atoms unit 3 introduction to the atom history of the atom + + + - - -

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Introduction to the Introduction to the Atom Atom History of the Atom History of the Atom + + + + + + - - - - - -

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Page 1: Atoms Unit 3 Introduction to the Atom History of the Atom + + + - - -

Atoms Unit 3Atoms Unit 3

Introduction to the AtomIntroduction to the AtomHistory of the AtomHistory of the Atom

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Some of the First Discussions Some of the First Discussions about the Atom….about the Atom….

DemocritusDemocritus (400 BC) (400 BC) named the atomnamed the atom, which , which means indivisible, and said it was the means indivisible, and said it was the smallest smallest particleparticle and and could not be broken downcould not be broken down. .

He was pretty much correct in that if you did break the He was pretty much correct in that if you did break the atom down, it wouldn’t be that “element” any more. atom down, it wouldn’t be that “element” any more. But he wasn’t aware that the atom was made up of But he wasn’t aware that the atom was made up of particles.particles.

IN OTHER WORDS:IN OTHER WORDS: Gold is an element. The smallest part Gold is an element. The smallest part of gold that is STILL gold is an atom.of gold that is STILL gold is an atom.

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Greeks Philosophers Continue the Greeks Philosophers Continue the Discussion and DisagreeDiscussion and Disagree

Aristotle (350 BC) believed Aristotle (350 BC) believed matter matter could always be broken down into could always be broken down into smaller and smaller parts. smaller and smaller parts.

And this is true to a certain extent… but eventually And this is true to a certain extent… but eventually you come to the small basic particles that can no you come to the small basic particles that can no longer be broken apart.longer be broken apart.

In other words:In other words: You CAN break an atom of gold You CAN break an atom of gold down into its parts… protons, electrons and down into its parts… protons, electrons and neutrons, however, it wouldn’t be gold anymore. neutrons, however, it wouldn’t be gold anymore.

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Dalton's Atomic TheoryDalton's Atomic Theory

In 1808, John Dalton proposedIn 1808, John Dalton proposed that that elements were composed of atoms & elements were composed of atoms & that only whole numbers of atoms that only whole numbers of atoms can combine to form compoundscan combine to form compounds

His ideas are now called the Atomic His ideas are now called the Atomic Theory of MatterTheory of Matter

Dalton’s Atomic Theory Dalton’s Atomic Theory (1766 - 1844 AD)(1766 - 1844 AD) was was widely accepted but widely accepted but not totally correctnot totally correct

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1.1. All matter is composed of All matter is composed of atoms. atoms. THIS IS TRUETHIS IS TRUE

2.2. Atoms of the same kind Atoms of the same kind of elements are of elements are identical; atoms of identical; atoms of different elements are different elements are different from each different from each other. other. THIS IS PARTLY TRUETHIS IS PARTLY TRUE

ELEMENT2

ELEMENT2

ELEMENT 3

ELEMENT 3

ELEMENT 1

ELEMENT 1

ELEMENT4

ELEMENT4

Dalton’s Atomic TheoryDalton’s Atomic Theory

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3.3. Atoms can’t be Atoms can’t be changed, created, changed, created, or destroyed. or destroyed. THIS IS PARTLY TRUETHIS IS PARTLY TRUE

4.4. You can make You can make compounds out of compounds out of combinations of combinations of different atoms different atoms THIS IS TRUETHIS IS TRUE

5.5. Chemical Chemical reactions are reactions are rearranging or rearranging or recombining recombining atomsatomsTHIS IS TRUETHIS IS TRUE

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Not all of Dalton’s claims were trueNot all of Dalton’s claims were true

Atoms CAN be divided into even smaller Atoms CAN be divided into even smaller particles (Protons, electrons, neutrons) particles (Protons, electrons, neutrons)

Some elements have atoms that have Some elements have atoms that have different masses. (ISOTOPES)different masses. (ISOTOPES)

Atomic TheoryAtomic Theory

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Dalton’s Atomic Theory of Matter has been Dalton’s Atomic Theory of Matter has been modified. modified.

What remains is…What remains is…

1.1. All matter is composed of atomsAll matter is composed of atoms

2.2. Atoms of any one element differ in Atoms of any one element differ in properties from atoms of another elementproperties from atoms of another element

Atomic TheoryAtomic Theory

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In the 1800’s it was determined that atoms are In the 1800’s it was determined that atoms are actually composed of several basic types of actually composed of several basic types of smaller particles smaller particles

It’s the number and arrangement of these It’s the number and arrangement of these particles that determine the atom’s chemical particles that determine the atom’s chemical properties.properties.

A new definition of an atom is the one we use A new definition of an atom is the one we use today: today: The smallest particle of an element The smallest particle of an element that that retains the chemical propertiesretains the chemical properties of that of that original element.original element.

