Atomic StructureAtomic Structure

Topic 1Topic 1

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Atomic - Molecular Atomic - Molecular Theory of MatterTheory of Matter

The The Atomic - Molecular Atomic - Molecular Theory of MatterTheory of Matter

states that all matter states that all matter is composed of small, is composed of small, fast moving particles fast moving particles called atoms. These called atoms. These

atoms can join atoms can join together to form together to form

molecules. molecules.

This theory is really This theory is really thousands of thousands of

individual theories individual theories that provide evidence that provide evidence for the whole theory.for the whole theory.

Where did it all Where did it all begin?begin?

The word “atom” The word “atom” comes from the comes from the

Greek word Greek word ““atomos”atomos” which which

means means indivisibleindivisible..

The idea that all The idea that all matter is made up matter is made up of atoms was first of atoms was first proposed by the proposed by the

Greek philosopher Greek philosopher DemocritusDemocritus in the in the 5th century B.C5th century B.C..

AtomsAtomsThe The smallestsmallest particle of an particle of an element element that that retains the retains the properties properties of that of that element.element.

Dalton’s Atomic Theory (1808)Dalton’s Atomic Theory (1808)

1. Elements are composed of extremely small particles called atoms.

3. Atoms of different elements can combine in simple whole number ratios to form compounds.

4. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.

2.1

2. All atoms of a given element are identical. The atoms of one element are different from those of any other element

8 X2Y16 X 8 Y+

2.1

2

2.1

Electrons, protons & neutronsElectrons, protons & neutrons

Which one of Dalton’s assumptions is Which one of Dalton’s assumptions is wrong?wrong?

ElectronElectron

negatively charged subatomic particlenegatively charged subatomic particle

Sir Joseph J Thomson experimented Sir Joseph J Thomson experimented with cathode rayswith cathode rays

He found (1897) that cathode rays He found (1897) that cathode rays could be deflected by electrically could be deflected by electrically charged plates, towards (+) side platecharged plates, towards (+) side plate

J.J. ThompsonJ.J. Thompson

J.J. Thomson, measured mass/charge of e-

(1906 Nobel Prize in Physics) 2.2

2.2

e- charge = -1.60 x 10-19 C

Thomson’s charge/mass of e- = -1.76 x 108 C/g

e- mass = 9.10 x 10-28 g

Measured mass of e-

(1923 NobelPrize in Physics)

Millikan's Oil Drop Experiment

2.2

(Uranium compound)

2.2

ProtonProton

1840x heavier than an electron1840x heavier than an electron

Approx 1AMU (atomic mass unit)Approx 1AMU (atomic mass unit)

A hydrogen atom stripped of an A hydrogen atom stripped of an electronelectron

(+) charged particle(+) charged particle

NeutronNeutron

Discovered in 1932 by Discovered in 1932 by ChadwickChadwick

No chargeNo charge

Mass is equal to that of a Mass is equal to that of a protonproton

Chadwick’s Experiment (1932)Chadwick’s Experiment (1932)

H atoms - 1 p; He atoms - 2 p

mass He/mass H should = 2

measured mass He/mass H = 4

+ 9Be 1n + 12C + energy

neutron (n) is neutral (charge = 0)

n mass ~ p mass = 1.67 x 10-24 g2.2

Subatomic Particles Subatomic Particles

Particle Mass

(g) Charge

(Coulombs) Charge (units)

Electron (e-) 9.1 x 10-28 -1.6 x 10-19 -1

Proton (p) 1.67 x 10-24 +1.6 x 10-19 +1

Neutron (n) 1.67 x 10-24 0 0

mass p = mass n = 1840 x mass e-

2.2

Structure of the AtomStructure of the Atom

Rutherford discovered the Rutherford discovered the nucleus of the atomnucleus of the atom

The nucleus is composed of The nucleus is composed of protonsprotons and and neutronsneutrons

HISTORYHISTORY OF THE ATOMOF THE ATOM

1910 Ernest Rutherfordoversaw Geiger and Marsden carrying out his

famous experiment.

they fired Helium nuclei at a piece of gold

foil which was only a few atoms thick.

they found that although most of them

passed through. About 1 in 10,000 hit

1910

1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite (+) charge of electron3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)4. TeacherTube - Rutherford\'s experiment

particle velocity ~ 1.4 x 107 m/s(~5% speed of light)

(1908 Nobel Prize in Chemistry)

2.2

NucleusNucleus

(+ ) charge(+ ) charge

Occupies a small volumeOccupies a small volume

Contains protons and neutronsContains protons and neutrons

High densityHigh density

atomic radius ~ 100 pm = 1 x 10-10 m

nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

Rutherford’s Model of the Atom

2.2

Outside the nucleusOutside the nucleus

Electron are found outside Electron are found outside the nucleusthe nucleus

Electrons occupy most of the Electrons occupy most of the volumevolume

Is this really an Atom?Is this really an Atom?

