major advancement in understanding came when Robert Millikan

(1909) performed his Oil Drop Experiment

This allowed him to determine the magnitude of the e

  • charge The e

charge combined with the charge-to-mass ratio of the electron by Thomson allowed him to calculate the mass of an electron

Mass of e

-

= 9.11 x 10

-

kg

Radioactivity

First recognized in 1896 by Henri Becquerel He followed this observation to discover three types:

  1. Alpha particles (α) – particles with a 2) – particles with a 2

charge (7300 times the e

mass) Now we know it as a He nucleus

  1. Beta particles (β) – high speed electrons) – high speed electrons
  2. Gamma rays (γ) – high energy light (electromagnetic)) – high energy light (electromagnetic)