Atomic TheoryAtomic Theory

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Plum Pudding ModelPlum Pudding Model

JJ Thomson’s cathode ray tube JJ Thomson’s cathode ray tube experiment in the late 1800s showed experiment in the late 1800s showed that atoms had smaller parts, called that atoms had smaller parts, called negative corpuscles; he developed the negative corpuscles; he developed the “plum pudding model.”“plum pudding model.”

The plum pudding model The plum pudding model showed showed electronselectrons (the plums) mixed in together (the plums) mixed in together with protonswith protons (the cake batter) (the cake batter)

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Negative particles

embedded in a sphere of

positive plasma-like matter.

THINK… Chocolate Chip

Cookie

Negative particles

embedded in a sphere of

positive plasma-like matter.

THINK… Chocolate Chip

Cookie

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Atomic StructureAtomic Structure

Scientists still didn’t really understand how Scientists still didn’t really understand how the particles were put together in an atom.the particles were put together in an atom.

This was a difficult question to resolve, This was a difficult question to resolve, given how tiny atoms are. They didn’t given how tiny atoms are. They didn’t have GOOGLE to find out the answer!have GOOGLE to find out the answer!

Most thought it likely that the atom resembled Most thought it likely that the atom resembled Thomson’s modelThomson’s model

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Rutherford’s gold foil experimentRutherford’s gold foil experiment

In 1911, Ernest Rutherford showed: In 1911, Ernest Rutherford showed:

1) atoms had a hard, dense, positively 1) atoms had a hard, dense, positively charged nucleus where most of the mass charged nucleus where most of the mass resided. resided.

2) negatively charged electrons outside the 2) negatively charged electrons outside the nucleus, and that the atom was actually nucleus, and that the atom was actually mostly empty spacemostly empty space..

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Rutherford Model (not to proportion)Rutherford Model (not to proportion)

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Bohr Model of the AtomBohr Model of the Atom

Neils Bohr put Neils Bohr put electrons into electrons into different different energy levels energy levels or shells.or shells.

(This model is not (This model is not correct either… correct either… electrons electrons do notdo not travel in orbits or travel in orbits or paths like the paths like the model suggests)model suggests)

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Modern Day TheoryModern Day Theory(Electron Cloud Theory)(Electron Cloud Theory)

The Modern The Modern Theory Theory suggests that suggests that electrons are electrons are located located somewhere in somewhere in a cloud.a cloud.

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Basic and important facts to rememberBasic and important facts to remember: :

1) All atoms contain the same basic 1) All atoms contain the same basic parts parts (protons, neutrons, electrons)(protons, neutrons, electrons)

2) Atoms of different elements have 2) Atoms of different elements have different numbers of protons.different numbers of protons.

The Periodic Table lists atoms in consecutive order The Periodic Table lists atoms in consecutive order by their Atomic Numberby their Atomic Number

The atomic number is directly related to the number The atomic number is directly related to the number of protons in the nucleus of each atom of that of protons in the nucleus of each atom of that elementelement

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Atoms have:

• A nucleus• small, dense part of the atom •consists of protons and neutrons

•An electron cloud• large part of the atom that is empty space except for the electrons that are moving very fast and very randomly around the nucleus Nucleus Electron

Cloud

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The total number of protons & neutrons The total number of protons & neutrons determines the mass of the atomdetermines the mass of the atom

Called the “Mass Number” Called the “Mass Number” (atomic mass is the (atomic mass is the averaged mass of the isotopes and is given on the averaged mass of the isotopes and is given on the periodic table. Simply round the atomic mass to get periodic table. Simply round the atomic mass to get the mass number)the mass number)

A Carbon atom, has 6 protons and 6 A Carbon atom, has 6 protons and 6 neutrons, so its mass number is 12neutrons, so its mass number is 12

If you know the atomic number & mass If you know the atomic number & mass number of an atom of any element, you can number of an atom of any element, you can determine the atom’s composition and the determine the atom’s composition and the number of neutrons.number of neutrons.

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The ProtonThe Proton

The protons are what give the atom its charge (+)The protons are what give the atom its charge (+)

They add mass to the atom as well. Each proton is They add mass to the atom as well. Each proton is equal to one AMU (atomic mass unit)equal to one AMU (atomic mass unit)

The number of protons in an atom determines what The number of protons in an atom determines what element it is. element it is.

The atomic number signifies the number of protonsThe atomic number signifies the number of protons

Protons are held together in the nucleus by the Protons are held together in the nucleus by the “Strong Force” otherwise they would repel each “Strong Force” otherwise they would repel each other.other.

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The NeutronThe Neutron

The neutron adds mass (1 amu) to an atom The neutron adds mass (1 amu) to an atom but has but has NONO charge charge

Atoms of the same elements are identical Atoms of the same elements are identical due to the number of protons, but there can due to the number of protons, but there can be different numbers of neutrons (we call be different numbers of neutrons (we call those isotopes)those isotopes)

To find the number of neutrons, subtract To find the number of neutrons, subtract the atomic number from the mass number.the atomic number from the mass number.

