The Atom Philosophy to Scientific Theory I. The Atom: Philosophy to Scientific Theory Ancient Greek...

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)


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.



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

+-

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.


Voltage source

+-

Voltage source


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

-

+


X-rays

X-rays give some droplets a charge.


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.

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