Leadoff QuestionLeadoff Question

How many atoms in one How many atoms in one mole of Carbon?mole of Carbon?

October 29, 2015October 29, 2015

Chapter 4: AtomsChapter 4: Atoms

99thth Grade Physical Science Grade Physical Science

Atomos: Not to Be CutAtomos: Not to Be Cut

The History of Atomic TheoryThe History of Atomic Theory

Investigating Atoms and Atomic Investigating Atoms and Atomic TheoryTheory

Atomic ModelsAtomic Models This model of the This model of the

atom may look atom may look familiar to you. This is familiar to you. This is the Bohr model. In the Bohr model. In this model, the this model, the nucleus is orbited by nucleus is orbited by electrons, which are electrons, which are in different energy in different energy levels. levels. A model uses familiar ideas to A model uses familiar ideas to

explain unfamiliar facts explain unfamiliar facts observed in nature.observed in nature.

A model can be changed as A model can be changed as new information is collected.new information is collected.

The atomic model The atomic model has changed has changed throughout the throughout the centuries, starting centuries, starting in 400 BC, when it in 400 BC, when it looked like looked like a a billiard ball billiard ball →→

Who are these men?Who are these men?

In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.

DemocritusDemocritus

This is the Greek This is the Greek philosopher Democritus philosopher Democritus who began the search for who began the search for a description of matter a description of matter more than more than 24002400 years ago. years ago. He asked: Could matter He asked: Could matter

be divided into smaller be divided into smaller and smaller pieces and smaller pieces forever, or was there a forever, or was there a limitlimit to the number of to the number of times a piece of matter times a piece of matter could be could be divideddivided? ?

400 BC

AtomosAtomos

His theory: Matter could not His theory: Matter could not be divided into smaller and be divided into smaller and smaller pieces forever, smaller pieces forever, eventually the smallest eventually the smallest possible piece would be possible piece would be obtained.obtained.

This piece would be This piece would be indivisible.indivisible.

He named the smallest He named the smallest piece of matter “atomos,” piece of matter “atomos,” meaning “not to be cut.”meaning “not to be cut.”

AtomosAtomos

To Democritus, atoms To Democritus, atoms were were smallsmall, hard , hard particles that were all particles that were all made of the same made of the same material but were material but were differentdifferent shapes and shapes and sizes.sizes.

Atoms were Atoms were infiniteinfinite in in number, always number, always moving and capable of moving and capable of joining together.joining together.

This theory was This theory was ignored and forgotten ignored and forgotten for more than for more than 2000 2000 years!years!

Why?Why?The eminent The eminent philosophers of philosophers of the time, the time, AristotleAristotle and and Plato, had a Plato, had a more more respected, respected, (and ultimately (and ultimately wrongwrong) theory.) theory. Aristotle and Plato favored the earth,

fire, air and water approach to the nature of matter. Their ideas held sway because of their eminence as philosophers. The atomos idea was buried for approximately 2000 years.

Dalton’s ModelDalton’s Model

In the early 1800s, In the early 1800s, the English the English Chemist John Chemist John Dalton Dalton performed a performed a number of number of experiments that experiments that eventually led to eventually led to the acceptance of the acceptance of the idea of atoms.the idea of atoms.

Dalton’s TheoryDalton’s Theory

He deduced that all He deduced that all elementselements are composed of are composed of atoms. Atoms are atoms. Atoms are indivisible and indivisible and indestructible particles.indestructible particles.

Atoms of the Atoms of the samesame element element are exactly alike.are exactly alike.

Atoms of Atoms of differentdifferent elements elements are are differentdifferent..

CompoundsCompounds are formed by are formed by the joining of atoms of two the joining of atoms of two or more elements.or more elements.

..

This theory This theory became one became one of the of the foundations foundations of modern of modern chemistry.chemistry.

Thomson’s Plum Pudding Thomson’s Plum Pudding ModelModel

In In 18971897, the , the English scientist English scientist J.J. Thomson J.J. Thomson provided the first provided the first hint that an atom hint that an atom is made of even is made of even smallersmaller particles. particles.

