Atomic Structure

Mrs. Daniels Chemistry .2Mrs. Daniels Chemistry .2September 2002 Revised August 2006September 2002 Revised August 2006

IN YOUR JOURNALS…

Describe what you think atoms are made of.Describe what you think atoms are made of.

Can you see an atom with your naked eye Can you see an atom with your naked eye or under a microscope?or under a microscope?

Draw a picture of a simple atom and its Draw a picture of a simple atom and its components.components.

Dalton’s Atomic Theory

1.1. All elements are composed of tiny indivisible All elements are composed of tiny indivisible particles called atomsparticles called atoms

2.2. Atoms of the same element are identical to each Atoms of the same element are identical to each other & are different from those of other other & are different from those of other elementselements

3.3. Atoms can physically mix together or Atoms can physically mix together or chemically combine in whole number ratios to chemically combine in whole number ratios to form compounds.form compounds.

4.4. Chemical reactions occur when atoms are Chemical reactions occur when atoms are separated, joined, or rearranged.separated, joined, or rearranged.

How BIG or how small is an atom?

Is a penny big or small?Is a penny big or small? Imagine grinding up the penny into copper Imagine grinding up the penny into copper

dust. Is each grain of copper big or small?dust. Is each grain of copper big or small? A pure copper penny contains A pure copper penny contains

approximately 2.4 x 10approximately 2.4 x 102222 individual copper individual copper atomsatoms

Can you imagine dividing the penny into Can you imagine dividing the penny into 24,000,000,000,000,000,000,000 different 24,000,000,000,000,000,000,000 different parts?parts?

“Cutting it down to size activity”

Pair up with the person sitting next to youPair up with the person sitting next to you You and your partner will be given two items: a You and your partner will be given two items: a

pair of scissors and a piece of paperpair of scissors and a piece of paper Your task: predict how many times you and Your task: predict how many times you and

your partner can cut this piece of paper in half your partner can cut this piece of paper in half with the scissorswith the scissors

Each time, discard (set aside and we’ll discard at Each time, discard (set aside and we’ll discard at the end) one half of the paper you’ve cut and the end) one half of the paper you’ve cut and continue on with one piececontinue on with one piece

“Cutting it down to size activity”

How many times were you able to cut the paper How many times were you able to cut the paper in half?in half?

Which pair was able to make the most cuts?Which pair was able to make the most cuts? How many times would you have to divide this How many times would you have to divide this

original 8 1/2 x 11” piece of paper in order to original 8 1/2 x 11” piece of paper in order to get it to be the width of one atom?get it to be the width of one atom?

3131

Atomic Structure

First of all, an atom has no overall electric First of all, an atom has no overall electric charge.charge.

Secondly, we know that an equal number of Secondly, we know that an equal number of negative and positive particles combine to negative and positive particles combine to form a neutral particleform a neutral particle

Keeping this in mind, let’s look at three Keeping this in mind, let’s look at three subatomic particlessubatomic particles..

Atomic Structure

Proton (pProton (p++)):: A positively charged A positively charged particle found in the central core of an atom particle found in the central core of an atom (called the nucleus)(called the nucleus)

Neutron (nNeutron (n00)):: A neutral particle A neutral particle found in the nucleus of an atomfound in the nucleus of an atom

Electron (eElectron (e--)):: A tiny negatively A tiny negatively charged particle found outside of the atomic charged particle found outside of the atomic nucleusnucleus

Atomic Structure

The mass of a proton and a neutron is The mass of a proton and a neutron is relatively equalrelatively equal

However, the electron has a mass equal to However, the electron has a mass equal to 1/1840 of a proton1/1840 of a proton

Which subatomic particles do you think Which subatomic particles do you think take up the most space in the atom?take up the most space in the atom?

Atomic Structure

If we can’t see these subatomic particles, If we can’t see these subatomic particles, how do we know they exist?how do we know they exist?

Before we answer that…

The atoms we’re discussing each have a The atoms we’re discussing each have a representative symbol as you should recall.representative symbol as you should recall.

