Atoms, Molecules, and IonsAtoms, Molecules, and Ions

HOMEWORKHOMEWORK Read your textbook pages 74 to 78 Read your textbook pages 74 to 78

and answer q 1 to 6and answer q 1 to 6 Start a timeline in your notebook of the Start a timeline in your notebook of the

discoveries that lead to the present discoveries that lead to the present theory of the atom. Include the date theory of the atom. Include the date and name of the scientist mentioned in and name of the scientist mentioned in the book and the contribution.the book and the contribution.

HISTORYHISTORY DemocritusDemocritus 400 BC suggested that 400 BC suggested that

matter is made up of indivisible particles matter is made up of indivisible particles called atoms.called atoms.

The Law of Conservation of The Law of Conservation of MassMass

Established in 1789 by French Established in 1789 by French Chemist Antoine Lavoisier Chemist Antoine Lavoisier

States that mass is neither created States that mass is neither created nor destroyed in any chemical nor destroyed in any chemical reaction. reaction.

Or more simply, the mass of Or more simply, the mass of substances produced (products) by substances produced (products) by a chemical reaction is always equal a chemical reaction is always equal to the mass of the reacting to the mass of the reacting substances (reactants). substances (reactants).

LAW OF DEFINITE LAW OF DEFINITE PROPORTIONSPROPORTIONS

Every compound is a combination of a Every compound is a combination of a fixed proportion by mass between the fixed proportion by mass between the elements that compose the sample.elements that compose the sample.

Water is always 1 g of H and 8 g of OWater is always 1 g of H and 8 g of O CO2 is always 12 g of C and 32 of O CO2 is always 12 g of C and 32 of O

LAW OF MULTIPLE LAW OF MULTIPLE PROPORTIONSPROPORTIONS

When the same elements combine to When the same elements combine to form different compounds, they do so in form different compounds, they do so in mass ratios that can be expressed by mass ratios that can be expressed by small whole numbers.small whole numbers.

CO carbon monoxide 12 g C 16 g OCO carbon monoxide 12 g C 16 g O CO2 carbon dioxide 12 g C 32 g OCO2 carbon dioxide 12 g C 32 g O

First Atomic Theory First Atomic Theory Dalton (1766-1844) Dalton (1766-1844)

All elements are composed of indivisible atoms.All elements are composed of indivisible atoms. Atom of the same elements are identical.Atom of the same elements are identical. Atoms of different elements differ in their physical Atoms of different elements differ in their physical

and chemical properties. and chemical properties. Atoms of different elements combine to form Atoms of different elements combine to form

compounds in simple whole number ratios.compounds in simple whole number ratios. Chemical reactions occur when atoms are Chemical reactions occur when atoms are

separated, joined or rearranged, but they can not separated, joined or rearranged, but they can not change.change.

Experiments to determine Experiments to determine what an atom waswhat an atom was

J. J. Thomson (1897)- used Cathode J. J. Thomson (1897)- used Cathode ray tubesray tubes

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive end.positive end.

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field, he found that By adding an electric field, he found that the moving pieces were negative the moving pieces were negative

+

-

OBJECTIVE : WHAT IS INSIDE THE OBJECTIVE : WHAT IS INSIDE THE

ATOM?ATOM? Experiments that lead to find what is Experiments that lead to find what is

inside the atominside the atom Rutherford gold foil experiment – Rutherford gold foil experiment – MillikanMillikan

Thomsom’s conclusionsThomsom’s conclusions Thomson named the cathodic rays Thomson named the cathodic rays

electrons and concluded that they must electrons and concluded that they must be a part of atoms of all elements. be a part of atoms of all elements.

The Atom, circa 1900:The Atom, circa 1900:

““Plum pudding” model, Plum pudding” model, put forward by put forward by Thompson.Thompson.

Positive sphere of matter Positive sphere of matter with negative electrons with negative electrons imbedded in it.imbedded in it.

The Gold foil experimentThe Gold foil experiment In 1911 Ernest Rutherford designed an In 1911 Ernest Rutherford designed an

experiment using alpha particles and experiment using alpha particles and thin gold foil - “gold foil experiment”. thin gold foil - “gold foil experiment”. Rutherford was very surprised by his Rutherford was very surprised by his finding and his conclusions led to which finding and his conclusions led to which became known as the “planetary” model became known as the “planetary” model of the atom. of the atom.

Rutherford’s ExperimentRutherford’s Experiment Used uranium to produce alpha Used uranium to produce alpha

particles.particles. Aimed alpha particles at gold foil by Aimed alpha particles at gold foil by

drilling hole in lead block.drilling hole in lead block. Since the mass is evenly distributed in Since the mass is evenly distributed in

gold atoms alpha particles should go gold atoms alpha particles should go straight through.straight through.