Thomson ModelThomson Model He proposed a He proposed a

model of the atom model of the atom that is sometimes that is sometimes called the “called the “PlumPlum PuddingPudding” model. ” model.

Atoms were made Atoms were made from a positively from a positively chargedcharged substancesubstance with negatively with negatively charged electrons charged electrons scatteredscattered about, like about, like raisins in a pudding.raisins in a pudding.

Thomson ModelThomson ModelThomson studied Thomson studied the the passage passage of an of an electric current electric current through a gas.through a gas.

As the current As the current passed through passed through the gas, it gave off the gas, it gave off rays of rays of negatively negatively charged particles.charged particles.

Thomson ModelThomson Model

This surprised This surprised Thomson, Thomson, because the because the atoms of the gas atoms of the gas were uncharged. were uncharged. Where had the Where had the negative charges negative charges come from?come from?

Where did they come from?

Thomson concluded that the negative charges came from within the atom.

A particle smaller than an atom had to exist.

The atom was divisible!

Thomson called the negatively charged “corpuscles,” today known as electrons.

Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom.

But he could never find them.

Rutherford’s Gold Foil Rutherford’s Gold Foil ExperimentExperiment

In 1908, the English In 1908, the English physicist Ernest physicist Ernest Rutherford was hard Rutherford was hard at work on an at work on an experiment that experiment that seemed to have little seemed to have little to do with unraveling to do with unraveling the mysteries of the the mysteries of the atomic structure.atomic structure.

Rutherford’s experiment Involved firing Rutherford’s experiment Involved firing a stream of tiny a stream of tiny positively chargedpositively charged particles at a thin sheet of particles at a thin sheet of gold foilgold foil (2000 atoms thick)(2000 atoms thick)

MostMost of the positively of the positively charged “bullets” passed charged “bullets” passed right through the gold right through the gold atoms in the sheet of atoms in the sheet of gold gold foilfoil without changing without changing course at all.course at all.

SomeSome of the positively of the positively charged “bullets,” charged “bullets,” however, did bounce however, did bounce away from the gold sheet away from the gold sheet as if they had hit as if they had hit something something solidsolid. He . He knew that positive knew that positive charges charges repelrepel positive positive charges.charges.

This could only mean that the gold atoms in the This could only mean that the gold atoms in the sheet were mostly sheet were mostly open spaceopen space. Atoms were . Atoms were notnot a pudding filled with a positively charged a pudding filled with a positively charged material.material.

Rutherford concluded that an atom had a Rutherford concluded that an atom had a small, small, dense, positively charged centerdense, positively charged center that that repelledrepelled his positively charged “bullets.”his positively charged “bullets.”

He called the center of the atom the “He called the center of the atom the “nucleusnucleus”” The nucleus is The nucleus is tiny tiny compared to the atom as a compared to the atom as a

whole. whole.

RutherfordRutherford

Rutherford reasoned Rutherford reasoned that all of an atom’s that all of an atom’s positively charged positively charged particles were particles were containedcontained in the in the nucleus. The nucleus. The negatively charged negatively charged particles were particles were scatteredscattered outside the outside the nucleus around the nucleus around the atom’s atom’s edgeedge..

Bohr ModelBohr ModelIn 1913, the Danish In 1913, the Danish scientist Niels Bohr scientist Niels Bohr

proposed an proposed an improvement. In his improvement. In his model, he placed model, he placed each electron in a each electron in a

specificspecific energy energy level.level.

Bohr ModelBohr ModelAccording to Bohr’s According to Bohr’s

atomic model, electrons atomic model, electrons move in definite move in definite orbitsorbits

around the nucleus, much around the nucleus, much like planets circle the sun. like planets circle the sun.

These orbits, or energy These orbits, or energy levelslevels, are located at , are located at

certaincertain distances from the distances from the nucleus.nucleus.

How exactly are the particles How exactly are the particles arranged?arranged?

Bohr Model of the atom:Bohr Model of the atom:Reviewers think this could lead to misconceptions!Reviewers think this could lead to misconceptions!