The model above represents The model above represents the most modern version of the most modern version of

the atom. the atom.

(Artist drawing)(Artist drawing)

Many of the models that you Many of the models that you have seen may look like the one have seen may look like the one

below. It shows the parts and below. It shows the parts and structure of the atom. Even structure of the atom. Even

though we do not know what an though we do not know what an atom looks like, scientific atom looks like, scientific models must be based on models must be based on

evidence. evidence.

How can Indirect How can Indirect Evidence be Gathered?Evidence be Gathered?

Click here to visit a lClick here to visit a lab where actual scieab where actual scientific research on atntific research on atoms is conducted.oms is conducted.

Identifying features of AtomsIdentifying features of Atoms

A. Atomic Number (Z)A. Atomic Number (Z)

The The numbernumber of of protonsprotons in the nucleus in the nucleus of the atom of a certain element. of the atom of a certain element. This identifies the element.This identifies the element.

The atom is electrically neutral The atom is electrically neutral therefore it must also have therefore it must also have eight eight electrons around its nucleuselectrons around its nucleus

Period

Group

Alkali M

etal

Noble G

as

Halogen

Alkali E

arth Metal

2.4

Atomic Mass Unit (AMU)Atomic Mass Unit (AMU)

Mass of the pMass of the p++ and n and n00 are very small are very small

1.67 x 101.67 x 10-24-24gg

This unit is called theThis unit is called the Atomic Mass Unit Atomic Mass Unit

The AMU isThe AMU is 1/12 the mass of a 1/12 the mass of a Carbon – 12 atom that contains 6p Carbon – 12 atom that contains 6p and 6nand 6n

Atomic number (Z) = number of protons in nucleus

Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

# OF NEUTRONS = mass number – atomic number

XAZ

H11 H (D)2

1 H (T)31

U23592 U238

92

Mass Number

Atomic NumberElement Symbol

2.3

ISOTOPESISOTOPES

The nuclei of atoms must contain The nuclei of atoms must contain the same # of protons but the same # of protons but

neutrons may varyneutrons may vary

ISOTOPESISOTOPES

Atoms that have same # of p+Atoms that have same # of p+

Different # of neutronsDifferent # of neutrons

Different mass numbersDifferent mass numbers

2.3

How many protons, neutrons, and electrons are in C146 ?

How many protons, neutrons, and electrons are in C116 ?

6 protons, 8 (14 - 6) neutrons, 6 electrons

6 protons, 5 (11 - 6) neutrons, 6 electrons

Do You Understand Isotopes?Isotope Maker

2.3

Atomic Mass CalculationsAtomic Mass CalculationsAtomic MassAtomic Mass

The weighted average of the masses The weighted average of the masses of the isotopes of that element. Most of the isotopes of that element. Most elements occur as elements occur as twotwo or more or more isotopesisotopes in nature in nature

Similar to your class averageSimilar to your class average

An ion is an atom, or group of atoms, that has a net positive or negative charge. An atom that has lost or gained one or more electronscation – ion with a positive charge

If a neutral atom loses one or more electronsit becomes a cation.

anion – ion with a negative chargeIf a neutral atom gains one or more electronsit becomes an anion.

Na 11 protons11 electrons Na+ 11 protons

10 electrons

Cl 17 protons17 electrons Cl-

17 protons18 electrons

2.5

A monatomic ion contains only one atom

A polyatomic ion contains more than one atom

2.5

Na+, Cl-, Ca2+, O2-, Al3+, N3-

OH-, CN-, NH4+, NO3

-

13 protons, 10 (13 – 3) electrons

34 protons, 36 (34 + 2) electrons

Do You Understand Ions?

2.5

How many protons and electrons are in Al2713 ?3+

How many protons and electrons are in Se7834

2- ?

