History of the Development of the Atomic Model, Part 1

AS Aim #1Where did the idea of the atom come from?

Atomic Model of the Atom • Models help us describe several

things about an atom:– ____________ – what its

made of– __________________ – lets us determine

how atoms interact with each other• We will look at several models of the atom

that build upon previous models• The modern model of the atom is based

on the work of many scientists, not just one!

Early Greek Theories

• Democritus • 400 B.C.• His theory:

– everything is composed of "atoms", which are physically ___________________________;

– are always ________________; – come in there are an __________________

of types, variety, and shapes• Based his theory on _____________________

Early Greek Theories• Aristotle• 350 B.C• Presented a modified earlier theory

that matter was made of four “elements”; ______, ____, ______, and ________

• Based his theory on reason, ______________• But…• ____________________!• __________________________ must be done

to ensure theories hold up under scrutiny!

John Dalton’s Atomic Theory of the Atom• Early 1800’s English teacher John

Dalton – proposed a modern atomic

model of structure ________ _______________________ _______________________

– Described elements as being composed of particles called _______________________

– _______________________ to a given element

Components of Dalton’s Model• All matter is __________________

• Atoms of an element _________________

• Each element has ___________________

4. Atoms of different elements combine in __________________ to form compounds.

• Think of H20 vs H2O2

5. Atoms are __________________________• 2 H2 +O2 2 H2O

Dalton’s Theory accounts for:• The Law of Conservation of Mass

– Mass cannot be ____________________– Hydrogen + Oxygen = Water– 2 grams + 16 grams = ______________

• The Law of Constant Composition – elements combine in fixed ratios. – 2 hydrogen + 1 oxygen = _______________ – 2 hydrogen + 2 oxygen = _______________

• PROBLEM – no clues in his model as to the

_________________________ of the atom

Cathode Rays and Electrons • By 1897, experiments suggested atoms are

composed of subatomic particles– Subatomic particles - ________________

• British physicist J.J. Thomson– Used a ________________________ and

discovered particles he called ___________– ____________ are

negatively charged – Mass of one electron only

1/1836 of a ________________

The Thomson Atomic Model • “Plum pudding” model

– an atom is a positively charged, jellylike mass with electrons “stuck” in it

• Did not _____________ Dalton’s model

• Built upon Dalton’s model – __________ positive

and negative charges– _________________

to the charges

History of the Development of the Atomic Model, Part 2AS Aim #2 – What is significance of the Gold Foil Experiment?

Ernest Rutherford’s Gold Foil Experiment

• In his experiment, he bombarded (hit) extremely thin gold foil with _____________ – a helium nucleus only (_______________)– has a __________________– _______________________ (more later)

• Based on Thomson’s Theory:– Particles should bounce off the

___________________ or – Particles should stick to the

negative electrons made up of Thomson’s “plums”

• Experimental Results– Some alpha particles _______________ or

__________________– But some particles ____________________

the atom– Why?

• Rutherford’s Conclusion– Most of the mass of the atom is concentrated

in a ________________________________– Electrons are present in the space

________________________________– The typical model of the atom

represented in the media is Rutherford’s model at the right

– So most of the volume of an atom is ____________________

Bohr’s Atomic Model• Rutherford didn’t say where electrons

were __________________• Bohr said that electrons exist in

_________ or _________________• n represents the energy level

– Energy level n = 1 , holds up to ___________– Energy level n = 2 , hold up to ___________– Energy level n = 3 , hold up to ____________– Energy level n = 4 , holds up to ___________

Bohr’s Experiment:– Bohr used hydrogen gas which he heated to

___________________– He analyzed the light patterns using a device

called a ___________________________ which separated the colors of light produced

– In hydrogen, he found four specific

____________

of color

Bohr’s Theory:• Bohr found that electrons moved

from one energy level to another when they gained energy

• They released the energy as light (photons)

• In the lowest levels, or the ground state, to the excited state ____________________ ________________________

• When electrons moved from the excited state back to the ground state, ______________

Bohr’s Theory:• This energy

appears as wavelengths (______________) _______________

• Each element produces its own pattern of

______________ or _________________

• This is because each has different numbers of electrons

Summary of History of the Atomic Model

• Democritus – came up with the word _____• Dalton – his original atom had no ________,

neutrons, or ________ in it• Thompson – used _______________ tubes

to discover electrons and their charge• Rutherford – his experiment shot

_____________ at a piece of ____________• Bohr – used excited hydrogen atoms to

produce ___________ in various colors, and proved electrons existed in different energy levels

History of the Development of the Atomic Model, Part 3

AS Aim #3:Where does the Modern Model of the Atom place electrons?