See how many of these elements you can See how many of these elements you can “discover” in the symbol recognition “discover” in the symbol recognition worksheet.worksheet.

Homework tonight:Homework tonight: Read pages 55-61Read pages 55-61

J.J. Thomson’s Cathode Ray Tube

1897 was a big year for J.J…. He discovered the 1897 was a big year for J.J…. He discovered the electron.electron.

Thomson passed electric current through gases Thomson passed electric current through gases under low pressure in a sealed glass tubeunder low pressure in a sealed glass tube

At one end of the glass tube was an electrode with a At one end of the glass tube was an electrode with a positive charge (anode)positive charge (anode) and at the other end was a and at the other end was a negative electrode (cathode)negative electrode (cathode)

When electricity was passed through, a glowing When electricity was passed through, a glowing beam formed between the cathode and the anode. beam formed between the cathode and the anode. This beam was then called a This beam was then called a cathode raycathode ray..

J.J. Thomson’s Cathode Ray Tube

Thomson found that the cathode ray was Thomson found that the cathode ray was attracted to a positively charged metal plateattracted to a positively charged metal plate

Knowing that opposites attract, he Knowing that opposites attract, he concluded that the beam (cathode ray) is concluded that the beam (cathode ray) is made up of tiny negatively charged made up of tiny negatively charged particles moving at high speedparticles moving at high speed

These particles were called These particles were called electronselectrons

Other Scientists MillikanMillikan:: measured the measured the charge of an charge of an

electronelectron MoseleyMoseley:: used an X-ray to determine the used an X-ray to determine the

number of protonsnumber of protons in an atom in an atom Rutherford:Rutherford: used a used a gold foil experimentgold foil experiment to to

determine that most of the atom is empty space determine that most of the atom is empty space and the tiny center of the atom is positively and the tiny center of the atom is positively chargedcharged

ChadwickChadwick:: demonstrated the existence of demonstrated the existence of neutronsneutrons

Organization of the Atom

The protons and neutrons are tightly packed The protons and neutrons are tightly packed in a central core called the nucleusin a central core called the nucleus

If an atom were the size of a football If an atom were the size of a football stadium, the nucleus would be a tiny marble stadium, the nucleus would be a tiny marble sitting in the center of itsitting in the center of it

The electrons are found in different layers The electrons are found in different layers (energy levels) of a “cloud” around the (energy levels) of a “cloud” around the nucleusnucleus

Atomic # & Mass # Elements differ because of the number of Elements differ because of the number of

protons they haveprotons they have The Atomic NumberThe Atomic Number is the number of is the number of

protonsprotons The number of electrons in an atom must The number of electrons in an atom must

equal the number of protons in order for the equal the number of protons in order for the atom to be neutralatom to be neutral

The Mass NumberThe Mass Number is the whole number of is the whole number of protons plus neutrons in an atomprotons plus neutrons in an atom

Atomic # & Mass #

O16

8

Mass Number

AtomicNumber

ChemicalSymbol

Mass # vs. Atomic Mass

Ne20.18

10

Atomic mass

AtomicNumber

ChemicalSymbol

Isotopes

Isotopes of an atom occur when the number Isotopes of an atom occur when the number of neutrons changesof neutrons changes

Isotopes have the same chemical properties Isotopes have the same chemical properties as the original atom because the charged as the original atom because the charged particles remain the sameparticles remain the same

Atomic Mass A weighted average mass of the atoms in a A weighted average mass of the atoms in a

naturally occurring sample of an element is naturally occurring sample of an element is called the called the Atomic MassAtomic Mass

This number represents the mass as well as This number represents the mass as well as the relative abundance of each isotopethe relative abundance of each isotope

Since atoms are so small, grams are not Since atoms are so small, grams are not typically used as units of masstypically used as units of mass

Instead, an Instead, an Atomic Mass UnitAtomic Mass Unit is used is used (mathematically defined as 1/12(mathematically defined as 1/12 thth of the of the mass of Carbon-12.)mass of Carbon-12.)

