Download The Atom Philosophy to Scientific Theory

The Atom
Philosophy to
Scientific Theory
I. The Atom:
Philosophy to Scientific
Theory
s Ancient Greek
Philosophers
theorized on what the
universe was made of
s Democritus (450-370
BC)
s Sand can be broken
down into tiny
indivisible
components -“atomos”
s Aristotle (384-322
BC)
s Did not believe in
the atomos theory
s Believed all matter
was continuous
s No void exists
s 5 elements
s Aristotle’s views
influenced
Western thought
for 2000 yrs.
Early Modern Times/
Enlightenment
s Aristotle’s ideas questioned
s Sir Francis Bacon (1561-1626) developed the
Scientific Method
s Early alchemist
s Works of Robert Boyle (1627-1691) led to the
belief of more than four elements existing
Late 1700’s
s All chemists
accepted the
modern definition
of an element
s 1790’s -Antoine
Lavoisier-father
of Modern
Chemistry
s Stated the law
Late 1700’s
s Emphasis placed on quantitative
analysis
s Led to discovery of the conservation of
mass
s Law of multiple proportions
s Law of definite proportions
Dalton’s atomic theory
s 1808 English
schoolteacher
s Applied the law
of conservation
of mass, the law
of multiple and
definite
proportions
Dalton’s atomic theory
s 1. All matter is composed of extremely
small particles called atoms.
s 2. Atoms of a given element are
identical in size, mass, and other
properties; atoms of different
elements differ in size, mass, and
other properties
Dalton’s atomic theory
(cont’d)
s 3. Atoms cannot be subdivided,
created, or destroyed.
s 4. Atoms of different elements
combine in simple whole number ratios
to form chemical compounds.
s 5. In chemical reactions, atoms are
combined, separated, or rearranged.
Dalton’s atomic theory
(cont’d)
s Some of Dalton’s theories were
disproved.
s Which ones?
s How did Dalton “visualize” the atom at
this time?
s The atom is impossible to seeinstruments must be used to indirectly
see.
Experiments to determine
what an atom was
s J. J. Thomson- used Cathode ray tubes
Thomson’s Experiment
-
Voltage source
+
Thomson’s Experiment
-
Voltage source
+
Thomson’s Experiment

Voltage source
+
Passing an electric current makes a beam
appear to move from the negative to the
positive end.
Thomson’s Experiment
Voltage source
+
 By adding an electric field, he found that
the moving pieces were negative
Thomson’s Model
s Found the electron.
s Couldn’t find positive
(for a while).
s Said the atom was like
plum pudding.
s A bunch of positive
stuff, with the
electrons able to be
removed.
Millikan’s Experiment
Atomizer
Oil droplets
+
Oil
Telescope
Millikan’s Experiment
X-rays
X-rays give some droplets a charge.
Millikan’s Experiment
From
thedrops
masswould
of the hover
drop and the charge on
Some
the plates, he calculated the mass of an electron
Radioactivity
s Discovered by accident
s Bequerel
s Three types
s alpha- helium nucleus (+2 charge, large
mass)
s beta- high speed electron
s gamma- high energy light
Rutherford’s Experiment
s Used uranium to produce alpha particles.
s Aimed alpha particles at gold foil by drilling
hole in lead block.
s Since the mass is evenly distributed in gold
atoms alpha particles should go straight
through.
s Used gold foil because it could be made
atoms thin.
Lead
block
Uranium
Florescent
Screen
Gold Foil
What he expected
Because
Because, he thought the mass was
evenly distributed in the atom. (Plum
Pudding model)
What he observed
What he concluded:
s Atom is mostly empty
s Small dense,
positive piece
at center.
s named it the nucleus
+
+
Modern View of the Atom
s The atom is mostly
empty space.
s Two regions
s Nucleus- protons
and neutrons.
s Electron cloudregion where you
might find an
electron.
Sub-atomic Particles
s Z - atomic number = number of protons
determines type of atom.
s A - mass number = number of protons +
neutrons.
s Number of protons = number of
electrons if neutral.
Symbols
A
X
Na
11
Z
23
Isotopes
s Atoms of the same element that have
different masses because of different
number of neutrons. Ex/Hydrogen
s Nuclide- a general term for a specific
isotope of an element.