Modern Atomic or Wave Mechanical Model

• Bohr’s shell model at the right is not quite right either!

• Electrons actually exist in ________________________ around the nucleus, not in orbits like planets around the Sun

• As per the Modern Atomic Model

• Also known as the Wave Mechanical Model of the Atom

Modern Atomic or Wave Mechanical Model

• These locations are based on where they are most likely found, ________________

• We call this arrangement an _____________________

• ______________ are a three dimensional representation of principal energy levels

• Each energy level (n) contains smaller areas called ____________

• In the Periodic Table, each block represents a __________________ with electrons

• This is what gives the Periodic Table its _____________________

• There are _______________• each labeled “s”, “p”, “d”, and “f”

• Sublevels are further broken down into areas called ____________

• Each orbital only holds two (2) electrons each maximum and has a _____________

Sublevel Number of orbitals

Shape of orbitals

Maximum # of electrons

s 1 Single round sphere

p 3 Three dumbbell shapes

d 5 Five dumbbell shapes

f 7 Seven dumbbell shapes

• Orbital shapes affect– how the Periodic Table _____________– how _______________ with each other

• Look at the Periodic Table• Count the elements across

each block. How many elements are there in each?

• s sublevel block = ____• p sublevel block = ____• d sublevel block = ____• f sublevel block = ____• Each ____________________ in the Periodic

Table represents 1 more electron being added

• Simplified Electron Configurations:– ____________________ surround an atom – ____________________ are in each energy

level– ____________________ they exist in

Atomic mass

Atomic Number Symbol

Electron Configuration (2 e- in 1st level, 4 e- in 2nd level)

12.011 - 4 +2 +4

62-4

C

Basic Electron Configuration• Electrons fill the lowest energy levels first

(_______________)• The electron configuration is a “code” for

showing _______________ around an atom

Element 1st Shell

2nd Shell

3rd Shell

4th Shell

Electron Config

He 2 2Na 2 8 1 2-8-1Br 2 8 18 7 2-8-18-7Ca 2 8 8 2 2-8-8-2

The Octet Rule of Electron Configs• Why is calcium’s 3rd shell not filled?• It should take up to __________ in the 3rd shell

• The Octet Rule – no atom can have more than 8 electrons in the

_____________________ energy level– If more than 8 electrons in an energy level occurs,

we push two up to the next energy level

Element 1st Shell

2nd Shell

3rd Shell

4th Shell

Electron Config

Ca 2 8 8 2 2-8-8-2

The Octet Rule of Electron Configs• Having 8 electrons in the valence shell also

makes the ___________• This occurs in the last column of the Periodic

Table, a group of elements called Noble _____• Very _____________ with other elements

Element 1st Shell

2nd Shell

3rd Shell

4th Shell

Electron Config

Ne 2 8 - - 2-8Ar 2 8 8 - 2-8-8Kr 2 8 18 8 2-8-18-8

Excited State Electron Configurations• Excited state electrons can be shown by not

filling the _________________• Electrons have ___________ to higher shells

ElementGround state

electron configuration

Excited state electron

configurationsHe 2 1-1, 1-0-1Na 2-8-1 2-7-2, 2-7-1-1Br 2-8-18-7 2-8-18-6-1, 2-8-17-8Ca 2-8-8-2 2-8-7-3, 2-8-8-1-1

• Fill in the chart below for each element’s ground state electron configuration and one excited state configuration:

Element Ground state configuration

Excited state configuration

KMgOSNPAr

Atoms + Electrons = Ions

AS Aim #4 – Why are most elements “wannabees”?

HAIL THE MIGHTY VALENCE ELECTRONS!• Most of chemistry is really all about electrons

and where they go and stay• All elements in the Periodic Table are

“__________________________” (Group 18)– If an atom can gain or lose electrons, it can have the

electron configuration as the noble gases• These elements become stable when they form

_________:– a gain or loss of electrons gives an _____________ – a __________ electrons creates a negative ion– a __________ electrons creates a positive ion

HAIL THE MIGHTY VALENCE ELECTRONS!• Ions are atoms with a charge, or an unequal

number of protons and electrons• What is the charge on a proton? ______• What is the charge on an electron? ______• What is the charge on each of the following

atoms:– 5 protons and 5 electrons = ______________– 5 protons and 4 electrons = ______________– 5 protons and 6 electrons = ______________– 19 protons and 21 electrons = ______________

HAIL THE MIGHTY VALENCE ELECTRONS!• Ions of opposite charge can thus form

compounds• Positive ions ________________ negative ions

(___________________!)• In compounds, as in atoms, charges must add

_________________• Therefore:

– A +1 ion bonds with a -1 ion (+1 + -1 = ____)– A +2 ion bonds with a -2 ion (+2 +-2 = _____)– A +2 ion bonds with two -1 ions (+2 +(-1x2))= ___)

