Download Intro To Atomic Theory

Introduction to
Atomic Theory
Some old people, facial hair and some
science
Aristotle
• Various combinations of simple properties existed as
undifferentiated matter to create every substance
known
• Water, air, fire and earth
Dalton’s Atomic Theory
• Elements are all made up of small particles called
atoms
• All atoms of a particular molecule are identical
• Chemical compounds are unique and are made
up of a particular combination of specific atoms,
put together in a specific way
• Chemical reactions are reshuffling of atoms to
create new compounds. The new compounds are
made of the original atoms in the reaction
Law of Definite
Proportions
• Pure samples of a particular compound always
contain the same proportions by mass of the
elements in the compound
Law of Multiple
Proportions
• When different masses of one element combine
with a specific mass of a second element, the mass
ratios of the first element are small whole number
ratios.
Law of Conservation
• The mass of reactants and products are the same
J.J. Thomson
• Spherical ball of positive
charge with negative charges
buried inside.
• Discovered the electron
• Plum Pudding model. Also
known as the chocolate chip
cookie model.
RutherfordGeiger-Marsden
• Very important experiment in figuring out the atom
Gold Foil Experiment
• Fired alpha particles at thin sheet of gold foil
• Some of the alpha particles bounced off at strange
angles
• Showed there was a concentration of mass in the
atom: the nucleus
Atom Structure
• Atom is made up of tiny
positively charged nucleus
• Nucleus is surrounded by
negatively charged
electrons
• Almost all the mass of the
atom is in the form of
protons and neutrons
• # protons = # electrons to
give it a neutral charge
Atomic Number and
Atomic Mass
• Atomic number: The number of protons in an atom
OR charge on the nucleus
• Neutral atoms: # electrons = # protons
• Ion: If electrons are added or removed from a
neutral atom, then it is called an ion
On the Periodic Table
• Atomic Number: Always a whole number
• Atomic Symbol
• Atomic mass: Always a decimal number
o # of protons + # of neutrons
o Electrons are so light they are negligible
Isotopes
• Isotopes are different flavors of the same element
• Same # protons, different # of neutrons
• Example: Hydrogen, deuterium and tritium
Mixtures of Isotopes
• The reason we have decimal points for the masses
on the periodic table is because they are averages
of the different isotopes
• Example:
Chlorine is a mixture, which is
75.77% Cl-35
24.33% Cl-37
Calculation:
The molar mass of Cl-35 is 34.968852g and Cl-37 is
36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of
chlorine is Cl-37, what is the average molar mass of
the chlorine atom in such a mixture?
Calculation:
The molar mass of Cl-35 is 34.968852g and Cl-37 is
36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of
chlorine is Cl-37, what is the average molar mass of
the chlorine atom in such a mixture?
Take the percent average
Calculation:
The molar mass of Cl-35 is 34.968852g and Cl-37 is
36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of
chlorine is Cl-37, what is the average molar mass of
the chlorine atom in such a mixture?
Take the percent average
Mass of Cl-35= 75.77% x 34.968852 = 26.4959
Mass of Cl-37= 24.23% x 26.865803 = 8.9568
Calculation:
The molar mass of Cl-35 is 34.968852g and Cl-37 is
36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of
chlorine is Cl-37, what is the average molar mass of
the chlorine atom in such a mixture?
Take the percent average
Mass of Cl-35= 75.77% x 34.968852 = 26.4959
Mass of Cl-37= 24.23% x 36.965803 = 8.9568
Total mass of mixture = 26.4959+8.9568 = 35.453g
Two Projects
One
big, one
small
Small Project
• Using the atomic number you have drawn from the
hat, please make an 8.5x11 periodic box
• Include:
o
o
o
o
o
o
Name of Element
Atomic Symbol
Atomic Mass
Some different isotopes and their uses
A picture representing the element
Leave a third of the page open, as we will be adding onto this later down
the road
This will also be posted online on my website
Big Project!
• Research a scientist who was instrumental in figuring
out what we know now about the atom.
• Work in teams of 3 or 4
• Please sign up at the front with Mr. Lam. Know:
o
o
o
o
Your teammates
Your team name
The scientist you want to research
How you may want to present it