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Chapter 2

CHEM 1010U Chapter Notes - Chapter 2: Chemical Substance, Chemical Formula, Weighted Arithmetic Mean


School
UOIT
Department
Chemistry
Course Code
CHEM 1010U
Professor
ifa
Chapter
2

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Chemistry 1010 Chapter 2: Atoms, Molecules and Ions Thursday Sept 8th, 2014
Understanding Matter:
Element: a basic substance that can’t be simplified
Can’t be chemically changed or broken down into something simpler
Hydrogen, oxygen, etc. (found on periodic table)
Atom : the smallest amount of an element
The basic building blocks of ordinary matter
Can join together to form molecules which form most of the objects around you
Is made up of electrons, protons, and neutrons
The 3 Laws:
1. Law of Mass Conservation
When combustion is carried out in a closed container, the mass of the starting reactants
equals that of the products
Hg(NO3)2 + 2KI  HgI2 + 2KNO3
Mercury Nitrate Potassium Iodide Mercury iodide Potassium nitrate
3.32g 3.25g 4.55g 2.02g
6.57 g 6.57g
Mass is neither created nor destroyed in chemical reactions
2. Law of Definite Proportions
Different samples of a pure chemical substance always contain the same proportions of
elements by mass
H2O
H (1.0 x2) =2.02

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Chemistry 1010 Chapter 2: Atoms, Molecules and Ions Thursday Sept 8th, 2014
+O (16x1) =16.0
= 18.02
2.02/18.02 x 100 = 11%
16/18.02 x 100 = 88.8%
CO2
C (12.01) =12.01
O (16.00 x2) =32.00
32.00+12.01=44.01
12.01/44.01 x100= 27%
32/44.01 x 100= 72.7%
3. Law of Multiple Proportions
Elements can combine in different ways to form different substances, whose mass
ratios are small whole number multiples of each other
There were discreet units on atoms that could combine in different ways
7 grams of N per 8 grams of O
7 grams of N per 16 grams of O
Multiple of 1 multiple of 2
Don’t get bogged down on this
Led to DA theory
Dalton’s Atomic Theory
John Dalton (1766 – 1844)
1. Elements are made up of tiny particles called atoms

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Chemistry 1010 Chapter 2: Atoms, Molecules and Ions Thursday Sept 8th, 2014
2. Each element is characterized by the mass of its atoms
Atoms of the same element have the same mass but atoms of different elements
have a different mass
3. Chemical combination of elements to make different substances occurs when atoms join
together in small whole number ratios
Only whole numbers of atoms combine – fractional parts of atoms are never
involved
4. Chemical reactions only rearrange the way that atoms are combined; the atoms
themselves don’t change
The structure of an Atom: Discovery of the Electron
Dalton’s atomic theory said nothing about the components of the atom (electron, neutron,
and proton)
J.J. Thompson (1856 – 1940)
Cathode-ray tube
There are 3 factors that affect how the beam deflexed
1. Strength of the deflecting magnetic or electric field
2. Size of the negative charge in the electron (negative magnet will repel the negative side
of the pole way more because of its size (strength)
3. Mass of the electron
Defined the charge (e) to mass (m) ratio of the electron = e/m= 1.758820 X 108 C/g
-e =1.602176*10^19 C
-mass of an electron is =9.1093382 X 10-38 grams
The structure of an Atom: Protons and Neutrons
Atomic Nucleus: Ernest Rutherford (1871-1937) bombarded gold foil with alpha
particles
Although most of the alpha
particles passed through the
foil undeflected,
approximately 1 in every
20,000 particles were
deflected
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