2.5

Some Polyatomic Ions (Table 2.3)Some Polyatomic Ions (Table 2.3)

NH4+ ammonium SO4

2- sulfate

CO32- carbonate SO3

2- sulfite

HCO3- bicarbonate NO3

- nitrate

ClO3- chlorate NO2

- nitrite

Cr2O72-

dichromate SCN- thiocyanate

CrO42- chromate OH- hydroxide

2.7

4S4S

3S3S

2S2S

1S1S

3P3P

2P2P

The Development of Atomic The Development of Atomic ModelsModels

The timeline shoes the development of The timeline shoes the development of atomic models from 1803 to 1911.atomic models from 1803 to 1911.

5.1

Electrons in AtomsElectrons in AtomsDaltonDalton– IndivisibleIndivisibleThomsonThomson– Raisin bun modelRaisin bun modelRutherfordRutherford– Dense , emptyDense , emptyBohrBohr– Definite ;energyDefinite ;energy– Circular fixed distance from the nucleusCircular fixed distance from the nucleus– Greater; electronGreater; electron– Energy levels or shellsEnergy levels or shells

The Development of Atomic The Development of Atomic ModelsModels

The timeline shows the development of The timeline shows the development of atomic models from 1913 to 1932.atomic models from 1913 to 1932.

5.1

QuantaQuanta

Photons ; Photons ; bundles of energybundles of energy

The energy that is absorbed as The energy that is absorbed as electrons jump to higher energy electrons jump to higher energy levels and it is levels and it is emittedemitted when they fall when they fall to to their lower energy levelstheir lower energy levels

If electrons remain in their orbit If electrons remain in their orbit they they don’t lose energydon’t lose energy

NielsNiels Bohr and The Planetary Model of t Bohr and The Planetary Model of the Atomhe AtomAll atoms that are in the lowest energy All atoms that are in the lowest energy

level are in their normal state or level are in their normal state or groundground statestate

b. Principle Energy levelsb. Principle Energy levelsElectrons normally occupy the Electrons normally occupy the lowestlowest energy energy

levels. If an atom absorbs energy from an levels. If an atom absorbs energy from an outside source, it may cause the electrons outside source, it may cause the electrons to move to a to move to a higher energy levelshigher energy levels. This is . This is called the called the excited state This state is excited state This state is unstable.unstable.

Principle Energy levelPrinciple Energy level

The PEL denotes how far the electron The PEL denotes how far the electron is from the nucleusis from the nucleus

K- 1K- 1 ________________________

L-2L-2 ________________________

M-3M-3 ________________________

Similar to rungs on a ladderSimilar to rungs on a ladder

INC

RE

AS

ING

PE

The Bohr ModelThe Bohr ModelLike the rungs of the Like the rungs of the strange ladder, the strange ladder, the energy levels in an energy levels in an atom are not equally atom are not equally spaced. spaced.

The higher the energy The higher the energy level occupied by an level occupied by an electron, the less electron, the less energy it takes to energy it takes to move from that energy move from that energy level to the next higher level to the next higher energy level.energy level.

5.1

Spectral LinesSpectral Lines

When electrons in an atom are in the When electrons in an atom are in the excited state and return to lower excited state and return to lower energy levels the energy is emitted energy levels the energy is emitted as as

Radiant energy of a specific Radiant energy of a specific frequency which produces a frequency which produces a characteristic spectral line which can characteristic spectral line which can be used to identify elementsbe used to identify elements

Spectra of several elementsSpectra of several elements

+P+P

22

33

44

656 nm

700 nm700 nm400 nm400 nm

-e-e

Balmer series for Hydrogen

Atom

11

-e-e

-e-e

55

-e-e

486 nm

434 nm

-e-e 410 nm

n=1

n=2

n=3

n=4

Spectrum

UV

IR

Vi s ible

Ground State

Excited State

Excited StateExcited State unstable and drops back down

•Energy released as a photon

•Frequency proportional to energy drop

Excited State

But only as far as n = 2 this time

BOHR VS BOHR VS ORBITAL MODEL OF THE ATOMORBITAL MODEL OF THE ATOM

It does not represent electrons as It does not represent electrons as moving in moving in planetary orbits around planetary orbits around the nucleusthe nucleus

Electrons occupy regions of space Electrons occupy regions of space aroundaround the nucleus (not circular the nucleus (not circular paths)paths)

Electrons occupy orbitals that may Electrons occupy orbitals that may differdiffer in size, shape, or orientation in in size, shape, or orientation in spacespace