• Each of the atoms below want to be ions with a stable electron configuration of eight

• Determine how many electrons are gained or lost• Write the new electron configuration

ElementElectron Config of

atom

Gained or lost e-

Electron Config of ion

K 2-8-8-1 1 lost 2-8-8Mg 2-8-2 2 lost 2-8O 2-6 2 gained 2-8N 2-5 3 gained 2-8Li 2-1 1 lost 2

Lewis Electron-Dot Diagrams• Another way to represent _____________• Lewis Dot Diagrams shows the number of

______________________• Procedure

– Write the symbol first– Use the Periodic Table to find the number of

valence (outermost) electrons– Place two dots to represent the first electrons

on top– Place the rest evenly around the atom

Lewis Electron-Dot Diagrams• Example: draw the Lewis Dot for

chlorine and for sodium

• Notice: chlorine __________ to be like a noble gas, sodium ________________

Name, Symbols, and Atomic Numbers

AS Aim #5 – What does a chemical symbol tell us about an element?

Identifying Elements – Names, Symbols, and Atomic Numbers

• Every element (as well as its atoms) is associated with three unique identifiers– Names– Symbols– Atomic numbers (number of protons in an atom)

– obtained from the periodic tableElement

NameElement Symbol

Element Atomic Number

Hydrogen H 1Sodium Na 11

Gold Au 79

Identifying Elements – Names, Symbols, and Atomic Numbers• Names

– are based on – _______– like Einsteinium– ________ – like Francium– ________________ - like

chlorine (comes from the Greek work chloros, or “yellow green”)

Identifying Elements – Names, Symbols, and Atomic NumbersSymbols• Each element with permanent

names have unique letters associated with them

– First letter ____________capitalized– Second letter ______________capitalized

• New elements have three letter symbols __________________ to them

• Some elements originally had ___________• Example – Mercury, or hydragyras (Hg)

Identifying Elements – Names, Symbols, and Atomic Numbers

• Give either the name or the symbol of each (you may need to use Table S to do this!)

Name Symbol Name Symbol

Nickel Ni Magnesium Mg

Tungsten W Radium Ra

Radon Rn Uranium U

Bromine Br Arsenic As

Identifying Elements – Names, Symbols, and Atomic Numbers

• Atomic number - this represents the number of ____________ in the atom’s ______________

• Each element has its own atomic number• Therefore, • the _______________ gives you the element• Examples:

Atomic number = 2 = 2 protons = _______Atomic number = 8 = 8 protons = _______Atomic number = 79 = 79 protons = _____

Identifying Elements – Names, Symbols, and Atomic Numbers

• Give the name of the element based on the atomic number (use Table S and the Periodic Table)

Atomic #

Name Atomic #

Name

4 Beryllium 25 Manganese

8 Oxygen 50 Tin

12 Magnesium 75 Rhenium

16 Sulfur 100 Fermium

Identifying Elements – Names, Symbols, and Atomic Numbers• The Atomic Number also gives us the number of

electrons in an atom• Remember,

– Protons = charge of _____– Electrons = charge of ______– Neutrons = charge of ___________– ATOMS are always electrically ___________

(charge = 0)– Therefore, in an atom,

the # of __________= the # of ___________but not the number of neutrons (that changes!)

Masses and Isotopes

AS Aim #6:What makes something an isotope?

Using the Periodic Table to find Names, Symbols, and Atomic Numbers

• The Periodic Table of the elements is the master chart of chemistry

• Contains various pieces of information including:

Atomic mass Oxidation (Total protons+neutrons) states

Atomic Number Symbol(number of protons, only)

Electron Configuration (arrangement of electrons in energy levels)

12.011 - 4 +2 +4

62-4

C

Using the Periodic Table to find Names, Symbols, and Atomic Numbers

• Determine the following information for each element from the Periodic Table:

Name Symbol Atomic Number

Atomic Mass

Electron Config

Hydrogen H 1 1.0079 1Boron B 5 10.81 2-3

Chlorine Cl 17 35.45 2-8-7Argon Ar 18 39.95 2-8-8

Calcium Ca 20 40.08 2-8-8-2

Isotopes, Mass Numbers, and Neutrons • Mass number – a measure of the number of

____________________________ in an atom• Why not electrons too?• _________________________!!!• Masses of subatomic particles are measured in

units called _____________________ or amu’s– Mass of 1 neutron = 1 amu– Mass of 1 proton = 1 amu– Mass of 1 electron = 0.0005 amu