All of the protons and the neutrons

The 1st ring can hold up to 2 e-

The 2nd ring can hold up to 8 e-

The 3rd ring can hold up to 18 e-

The 4th ring and any after can hold up to 32 e-

What does carbon look like?What does carbon look like?

Mass # = 12 Mass # = 12 atomic # atomic # = 6= 6

pp++ = 6 = 6 nnoo = 6 = 6 ee-- = 6 = 6

6 p and 6 n live in the nucleus

Wave Model

The Wave ModelThe Wave Model Today’s atomic Today’s atomic

model is based on model is based on the principles of the principles of wavewave mechanicsmechanics..

According to the According to the theory of wave theory of wave mechanics, electrons mechanics, electrons do not movedo not move about about an atom in a an atom in a definite definite path,path, like the planets like the planets around the sun.around the sun.

The Wave ModelThe Wave Model

In fact, it is In fact, it is impossibleimpossible to determine the exact to determine the exact location of an electron. The location of an electron. The probableprobable location of location of an electron is based on how much an electron is based on how much energyenergy the the electron has.electron has.

According to the modern atomic model, an atom According to the modern atomic model, an atom has a has a small positively charged nucleussmall positively charged nucleus surrounded by a large region in which there are surrounded by a large region in which there are enough electrons to make an atom neutral.enough electrons to make an atom neutral.

Electron Cloud:Electron Cloud: A space in which A space in which

electrons are likely to be electrons are likely to be found.found.

Electrons Electrons whirlwhirl about the about the nucleus billions of times nucleus billions of times in one secondin one second

They are not moving They are not moving around in around in randomrandom patterns.patterns.

Location of electrons Location of electrons depends upon how much depends upon how much energyenergy the electron has. the electron has.

Electron Cloud:Electron Cloud:

Depending on their energy they are locked into a Depending on their energy they are locked into a certain area in the cloud.certain area in the cloud.

Electrons with the Electrons with the lowestlowest energy are found in energy are found in the energy level the energy level closestclosest to the nucleus to the nucleus

Electrons with the Electrons with the highesthighest energy are found energy are found in the in the outermostoutermost energy levels, farther from energy levels, farther from the nucleus.the nucleus.

Outermost electrons are called Outermost electrons are called valence valence electrons.electrons.

All elements want 8 e- in there outer shell. This All elements want 8 e- in there outer shell. This makes them the most stable.makes them the most stable.

The regions in a atom that electrons are The regions in a atom that electrons are likely to be found are called orbitals.likely to be found are called orbitals.

The four different orbitals are called s, p, The four different orbitals are called s, p, d, and f orbitals.d, and f orbitals.

s orbitals are the simplest orbitals. They s orbitals are the simplest orbitals. They are sphere shaped, they hold 2 electrons.are sphere shaped, they hold 2 electrons.

A A pp orbital is dumbbell in shape and can orbital is dumbbell in shape and can be oriented three ways in space.be oriented three ways in space.

Because each Because each pp orbital can hold two orbital can hold two electrons, the three orbitals can hold 6 eelectrons, the three orbitals can hold 6 e--..

The The dd and and ff orbitals are much more orbitals are much more complex. Five possible d orbitals and 7 complex. Five possible d orbitals and 7 possible possible ff orbitals. An orbitals. An ff orbital has the orbital has the greatest energy.greatest energy.

IsotopesIsotopes

An isotope is an element that has the An isotope is an element that has the same number of protons but a different same number of protons but a different number of neutrons.number of neutrons.

They feature some of the same chemical They feature some of the same chemical properties of the element.properties of the element.

Isotopes of an element vary in mass Isotopes of an element vary in mass because their numbers of neutrons differ.because their numbers of neutrons differ.

Isotopes of HydrogenIsotopes of Hydrogen

Isotopes of Hydrogen (Cont.)Isotopes of Hydrogen (Cont.)

Hydrogen is present on Earth and the sun. Hydrogen is present on Earth and the sun. In both places, protium is most common.In both places, protium is most common.