Electron ConfigurationsElectron Configurations

Ground StateGround State

The The ground stateground state is the most stable is the most stable energy state of an atom. It is the energy state of an atom. It is the nature of things to seek the lowest nature of things to seek the lowest possible energy levels. Therefore, possible energy levels. Therefore, high energy systems are high energy systems are unstableunstable

Electron ConfigurationsElectron Configurations

The way in which electrons are The way in which electrons are arranged around the nuclei of atomsarranged around the nuclei of atoms

1s1s22 2s 2s2 2 2p 2p3 3 ground stateground state

1s1s2 2 2s2s1 1 2p2p4 4 excited state excited state

Energy levelsEnergy levels

The energy levels are represented by The energy levels are represented by quantum numbersquantum numbers

N is equal to the number of the N is equal to the number of the principle energy level as referred to principle energy level as referred to under the Bohr atom and is the same under the Bohr atom and is the same as the as the period number in the periodic period number in the periodic table (horizontal)table (horizontal)

Period

Group

Alkali M

etal

Noble G

as

Halogen

Alkali E

arth Metal

2.4

SublevelsSublevels

The energy levels may be divided The energy levels may be divided into sublevels. Every PEL has one or into sublevels. Every PEL has one or more sublevels within it. The number more sublevels within it. The number of sublevels in the PEL is the same as of sublevels in the PEL is the same as the principle quantum #the principle quantum #

PEL 1 has 1 Sublevel PEL 1 has 1 Sublevel s s

PEL 2 has 2 SublevelsPEL 2 has 2 Sublevels ss pp

PEL 3 has 3 SublevelsPEL 3 has 3 Sublevels s p ds p d

PEL 4 has 4 SublevelsPEL 4 has 4 Sublevels ss pp dd ff

OrbitalsOrbitals

Each Each sublevelsublevel may consist of one or may consist of one or more more orbitals orbitals ..

Only two electrons to occupy each Only two electrons to occupy each orbitalorbital

These two electrons have opposite These two electrons have opposite spinsspins

Atomic OrbitalsAtomic OrbitalsThe numbers and kinds of atomic orbitals The numbers and kinds of atomic orbitals depend on the energy sublevel. depend on the energy sublevel.

5.1

Atomic OrbitalsAtomic OrbitalsDifferent atomic orbitals are denoted by Different atomic orbitals are denoted by letters. The letters. The ss orbitals are spherical, and orbitals are spherical, and pp orbitals are dumbbell-shaped.orbitals are dumbbell-shaped.

5.1

Atomic OrbitalsAtomic OrbitalsFour of the five Four of the five dd orbitals have the same orbitals have the same shape but different orientations in space.shape but different orientations in space.

5.1

Atomic OrbitalsAtomic Orbitals

The number of electrons allowed in each of The number of electrons allowed in each of the first four energy levels are shown here.the first four energy levels are shown here.

5.1

Electron ConfigurationsElectron Configurations– Aufbau PrincipleAufbau Principle

According to the According to the aufbau principleaufbau principle, , electrons occupy the orbitals of lowest electrons occupy the orbitals of lowest energy first. In the aufbau diagram below, energy first. In the aufbau diagram below, each box represents an atomic orbital.each box represents an atomic orbital.

5.2

3 Rules3 Rules

Pauli Exclusion PrinciplePauli Exclusion Principle– An orbital may contain only An orbital may contain only 2 electrons 2 electrons

at the most with opposite spinsat the most with opposite spins

Hunds RuleHunds Rule– Electrons occupy orbitals of equal Electrons occupy orbitals of equal

energy energy 1 electron enters each orbital 1 electron enters each orbital until all orbitals contain one electron until all orbitals contain one electron with parallel spinswith parallel spins

Electron ConfigurationsElectron ConfigurationsOrbital Filling DiagramOrbital Filling Diagram

5.2

What do electron configurations tell What do electron configurations tell us?us?