Bell Work Calculate this student’s grade if the class is Calculate this student’s grade if the class is

weighted as follows:weighted as follows: Tests = 75%Tests = 75% Homework = 5%Homework = 5% Lab = 10%Lab = 10% Final exam = 10%Final exam = 10%

Test scores: 89, 84, 72, 90Test scores: 89, 84, 72, 90

Lab :Lab : 99, 100, 98, 99, 94, 97 99, 100, 98, 99, 94, 97

Homework : 92, 93, 96, 98, 105, 94Homework : 92, 93, 96, 98, 105, 94

Final exam : 90Final exam : 90

Bell Work Calculate this student’s grade if the class is Calculate this student’s grade if the class is

weighted as follows:weighted as follows: Tests = 75%Tests = 75% Homework = 5%Homework = 5% Lab = 10%Lab = 10% Final exam = 10%Final exam = 10%

Test scores: 89, 84, 72, 90 = 335/4 = 83.75%Test scores: 89, 84, 72, 90 = 335/4 = 83.75%

Lab :Lab : 99, 100, 98, 99, 94, 97 = 587/6= 99, 100, 98, 99, 94, 97 = 587/6= 97.8%97.8%

Homework : 92, 93, 96, 98, 105, 94 = 578/6= 96.3%Homework : 92, 93, 96, 98, 105, 94 = 578/6= 96.3%

Final exam : 90%Final exam : 90%

83.75(.75) + 97.8(.10) + 96.3(.05) + 90(.10) = 83.75(.75) + 97.8(.10) + 96.3(.05) + 90(.10) =

86.4% 86.4% BB

Bell Work Now if this teacher did NOT weight grades, Now if this teacher did NOT weight grades,

what would this student’s grade be?what would this student’s grade be?

Test scores:Test scores: 89, 84, 72, 9089, 84, 72, 90Lab :Lab : 99, 100, 98, 99, 94, 9799, 100, 98, 99, 94, 97Homework :Homework : 92, 93, 96, 98, 105, 9492, 93, 96, 98, 105, 94Final exam :Final exam : 9090

1590/1700 = 93.5% 1590/1700 = 93.5% A… A…very differentvery different

Periodic Table of Elements

What do you think of when you hear the What do you think of when you hear the word “periodic”?word “periodic”?

Periodic actually means: occurring on a Periodic actually means: occurring on a regular basisregular basis

There are certain There are certain trendstrends that exist on the that exist on the periodic table that are consistentperiodic table that are consistent

Periodic Table of Elements

A horizontal row across the periodic table A horizontal row across the periodic table is called a period.is called a period.

When you read across the page, you When you read across the page, you eventually come the end of a sentence. At eventually come the end of a sentence. At the end of a sentence is a the end of a sentence is a period.period.

A vertical column on the periodic table is A vertical column on the periodic table is called a called a family or group.family or group.

Alkali Metals

Group/Family I is called the Group/Family I is called the Alkali MetalsAlkali Metals

Hydrogen Hydrogen is not included in this groupis not included in this groupIt is in a group of its ownIt is in a group of its own

This family shares certain This family shares certain characteristics: characteristics: react vigorously with react vigorously with water, are metals, and have 1 e- in water, are metals, and have 1 e- in their outermost shelltheir outermost shell

Li

Fr

Na

Cs

K

Rb

Alkaline Earth Metals

The alkaline earth metals are all The alkaline earth metals are all metals and all have 2 e- in their metals and all have 2 e- in their outermost shelloutermost shell

The second family from the left The second family from the left of the periodic tableof the periodic table

Be

Ra

Mg

Ba

Ca

Sr

Transition Metals

The transition metals are located in the The transition metals are located in the center of the periodic table.center of the periodic table.

They vary in their number of electrons, They vary in their number of electrons, however, they all share in the common however, they all share in the common properties of metals.properties of metals.