Isotope
s Compounds are made of two or more
atoms or ions chemically combined.
s Can a compound be made of different
isotopes?
Made of deuterium oxide
Heavy Ice Sinks
Relative Atomic Masses
s Masses of atoms in grams are very small.
s Chemists use a more convenient unit
s The atomic mass unit or amu
s One amu is equal to exactly one twelfth the
mass of a carbon-12 atom
s Hydrogen-1 is about 1/12 th
carbon-12
s 1.007825 amu
e mass of
Average Atomic Mass
s Most elements occur naturally as
mixtures of isotopes.
s Isotopes occur in different
percentages.
s Average atomic mass is the weighted
average of the naturally occurring
isotopes of an element.
Relating Mass to Numbers of
Atoms
s
s
s
s
s
The Mole
Avogadro’s number
Molar Mass
Mass to Mole conversions
Mole to number of particle conversions
The Mole
s Abbreviation for molecule
s A mole (mol) is the amount of a
substance that contains as many
particles as there are atoms in exactly
12 grams of carbon-12.
s Counting unit-similar to a dozen
s A mole contains 6.022 X 1023 particles
Avogadro’s number
s Avogadro’s number is the number of
particles in exactly one mole of a pure
substance.
s 6.022 X 1023
s Named after Italian scientist Amedeo
Avogadro
Relevance of Avog. number
s Related the microscopic to the
macroscopic
s Brought the amu (1/12 mass of
Carbon-12) definition together with the
gram
s How many particles do you need to
equal 12 grams of Carbon-12?
s 1 gram = 1 atomic mass unit
Needs more clarification
Relevance of Avagadro’s #
s 1 amu is equal to exactly one twelth
the mass of a carbon-12 atom
s One mole is the amount of a substance
that contains as many particles as
there are atoms in exactly 12 grams of
carbon-12
s So. . .
1 amu = 1/12 mass of Carbon-12
1 mole = # in 12 grams of Carbon-12
How much does 1/12 of a mole of
Carbon-12 weigh?
1 gram
If we are talking on the atomic level, we
use amu
If we are in the lab, we use grams and
moles
Molar Mass
s The mass of one mole of a pure
substance.
s Do not confuse with atomic mass
s Same number but . . .
s Atomic mass is measured in amu
s Molar mass is in grams
Conversion factors from these
definitions
s 1 mole = 6.022 X 1023
s 1 mole = molar mass of the element
Molar mass number is equal to the
average atomic mass but in grams
instead of amu
Average atomic was calculated from
isotopes and percent abundances
Gram to mole conversions
s How many moles of calcium are in 5.00
g of Calcium?
s How many moles of gold are in 3.6 mg
of gold?
s How many moles of zinc are in .535 g
of zinc?
Mole to mass conversions
s What is the mass in grams of 2.25 mol
of the element Fe.
s What is the mass in grams of .375 mol
of the element K?
s What is the mass in gram of 0.0135 mol
of the element Na?
Mole to particle conversions
s Particles can be molecules, atoms, or
formula units.
s How many atoms of Al are in 2.75 mol
of aluminum?
s How many atoms of S are in 3.00 mol
of Sulfur?
Particles to Mole conversions
s How many moles of Pb are in 1.50 X
1012 atoms?
s How many moles of Sn are in 2500
atoms of tin?
Mass to particle conversions
s Helps us count by weight
s Different Molar masses because elements
weigh differently (# protons and # neutrons)
s How many atoms are in 3.2 grams of He?
s How many molecules are in 16.0 grams of
Oxygen?
s How many atoms are in 16.0 grams of
Oxygen (diatomic)?
Chemical Bonds
s
s
s
s
The forces that hold atoms together.
Covalent bonding - sharing electrons.
Makes molecules.
Chemical formula- the number and type of
atoms in a molecule.
s C2H6 - 2 carbon atoms, 6 hydrogen atoms,
s Structural formula shows the connections,
but not necessarily the shape.
H
H C
H
H
C H
H
s There are also other model that
attempt to show three dimensional
shape.
s Ball and stick.
Ions
s Atoms or groups of atoms with a charge.
s Cations- positive ions - get by losing
electrons(s).
s Anions- negative ions - get by gaining
electron(s).
s Ionic bonding- held together by the opposite
charges.
s Ionic solids are called salts.