Principle energy level (PEL)Principle energy level (PEL)

Type of sublevelType of sublevel

The The numbernumber of electrons in the of electrons in the sublevelsublevel

Atomic Electron ConfigurationsAtomic Electron Configurations

1s1s22PEL

Type of sublevel and # of Orbitals

# of electrons in orbital

1s

2s

3s

4s

2p

3p

3d

Energy

Ar

1s2 2s2 2p6 3s2 3p6

4p

1s

2s

3s

4s

2p

3p

3d

Energy

Sc

1s2 2s2 2p6 3s2 3p6 3d1 4s2

4p

Valence ShellValence Shell

The outer most occupied PEL, the The outer most occupied PEL, the electrons in this shell are called electrons in this shell are called valence electronsvalence electrons an atom can’t have an atom can’t have more than 8 electrons in its more than 8 electrons in its valence valence shellshell

** ** The chemical properties of an The chemical properties of an element are determined mainly by element are determined mainly by the arrangement of electrons in the the arrangement of electrons in the valence shell**valence shell**

KernelKernel

The part of the atom including the The part of the atom including the nucleusnucleus that is stripped of its that is stripped of its valence valence electronselectrons

Ground Vs. Excited StateGround Vs. Excited State

Na 2- 8- 1Na 2- 8- 1

Na 2 – 7 -2 Na 2 – 7 -2

What element is this?What element is this?

2-8-7-3 2-8-7-3

Is it in the ground or excited state?Is it in the ground or excited state?

Ionization Energy (IE)Ionization Energy (IE)

The amount of energy needed to The amount of energy needed to remove the most loosely held remove the most loosely held electron from a neutral atomelectron from a neutral atom

Highest – Highest – noble gasesnoble gases

Metallic – Metallic – smallest IEsmallest IE

Non – Metallic – Non – Metallic – largest IElargest IE

ionic compounds consist of a cation and an anion

• the formula is always the same as the empirical formula

• the sum of the charges on the cation and anion in each formula unit must equal zero

The ionic compound NaCl

2.6

A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds

H2 H2O NH3 CH4

A diatomic molecule contains only two atoms

H2, N2, O2, Br2, HCl, CO

A polyatomic molecule contains more than two atoms

O3, H2O, NH3, CH4

2.5

2.6

A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance

An empirical formula shows the simplest whole-number ratio of the atoms in a substance

H2OH2O

molecular empirical

C6H12O6 CH2O

O3 O

N2H4 NH2

2.6

Formula of Ionic Compounds

Al2O3

2.6

2 x +3 = +6 3 x -2 = -6

Al3+ O2-

CaBr2

1 x +2 = +2 2 x -1 = -2

Ca2+ Br-

Na2CO3

1 x +2 = +2 1 x -2 = -2

Na+ CO32-

Chemical NomenclatureChemical NomenclatureIonic CompoundsIonic Compounds– often a metal + nonmetaloften a metal + nonmetal– anion (nonmetal), add “ide” to element nameanion (nonmetal), add “ide” to element name

BaCl2 barium chloride

K2O potassium oxide

Mg(OH)2 magnesium hydroxide

KNO3 potassium nitrate

2.7

Transition metal ionic compoundsTransition metal ionic compounds– indicate charge on metal with Roman numeralsindicate charge on metal with Roman numerals

FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride

FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride

Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide

2.7

Molecular compoundsMolecular compounds– nonmetals or nonmetals + metalloidsnonmetals or nonmetals + metalloids– common namescommon names

HH22O, NHO, NH33, CH, CH44, C, C6060

– element further left in periodic table is 1element further left in periodic table is 1stst

– element closest to bottom of group is 1element closest to bottom of group is 1stst

– if more than one compound can be formed if more than one compound can be formed from the same elements, use prefixes to from the same elements, use prefixes to indicate number of each kind of atomindicate number of each kind of atom

– last element ends in idelast element ends in ide

2.7

HI hydrogen iodide

NF3 nitrogen trifluoride

SO2 sulfur dioxide

N2Cl4 dinitrogen tetrachloride

NO2 nitrogen dioxide

N2O dinitrogen monoxide

Molecular Compounds

2.7

TOXIC!

Laughing Gas

An acid can be defined as a substance that yields hydrogen ions (H+) when dissolved in water.

HCl•Pure substance, hydrogen chloride•Dissolved in water (H+ Cl-), hydrochloric acid

An oxoacid is an acid that contains hydrogen, oxygen, and another element.

HNO3 nitric acid

H2CO3 carbonic acid

H2SO4 sulfuric acid2.7

2.7

A base can be defined as a substance that yields hydroxide ions (OH-) when dissolved in water.

NaOH sodium hydroxide

KOH potassium hydroxide

Ba(OH)2 barium hydroxide

2.7