~80% of all of the elements are metals~80% of all of the elements are metals The inner transition metals are referred to as The inner transition metals are referred to as

the rare earth elements. These are the two the rare earth elements. These are the two rows found at the bottom of the periodic rows found at the bottom of the periodic table table

Metalloids

Along the zigzag borders are Along the zigzag borders are the metalloidsthe metalloids

These share some properties These share some properties of metals (some of the time)of metals (some of the time)

Aluminum is an exception: it Aluminum is an exception: it is a metalis a metal

Non-metals

In the upper right hand corner of the In the upper right hand corner of the periodic table are the non-metalsperiodic table are the non-metals

Typically non-lustrous and are poor Typically non-lustrous and are poor conductors of electricityconductors of electricity

Halogens (group 7): include chlorine and Halogens (group 7): include chlorine and brominebromine

Noble Gases (group 8): Undergo few or no Noble Gases (group 8): Undergo few or no chemical reactionschemical reactions

Puzzle Activity Instructions As a group, you are resonsible for:As a group, you are resonsible for: Drawing each missing piece of your puzzle (be Drawing each missing piece of your puzzle (be

sure to number it) on the white papersure to number it) on the white paper Guess what design or picture is on the piece and Guess what design or picture is on the piece and

then draw and color it.then draw and color it. When you’re finished, give the puzzle to your When you’re finished, give the puzzle to your

instructor. She will give you the puzzle pieces.instructor. She will give you the puzzle pieces. Compare the real pieces to the ones you’ve drawn. Compare the real pieces to the ones you’ve drawn.

Write down ANY differences.Write down ANY differences. In In youryour Journal, what did this activity have to do Journal, what did this activity have to do

with Mendeleev and the first periodic table?with Mendeleev and the first periodic table?

Valence Electrons

The shell or energy level (n) containing the The shell or energy level (n) containing the outermost electrons for an element is called the outermost electrons for an element is called the valence shellvalence shell

The electrons in that shell are called valence The electrons in that shell are called valence electronselectrons

These electrons are the farthest from the atom’s These electrons are the farthest from the atom’s nucleus and are therefore the easiest to removenucleus and are therefore the easiest to remove

How many valence electrons do each of the alkali How many valence electrons do each of the alkali metals have?metals have?

Valence Electrons

The similarity in the # of valence electrons The similarity in the # of valence electrons causes members of the same family to share causes members of the same family to share chemical behaviorschemical behaviors

Hydrogen is so tiny, however that it reacts Hydrogen is so tiny, however that it reacts very differently than other members of its very differently than other members of its familyfamily

How many valence electrons ?

How many valence electrons do each of the How many valence electrons do each of the following have?following have?

NaNa OO CC ClCl BB

Ionization Energy

Some energy is required to remove an Some energy is required to remove an electron from that valence shellelectron from that valence shell

This energy is referred to as the ionization This energy is referred to as the ionization energyenergy

This energy is measured in VoltsThis energy is measured in Volts Valence electrons are much easier to Valence electrons are much easier to

remove than electrons closer to the nucleus remove than electrons closer to the nucleus and are therefore usually the only ones and are therefore usually the only ones capable of being removedcapable of being removed

Octet Rule

We will soon be talking about chemical bondingWe will soon be talking about chemical bonding One important rule to remember is that atoms tend One important rule to remember is that atoms tend

to want 8 electrons in their outermost shellto want 8 electrons in their outermost shell This could mean that they give electrons up, take This could mean that they give electrons up, take

on electrons, or share electrons in order to achieve on electrons, or share electrons in order to achieve this goalthis goal

Hydrogen & Helium are exceptions…they only Hydrogen & Helium are exceptions…they only want 2.want 2.

Energy Levels or Orbits Each orbit around the nucleus has a very Each orbit around the nucleus has a very

specific energy associated with itspecific energy associated with it When an element was treated with heat When an element was treated with heat

or an electric current, where did the or an electric current, where did the energy go?energy go?

The electrons will absorb this energyThe electrons will absorb this energy If each energy level is assigned a specific If each energy level is assigned a specific

amount of energy, what does the electron amount of energy, what does the electron have to do in order to absorb the extra have to do in order to absorb the extra outside energy?outside energy?