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ElectronsElectrons Electrons have almost no mass, and we DO NOT Electrons have almost no mass, and we DO NOT

count their mass.count their mass.

Located outside the nucleus in the electron cloud Located outside the nucleus in the electron cloud (aka: shells, orbitals, energy levels) moving at (aka: shells, orbitals, energy levels) moving at incredibly high speeds.incredibly high speeds.

Electrons have a negative (-) charge.Electrons have a negative (-) charge.

Electrons found in the outermost shells of the Electrons found in the outermost shells of the atom are responsible for chemical reactions. atom are responsible for chemical reactions. Electrons have different amounts of energy Electrons have different amounts of energy depending what energy level they are at.depending what energy level they are at.

Electrons can be removed and added to atoms Electrons can be removed and added to atoms quite easily, unlike protons.quite easily, unlike protons.

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Subatomic ParticlesSubatomic Particles

ParticleParticle Symbol Symbol Charge Charge RelativeRelativeMassMass

ElectronElectron e e-- 1-1- 0 0

ProtonProton p p++ + + 1 1

NeutronNeutron n n 0 0 1 1

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Location of Subatomic ParticlesLocation of Subatomic Particles

1010-13 -13 cmcm

electronselectrons

protonsprotons

neutronsneutrons

1010-8 -8 cmcm

nucleus

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Atomic NumberAtomic Number

Counts the number Counts the number

of protonsof protons

in an atom and determines in an atom and determines what element it iswhat element it is

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Atomic Number Atomic Number on the Periodic Tableon the Periodic Table

1111

NaNa

Atomic Number

Symbol

The symbol represents the element. RULE: The first letter is always capitalized, and IF

there is a second letter, it is lower case.

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All atoms of an element have All atoms of an element have the same number of protonsthe same number of protons

1111

NaNa11 protons

Sodium

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Atomic Mass on the Periodic TableAtomic Mass on the Periodic Table

1111

NaNa

22.9922.99

Atomic Number

Symbol

Atomic Mass

Atomic mass is the weighted average mass of all the atomic masses

of the isotopes of that atom. That is why there is a decimal.

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Mass NumberMass Number

Counts the number Counts the number

of of

protons and neutronsprotons and neutrons

in an atomin an atom

(note: Atomic Mass is different from Mass Number. (note: Atomic Mass is different from Mass Number. On your periodic table of elements, the atomic mass On your periodic table of elements, the atomic mass

is usually given and you need to round it to the is usually given and you need to round it to the nearest whole number to use to figure Neutrons)nearest whole number to use to figure Neutrons)

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Atomic NotationAtomic Notation

Shows the Shows the mass number and atomic mass number and atomic

numbernumber

Gives the symbol of the elementGives the symbol of the element

mass numbermass number

23 23 NaNa sodium-23sodium-23

atomic numberatomic number 1111

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Number of ElectronsNumber of Electrons

An atom is neutral when no charge is An atom is neutral when no charge is indicated.indicated.

The net charge is zeroThe net charge is zero

Remember: Atomic number = Number of Remember: Atomic number = Number of protonsprotons

and therefore….and therefore….

Number of protons = Number of electrons Number of protons = Number of electrons when the atom is neutral.when the atom is neutral.

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Subatomic Particles Subatomic Particles Showing the P E NShowing the P E N

1616 3131 6565 OO P P Zn Zn

88 1515 3030

8 p8 p++ 15 p15 p++ 30 p30 p++

8 e8 e-- 1515 ee-- 30 e30 e--

8 n8 n 16 n16 n 35 n35 n

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IsotopesIsotopes

Atoms with the same number of Atoms with the same number of

protons, but different numbers of protons, but different numbers of

neutrons. neutrons. Atoms of the same element (same Atoms of the same element (same

atomic number) with different mass atomic number) with different mass

numbersnumbers

Isotopes of chlorineIsotopes of chlorine

3535ClCl 3737ClCl1717 1717

chlorine - 35 chlorine - 37chlorine - 35 chlorine - 37

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Learning Check Learning Check

Naturally occurring carbon consists of Naturally occurring carbon consists of three isotopes, three isotopes, 1212C, C, 1313C, and C, and 1414C. State the C. State the number of protons, neutrons, and number of protons, neutrons, and electrons in each of these carbon atomselectrons in each of these carbon atoms. .

1212CC 1313CC 1414CC 66 6 6 6 6

#p _______ _______ _______ #p _______ _______ _______

#e _______ _______ _______#e _______ _______ _______

#n _______ _______ _______ #n _______ _______ _______

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SolutionSolution

1212CC 1313CC 1414CC 66 6 6 6 6

#p #p 6 6 6 6 6 6

#e #e 6 6 6 6 6 6

#n #n 6 6 7 7 8 8