The AtomThe Atom
Philosophy to Scientific Theory
Philosophy to Scientific Theory
I. The Atom: Philosophy to
Scientific Theory
I. The Atom: Philosophy to
Scientific Theory Ancient Greek
Philosophers theorized on what the universe was made of
Democritus (450-370 BC) Sand can be broken
down into tiny indivisible components -- “atomos”
Ancient Greek Philosophers theorized on what the universe was made of
Democritus (450-370 BC) Sand can be broken
down into tiny indivisible components -- “atomos”
Aristotle (384-322 BC)
Did not believe in the atomos theory
Believed all matter was continuous No void exists 5 elements Aristotle’s views
influenced Western thought for 2000 yrs.
Aristotle (384-322 BC)
Did not believe in the atomos theory
Believed all matter was continuous No void exists 5 elements Aristotle’s views
influenced Western thought for 2000 yrs.
Early Modern Times/Enlightenment
Early Modern Times/Enlightenment
Aristotle’s ideas questioned Sir Francis Bacon (1561-1626)
developed the Scientific Method Early alchemist
Works of Robert Boyle (1627-1691) led to the belief of more than four elements existing
Aristotle’s ideas questioned Sir Francis Bacon (1561-1626)
developed the Scientific Method Early alchemist
Works of Robert Boyle (1627-1691) led to the belief of more than four elements existing
Late 1700’sLate 1700’s All chemists accepted
the modern definition of an element
1790’s -Antoine Lavoisier-father of Modern Chemistry Stated the law of
conservation of mass
Recognized and named oxygen and hydrogen
All chemists accepted the modern definition of an element
1790’s -Antoine Lavoisier-father of Modern Chemistry Stated the law of
conservation of mass
Recognized and named oxygen and hydrogen
Late 1700’sLate 1700’s
Emphasis placed on quantitative analysis
Led to discovery of the conservation of mass
Law of multiple proportions Law of definite proportions
Emphasis placed on quantitative analysis
Led to discovery of the conservation of mass
Law of multiple proportions Law of definite proportions
Dalton’s atomic theoryDalton’s atomic theory
1808 English schoolteacher
Applied the law of conservation of mass, the law of multiple and definite proportions
1808 English schoolteacher
Applied the law of conservation of mass, the law of multiple and definite proportions
Dalton’s atomic theoryDalton’s atomic theory
1. All matter is composed of extremely small particles called atoms.
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
1. All matter is composed of extremely small particles called atoms.
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)
Dalton’s atomic theory (cont’d)
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple whole number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged.
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple whole number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged.
Dalton’s atomic theory (cont’d)
Dalton’s atomic theory (cont’d)
Some of Dalton’s theories were disproved.
Which ones? How did Dalton “visualize” the
atom at this time? The atom is impossible to see-
instruments must be used to indirectly see.
Some of Dalton’s theories were disproved.
Which ones? How did Dalton “visualize” the
atom at this time? The atom is impossible to see-
instruments must be used to indirectly see.
Experiments to determine what an atom was
Experiments to determine what an atom was
J. J. Thomson- used Cathode ray tubes
J. J. Thomson- used Cathode ray tubes
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive end.positive end.
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field, he found that By adding an electric field, he found that the moving pieces were negative the moving pieces were negative
+
-
Thomson’s ModelThomson’s Model
Found the electron. Couldn’t find
positive (for a while).
Said the atom was like plum pudding.
A bunch of positive stuff, with the electrons able to be removed.
Found the electron. Couldn’t find
positive (for a while).
Said the atom was like plum pudding.
A bunch of positive stuff, with the electrons able to be removed.
Millikan’s ExperimentMillikan’s Experiment
Oil
Atomizer
Oil droplets
Telescope
-
+
Millikan’s ExperimentMillikan’s Experiment
X-rays
X-rays give some droplets a charge.
Millikan’s ExperimentMillikan’s Experiment
Some drops would hoverFrom the mass of the drop and the charge on the plates, he calculated the mass of an electron
RadioactivityRadioactivity
Discovered by accident Bequerel Three types
alpha- helium nucleus (+2 charge, large mass)
beta- high speed electron gamma- high energy light
Discovered by accident Bequerel Three types
alpha- helium nucleus (+2 charge, large mass)
beta- high speed electron gamma- high energy light
Rutherford’s ExperimentRutherford’s Experiment
Used uranium to produce alpha particles.
Aimed alpha particles at gold foil by drilling hole in lead block.
Since the mass is evenly distributed in gold atoms alpha particles should go straight through.