Energy Levels or Orbits

It has to jump to the next energy level It has to jump to the next energy level located farther from the nucleuslocated farther from the nucleus

This is now an “excited electron”This is now an “excited electron” Excited electrons are very unstable and Excited electrons are very unstable and

cannot remain in the excited statecannot remain in the excited state They must return to their original orbit or They must return to their original orbit or

“ground state”“ground state”

Energy Levels or Orbits In order for it to return to its ground state, it In order for it to return to its ground state, it

must give off the exact amount of energy it must give off the exact amount of energy it picked up from the outside sourcepicked up from the outside source

When it returns to its ground state, it emits or When it returns to its ground state, it emits or gives off the energy in the form of light and heatgives off the energy in the form of light and heat

The light emitted by excited electrons in atoms The light emitted by excited electrons in atoms is not a continuous spectrum (all the colors) but is not a continuous spectrum (all the colors) but a line spectrum (only certain wavelengths)a line spectrum (only certain wavelengths)

No two elements have the same line spectrumNo two elements have the same line spectrum

Visible Light Spectrum Reminder: Light is a form of energyReminder: Light is a form of energy Review from gradeschool:Review from gradeschool:

ROY G BIVROY G BIV Violet light has higher energy than Violet light has higher energy than

red lightred light There is an inverse relationship There is an inverse relationship

between light wavelengths and between light wavelengths and energyenergy

So as the So as the wavelength wavelength of light gets of light gets larger, the larger, the energyenergy of light gets of light gets smallersmaller

Other atomic models As you may recall…

Before Bohr, there was Thompson and Before Bohr, there was Thompson and RutherfordRutherford

Thompson proposed that an atom was a ball Thompson proposed that an atom was a ball of positive charges which contained several of positive charges which contained several electronselectrons

Rutherford, with his gold foil experiment, Rutherford, with his gold foil experiment, showed that the bulk of the atom’s mass was showed that the bulk of the atom’s mass was concentrated in a small, positively charged concentrated in a small, positively charged region called the nucleusregion called the nucleus

Quantum Mechanical Model Bohr’s model gave rise to the quantum Bohr’s model gave rise to the quantum

mechanical modelmechanical model When Bohr proposed that the energy When Bohr proposed that the energy

required to excite an electron (which was required to excite an electron (which was then later emitted) was “quantized”then later emitted) was “quantized”

There is a specific amount of energy There is a specific amount of energy required in order for an electron to become required in order for an electron to become excited and move to the next energy level…excited and move to the next energy level…

……BUT, each orbit or energy level has its BUT, each orbit or energy level has its own requirements. They are not all the own requirements. They are not all the same.same.

Quantum Mechanical Model Differing from Bohr’s model, the quantum Differing from Bohr’s model, the quantum

mechanical model suggests that the mechanical model suggests that the electrons don’t just follow an exact path electrons don’t just follow an exact path around the nucleus like our planets do around the nucleus like our planets do around the sunaround the sun

Instead, the true location of the electron is Instead, the true location of the electron is uncertain and only a uncertain and only a probabilityprobability of its of its location is mappedlocation is mapped

This idea lends to the analogy of a cloud This idea lends to the analogy of a cloud (the more dense the cloud, the higher the (the more dense the cloud, the higher the probability of finding the electron there)probability of finding the electron there)

Sublevels

Each energy level (n) is made up of one or Each energy level (n) is made up of one or more subshells or energy sublevelsmore subshells or energy sublevels

The number of energy sublevels is the same The number of energy sublevels is the same as the number of the energy level (n)as the number of the energy level (n)

So, the 3So, the 3rdrd energy level has 3 sublevels; the energy level has 3 sublevels; the 55thth energy level has 5 sublevels and so on. energy level has 5 sublevels and so on.

The sublevels are designated s, p, d, and f.The sublevels are designated s, p, d, and f.

Orbitals As you proceed beyond the 3As you proceed beyond the 3rdrd energy level, energy level,

overlapping of sublevels occurs and overlapping of sublevels occurs and becomes more complex as you increase the becomes more complex as you increase the energy level number.energy level number.