• Therefore, Mass number = # of protons + # of neutrons

Isotopes, Mass Numbers, and Neutrons • Does this mean that atoms of the same

element all have the same mass numbers?• ________! • Atoms of the same element are actually a bit

different• We call them ISOTOPES

– All atoms of an element have the ___________________ (# of protons)

– But atoms of the same element can have ____________________ (different #s of neutrons)

Isotopes, Mass Numbers, and Neutrons

• Examples of Isotopes - hydrogen – There are three forms of hydrogen isotope

Form of Hydrogen

Isotope

Atomic Number

(# of protons)

Mass Number (# of protons + neutrons)

# of Neutrons

Protium 1 1 0Deuterium 1 2 1

Tritium 1 3 2

Neutrons, Isotopes, and Mass Numbers

• Isotopes of hydrogen

Isotopes, Mass Numbers, and Neutrons • Question 1 - an atom has an atomic number of 6,

and a mass number of 12 amu. – What element is it?

______________– How many protons does it have?

______________– How many neutrons does it have?

mass of 12 – 6 protons = 6 neutrons– How many electrons does it have?

________________________________– IMPORTANT! 1 amu = 1/12 the mass of a

typical carbon atom

Isotopes, Mass Numbers, and Neutrons • Question 2 - an atom has an atomic number of 6,

and a mass number of 14 amu. – What element is it?

____________– How many protons does it have?

____________– How many neutrons does it have?

_______________________________– How many electrons does it have?

_______________________________– This is an ISOTOPE of carbon

Neutrons, Isotopes, and Mass Numbers

• Isotopes of carbon

Representing isotopesIsotopes can be represented in several ways• As the element with it _______________

– Ex: carbon-12, carbon-13, carbon-14

• As the element’s symbol with its ________________– Ex: C-12, C-13, C-14

• As the symbol with both the __________ and the atomic number represented

Neutrons, Isotopes, and Mass Numbers

• Problem – how many protons, neutrons, and electrons are contained in a neutral atom of uranium-238, if the atomic number of uranium is 92?

• Mass number 238 = _______• Protons 92 = _______• Electrons 92 = ___ = ___• Neutrons 146 = _____________

- _____________

Average Atomic Masses

AS Aim #7: Why do atomic mass numbers contain decimals?

Calculating Grade Averages

• You are in the class from H… the teacher has decided that your grade for the quarter will be based on the following weighting:– Exams 60%– Homeworks 30%– Labs 10%

• You score 50% average on your exams, a 70% average on your homework, and an 90% average on your labs.

• Do you pass the course the first quarter?

Calculating Grade Averages

• If the teacher averaged the 3 grades, you would simply add your 3 grades and divide by 3

(50 + 70 + 90 ) / 3 = ___________= you pass and your family is happy!

• BUT = the grade is weighted, so:– Exams 60% x 50% avg = – Homeworks 30% x 70% avg = – Labs 10% x 100% avg = ____– The total comes out to be

• You fail, and now you get to attend extra help FOREVER

Calculating Grade Averages• Problem #1 - Evil Mr. Foley decides your

second quarter exams will be 80% of your Test grade, HW will be 10%, and Labs will be 10%. If you score a 60 avg on exams, an 80 avg on labs, and a 100 avg on labs, do you pass?

Calculating Grade Averages• Problem #2 – Mr. Foley’s good twin decides in his

class that the weighting will be quite different. For the second quarter, exams will be 50% of your grade, HW will be 30%, and Labs will be 20%. If you still score a 60 avg on exams, an 80 avg on homework, and a 100 avg on labs, do you pass?

Calculating Atomic Weights• Determining the atomic weights of elements is the

same• _______________________________________

_______________________________________• So we need to calculate the atomic weight based

_______________________________• Example 1 – a sample of hydrogen isotopes:

– Hydrogen-1 has an abundance of 95% – Hydrogen-2 has an abundance of 3%– Hydrogen-3 has an abundance of 2%

• What is the average atomic mass of this sample?

Calculating Atomic Weights• Hydrogen-1 has an abundance of 95%• Hydrogen-2 has an abundance of 3%• Hydrogen-3 has an abundance of 2%

Hydrogen 1 = 1 amu x 95% = Hydrogen 2 = 2 amu x 3% = Hydrogen 3 = 3 amu x 2% = ______

Calculating Atomic Weights• Example 2: A sample of sulfur has the

following isotopes in it– Sulfur-30 with an abundance of 60% – Sulfur-32 with an abundance of 30%– Sulfur-34 with an abundance of 10%

• What is the average atomic mass of this sulfur sample?Sulfur-30 = 30 amu x 60% = Sulfur-32 = 32 amu x 30% = Sulfur-34 = 34 amu x 10% = ________