Used gold foil because it could be made atoms thin.
Used uranium to produce alpha particles.
Aimed alpha particles at gold foil by drilling hole in lead block.
Since the mass is evenly distributed in gold atoms alpha particles should go straight through.
Used gold foil because it could be made atoms thin.
Lead block
Uranium
Gold Foil
Florescent Screen
What he expected
Because
Because, he thought the mass was evenly distributed in the atom.
What he got
How he explained it
+
Atom is mostly empty Small dense,
positive pieceat center.
Alpha particlesare deflected by
it if they get close enough.
Atom is mostly empty Small dense,
positive pieceat center.
Alpha particlesare deflected by
it if they get close enough.
+
Modern View of the AtomModern View of the Atom
The atom is mostly empty space.
Two regions Nucleus- protons
and neutrons. Electron cloud-
region where you might find an electron.
The atom is mostly empty space.
Two regions Nucleus- protons
and neutrons. Electron cloud-
region where you might find an electron.
Sub-atomic ParticlesSub-atomic Particles
Z - atomic number = number of protons determines type of atom.
A - mass number = number of protons + neutrons.
Number of protons = number of electrons if neutral.
Z - atomic number = number of protons determines type of atom.
A - mass number = number of protons + neutrons.
Number of protons = number of electrons if neutral.
SymbolsSymbols
XA
Z
Na23
11
IsotopesIsotopes
Atoms of the same element that have different masses because of different number of neutrons. Ex/Hydrogen
Nuclide- a general term for a specific isotope of an element.
Atoms of the same element that have different masses because of different number of neutrons. Ex/Hydrogen
Nuclide- a general term for a specific isotope of an element.
IsotopeIsotope
Compounds are made of two or more atoms or ions chemically combined.
Can a compound be made of different isotopes?
Compounds are made of two or more atoms or ions chemically combined.
Can a compound be made of different isotopes?
Relative Atomic MassesRelative Atomic Masses
Masses of atoms in grams are very small.
Chemists use a more convenient unit The atomic mass unit or amu
One amu is equal to exactly one twelfth the mass of a carbon-12 atom Hydrogen-1 is about 1/12 th e mass of
carbon-12 1.007825 amu
Masses of atoms in grams are very small.
Chemists use a more convenient unit The atomic mass unit or amu
One amu is equal to exactly one twelfth the mass of a carbon-12 atom Hydrogen-1 is about 1/12 th e mass of
carbon-12 1.007825 amu
Average Atomic MassAverage Atomic Mass
Most elements occur naturally as mixtures of isotopes.
Isotopes occur in different percentages.
Average atomic mass is the weighted average of the naturally occurring isotopes of an element.
Most elements occur naturally as mixtures of isotopes.
Isotopes occur in different percentages.
Average atomic mass is the weighted average of the naturally occurring isotopes of an element.
Relating Mass to Numbers of Atoms
Relating Mass to Numbers of Atoms
The Mole Avogadro’s number Molar Mass Mass to Mole conversions Mole to number of particle
conversions
The Mole Avogadro’s number Molar Mass Mass to Mole conversions Mole to number of particle
conversions
The Mole The Mole
Abbreviation for molecule 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.
Counting unit-similar to a dozen A mole contains 6.022 X 1023
particles
Abbreviation for molecule 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.
Counting unit-similar to a dozen A mole contains 6.022 X 1023
particles
Avogadro’s numberAvogadro’s number
Avogadro’s number is the number of particles in exactly one mole of a pure substance.
6.022 X 1023
Named after Italian scientist Amedeo Avogadro
Avogadro’s number is the number of particles in exactly one mole of a pure substance.
6.022 X 1023
Named after Italian scientist Amedeo Avogadro
Relevance of Avog. number
Relevance of Avog. number
Related the microscopic to the macroscopic
Brought the amu (1/12 mass of Carbon-12) definition together with the gram
How many particles do you need to equal 12 grams of Carbon-12?
1 gram = 1 atomic mass unit
Related the microscopic to the macroscopic
Brought the amu (1/12 mass of Carbon-12) definition together with the gram
How many particles do you need to equal 12 grams of Carbon-12?
1 gram = 1 atomic mass unit
Relevance of Avagadro’s #
Relevance of Avagadro’s #
1 amu is equal to exactly one twelth the mass of a carbon-12 atom
One mole is the amount of a substance that contains as many particles as there are atoms in exactly 12 grams of carbon-12
So. . .