The s sublevels have only one orbitalThe s sublevels have only one orbital The p sublevels have 3 orbitalsThe p sublevels have 3 orbitals The d sublevels have 5 orbitalsThe d sublevels have 5 orbitals The f sublevels have 7 orbitalsThe f sublevels have 7 orbitals

Orbitals s orbitals are sphericals orbitals are spherical

p orbitals are dumbbell-shaped with three p orbitals are dumbbell-shaped with three different spatial orientationsdifferent spatial orientations

d orbitals are interesting: 4 of the 5 kinds of d d orbitals are interesting: 4 of the 5 kinds of d orbitals are clover-leafed and the fifth has two orbitals are clover-leafed and the fifth has two opposite nodes with a ring in betweenopposite nodes with a ring in between

f orbitals are too difficult to visualizef orbitals are too difficult to visualize

RULES FOR FILLING ATOMIC ENERGY LEVELS

1.1. Electrons fill up the energy sublevelsElectrons fill up the energy sublevels2.2. The lowest energy sublevel must be completely The lowest energy sublevel must be completely

filled before the next higher sublevel can begin filled before the next higher sublevel can begin to be filled. (Aufbau principle)to be filled. (Aufbau principle)

3.3. Each orbital can hold a maximum number of 2 Each orbital can hold a maximum number of 2 electrons of opposite spin (Pauli exclusion electrons of opposite spin (Pauli exclusion principle)principle)

4.4. Due to their negative charge, electrons repel Due to their negative charge, electrons repel one another. They will not pair up in an orbital one another. They will not pair up in an orbital of any given sublevel until all orbitals in that of any given sublevel until all orbitals in that sublevel have been half-filled. (Hund’s rule)sublevel have been half-filled. (Hund’s rule)

Electron Configuration

There is a pattern that can be used to help you remember There is a pattern that can be used to help you remember which energy sublevel is next in line:which energy sublevel is next in line:

7s7s 7p7p 7d7d 7f7f 7g7g

6s6s 6p6p 6d6d 6f6f 6g6g

5s5s 5p5p 5d5d 5f5f 5g5g

4s4s 4p4p 4d4d 4f4f

3s3s 3p3p 3d3d

2s2s 2p2p

1s1s

g is theoretical and is not used in current electron configurations

Electron Configuration

Remember, the maximum number of Remember, the maximum number of electrons an s sublevel can hold is 2.electrons an s sublevel can hold is 2.

The p = 6 The d = 10 The f = 14The p = 6 The d = 10 The f = 14

There is an easier way to indicate which There is an easier way to indicate which sublevels are filled compared with drawing sublevels are filled compared with drawing out the line diagrams each timeout the line diagrams each time

This is called Electron ConfigurationThis is called Electron Configuration

Electron Configuration Electron configuration is a shorthand way of Electron configuration is a shorthand way of

showing which orbitals of each sublevel are showing which orbitals of each sublevel are filledfilled

When done correctly, the sum of the When done correctly, the sum of the superscripts of all orbitals equals the number of superscripts of all orbitals equals the number of electrons in the atomelectrons in the atom

For example: the electron configuration for For example: the electron configuration for phosphorus isphosphorus is P 1sP 1s222s2s222p2p663s3s223p3p33

Add the superscripts 2+2+6+2+3 =15 e- in PAdd the superscripts 2+2+6+2+3 =15 e- in P

Exceptions to the rule Chromium and Copper have unusual electron Chromium and Copper have unusual electron

configurationsconfigurations They do not follow Aufbau’s energy diagramThey do not follow Aufbau’s energy diagram Write down the electron configuration for CrWrite down the electron configuration for Cr What does it end with?What does it end with? The true electron configuration for Cr is The true electron configuration for Cr is

1s1s222s2s222p2p663s3s223p3p664s4s113d3d55

LikewiseLikewise,, the electron configuration for Cu ends with 3d the electron configuration for Cu ends with 3d10 10

with only 1 electron in the 4s levelwith only 1 electron in the 4s level