Only a small fraction of hydrogen found on Only a small fraction of hydrogen found on Earth and the sun is deuterium.Earth and the sun is deuterium.

Tritium is an unstable isotope and decays Tritium is an unstable isotope and decays very quickly. It is the least common isotope very quickly. It is the least common isotope of Hydrogen.of Hydrogen.

Calculating NeutronsCalculating Neutrons

When you write an atomic symbol for an When you write an atomic symbol for an isotope of an element you will write the isotope of an element you will write the elements chemical symbol accompanied elements chemical symbol accompanied by the atomic mass of the element.by the atomic mass of the element.

Ex. Uranium-235 (used in nuclear Ex. Uranium-235 (used in nuclear reactors), Cl-20reactors), Cl-20

Lesson 4: Using Moles to Count Lesson 4: Using Moles to Count AtomsAtoms

Counting things is one of the first thing children Counting things is one of the first thing children learn. Can you imagine counting the grains learn. Can you imagine counting the grains of sand along a stretch of beach or stars in of sand along a stretch of beach or stars in

the sky?the sky?

Chemists deal with large numbers of small Chemists deal with large numbers of small particles.particles.

They use a large counting unit, a collection of They use a large counting unit, a collection of very large number of particles. This unit is very large number of particles. This unit is the the molemole..

1 mole = 602 213 670 000 000 000 000 000 1 mole = 602 213 670 000 000 000 000 000 particlesparticles

Or 6.022 x 10Or 6.022 x 102323 particles (MEMORIZE THIS!) particles (MEMORIZE THIS!)

This number is known as This number is known as Avagadro’s Avagadro’s ConstantConstant..

Named in honor of Italian scientist Amedeo Named in honor of Italian scientist Amedeo Avagadro.Avagadro.

Why 6.022 x 10Why 6.022 x 102323? This is the amount of ? This is the amount of atoms in 12.00 g of carbon-12.atoms in 12.00 g of carbon-12.

One mole of gumballs is 6.022 x 10One mole of gumballs is 6.022 x 102323 gumballs. gumballs.One mole of marbles is 6.022 x 10One mole of marbles is 6.022 x 102323 marbles. marbles.One mole of pretzels is ____________ One mole of pretzels is ____________

pretzels.pretzels.

Moles and Grams are RelatedMoles and Grams are RelatedThe mass in grams of 1 mol of a The mass in grams of 1 mol of a

substance is called its molar mass.substance is called its molar mass.The molar mass of 1 mole of carbon is The molar mass of 1 mole of carbon is

12.01 grams.12.01 grams.

1 mole of any element is its atomic mass.1 mole of any element is its atomic mass.

Converting Amount to MassConverting Amount to Mass

Determine the mass in grams of 5.50 mol of Determine the mass in grams of 5.50 mol of iron.iron.

1.1. List the given and unknown values.List the given and unknown values.Given: amount of iron= 5.50 molGiven: amount of iron= 5.50 mol

Molar mass of iron= 55.85 g/mol FeMolar mass of iron= 55.85 g/mol Fe

Unknown: mass of iron= ? g FeUnknown: mass of iron= ? g Fe

So…So…

5.50 mol Fe 5.50 mol Fe 55.85 g Fe 55.85 g Fe = 307 g Fe = 307 g Fe 1 mol Fe1 mol Fe

So…So…What is the mass in grams of each of the What is the mass in grams of each of the

following?following?1.1. 2.50 mol of sulfur 3. 1.80 mol of Ca2.50 mol of sulfur 3. 1.80 mol of Ca2. 1.80 mol of Ca2. 1.80 mol of Ca 4. 3.20 mol of Cu 4. 3.20 mol of Cu

Converting Mass to an AmountConverting Mass to an Amount

Determine the amount of iron present in 352 g Determine the amount of iron present in 352 g of iron.of iron.

Given:Given:Mass of iron = 352 g FeMass of iron = 352 g FeMolar Mass of Iron = 55.85 g/ mol FeMolar Mass of Iron = 55.85 g/ mol Fe

Unknown: Unknown: Amount of iron = ? Mol FeAmount of iron = ? Mol Fe