1 amu is equal to exactly one twelth the mass of a carbon-12 atom
One mole is the amount of a substance that contains as many particles as there are atoms in exactly 12 grams of carbon-12
So. . .
1 amu = 1/12 mass of Carbon-121 mole = # in 12 grams of Carbon-
12How much does 1/12 of a mole of
Carbon-12 weigh?1 gramIf we are talking on the atomic level,
we use amuIf we are in the lab, we use grams
and moles
1 amu = 1/12 mass of Carbon-121 mole = # in 12 grams of Carbon-
12How much does 1/12 of a mole of
Carbon-12 weigh?1 gramIf we are talking on the atomic level,
we use amuIf we are in the lab, we use grams
and moles
Molar MassMolar Mass
The mass of one mole of a pure substance.
Do not confuse with atomic mass Same number but . . . Atomic mass is measured in amu Molar mass is in grams
The mass of one mole of a pure substance.
Do not confuse with atomic mass Same number but . . . Atomic mass is measured in amu Molar mass is in grams
Conversion factors from these definitions
Conversion factors from these definitions
1 mole = 6.022 X 1023
1 mole = molar mass of the elementMolar mass number is equal to the average atomic mass but in grams instead of amu
Average atomic was calculated from isotopes and percent abundances
1 mole = 6.022 X 1023
1 mole = molar mass of the elementMolar 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 conversionsGram to mole conversions
How many moles of calcium are in 5.00 g of Calcium?
How many moles of gold are in 3.6 mg of gold?
How many moles of zinc are in .535 g of zinc?
How many moles of calcium are in 5.00 g of Calcium?
How many moles of gold are in 3.6 mg of gold?
How many moles of zinc are in .535 g of zinc?
Mole to mass conversionsMole to mass conversions
What is the mass in grams of 2.25 mol of the element Fe.
What is the mass in grams of .375 mol of the element K?
What is the mass in gram of 0.0135 mol of the element Na?
What is the mass in grams of 2.25 mol of the element Fe.
What is the mass in grams of .375 mol of the element K?
What is the mass in gram of 0.0135 mol of the element Na?
Mole to particle conversions
Mole to particle conversions
Particles can be molecules, atoms, or formula units.
How many atoms of Al are in 2.75 mol of aluminum?
How many atoms of S are in 3.00 mol of Sulfur?
Particles can be molecules, atoms, or formula units.
How many atoms of Al are in 2.75 mol of aluminum?
How many atoms of S are in 3.00 mol of Sulfur?
Particles to Mole conversions
Particles to Mole conversions
How many moles of Pb are in 1.50 X 1012 atoms?
How many moles of Sn are in 2500 atoms of tin?
How many moles of Pb are in 1.50 X 1012 atoms?
How many moles of Sn are in 2500 atoms of tin?
Mass to particle conversions
Mass to particle conversions
Helps us count by weight Different Molar masses because elements
weigh differently (# protons and # neutrons)
How many atoms are in 3.2 grams of He? How many molecules are in 16.0 grams of
Oxygen? How many atoms are in 16.0 grams of
Oxygen (diatomic)?
Helps us count by weight Different Molar masses because elements
weigh differently (# protons and # neutrons)
How many atoms are in 3.2 grams of He? How many molecules are in 16.0 grams of
Oxygen? How many atoms are in 16.0 grams of
Oxygen (diatomic)?
Chemical BondsChemical Bonds
The forces that hold atoms together. Covalent bonding - sharing electrons. Makes molecules. Chemical formula- the number and type
of atoms in a molecule. C2H6 - 2 carbon atoms, 6 hydrogen atoms,
Structural formula shows the connections, but not necessarily the shape.
The forces that hold atoms together. Covalent bonding - sharing electrons. Makes molecules. Chemical formula- the number and type
of atoms in a molecule. C2H6 - 2 carbon atoms, 6 hydrogen atoms,
Structural formula shows the connections, but not necessarily the shape.
H
H
H H
H
HC C
There are also other model that attempt to show three dimensional shape.
Ball and stick.
There are also other model that attempt to show three dimensional shape.
Ball and stick.
IonsIons
Atoms or groups of atoms with a charge.
Cations- positive ions - get by losing electrons(s).
Anions- negative ions - get by gaining electron(s).
Ionic bonding- held together by the opposite charges.
Ionic solids are called salts.
Atoms or groups of atoms with a charge.
Cations- positive ions - get by losing electrons(s).
Anions- negative ions - get by gaining electron(s).
Ionic bonding- held together by the opposite charges.
Ionic solids are called salts.