Used gold foil because it could be made Used gold foil because it could be made atoms thin.atoms thin.

Lead block

Uranium

Gold Foil

Florescent Screen

What he got

Review of Rutherford ExperimentReview of Rutherford Experiment Subatomic particlesSubatomic particles

Discovery of the NucleusErnest Rutherford Ernest Rutherford shot shot particles at a particles at a thin sheet of gold foil thin sheet of gold foil and observed the and observed the pattern of scatter of pattern of scatter of the particles.the particles.

How he explained it

+

Atom is mostly emptyAtom is mostly empty Small dense,Small dense,

positive piecepositive pieceat center.at center.

Alpha particlesAlpha particlesare deflected byare deflected by

it if they get close it if they get close enough. enough.

+

The Nuclear AtomThe Nuclear Atom

Since some particles Since some particles were deflected at were deflected at large angles, large angles, Thompson’s model Thompson’s model could not be correct.could not be correct.

Observations Observations Most of the alpha particles pass straight Most of the alpha particles pass straight

through the gold foil. through the gold foil. Some of the alpha particles get Some of the alpha particles get

deflected by very small amounts. deflected by very small amounts. A very few get deflected greatly. A very few get deflected greatly. Even fewer get bounced of the foil and Even fewer get bounced of the foil and

back to the left. back to the left.

ConclusionsConclusions The atom is 99.99% empty space. The atom is 99.99% empty space. The nucleus contains a positive charge The nucleus contains a positive charge

and most of the mass of the atom.   and most of the mass of the atom.   The nucleus is approximately 100,000 The nucleus is approximately 100,000

times smaller than the atom. times smaller than the atom.

VocabularyVocabulary Deflected: curved or bent downward. Deflected: curved or bent downward. To Scatter: to separate and drive off in To Scatter: to separate and drive off in

various directions; to disperse various directions; to disperse To Bounce: To rebound,  move up and To Bounce: To rebound,  move up and

down repeatedly.down repeatedly.

Other Subatomic ParticlesOther Subatomic Particles Protons were discovered by Rutherford Protons were discovered by Rutherford

in 1919.in 1919. Neutrons were discovered by James Neutrons were discovered by James

Chadwick in 1932.Chadwick in 1932.

The Bohr ModelThe Bohr Model Niels Bohr proposed a model of the Niels Bohr proposed a model of the

atom based on the solar system.atom based on the solar system. It was wrong but some of his ideas we It was wrong but some of his ideas we

still used. It was one step in the still used. It was one step in the direction of the last model for the atom.direction of the last model for the atom.

First let’s take a look at what is inside First let’s take a look at what is inside the atom.the atom.

Subatomic ParticlesSubatomic Particles

Protons and electrons are the only particles that Protons and electrons are the only particles that have a charge.have a charge.

Protons and neutrons have essentially the same Protons and neutrons have essentially the same mass. They are located inside the nucleus.mass. They are located inside the nucleus.

The mass of an electron is so small we ignore it.The mass of an electron is so small we ignore it.

Atomic Number (Z)Atomic Number (Z) The number of protons in the The number of protons in the

nucleus. It identifies the nucleus. It identifies the element. In the neutral atomelement. In the neutral atom

# protons = # electrons# protons = # electrons

Atomic NumberAtomic Number

All atoms of the same element have the same All atoms of the same element have the same number of protons: number of protons:

The atomic number (Z)The atomic number (Z)

Mass Number (A)Mass Number (A)* It is not in the periodic table * It is not in the periodic table

but is the atomic mass but is the atomic mass rounded offrounded off

Protons plus neutrons in the atom Protons plus neutrons in the atom A= A= # protons + # neutrons# protons + # neutrons *In the table we can find the Atomic Mass. *In the table we can find the Atomic Mass. Number of Neutrons =Mass number-Atomic number=Mass number-Atomic number

ISOTOPIC SYMBOLISOTOPIC SYMBOL• Atomic number (Z) = number of protons in the Atomic number (Z) = number of protons in the

nucleus.nucleus.• Mass number (A) = total number of nucleons Mass number (A) = total number of nucleons

in the nucleus (i.e., protons and neutrons).in the nucleus (i.e., protons and neutrons).

• By convention, for element X, we write By convention, for element X, we write

ZZAAXX

Isotopes, Atomic Numbers, and Mass Numbers

• Atomic number (Z) = number of protons in the

nucleus.• Mass number (A)

= total number of nucleons in the nucleus (i.e., protons and neutrons).

• By convention, for element X, we write ZAX.

• Isotopes have the same Z but different A.• We find Z on the periodic table.

Mass NumberMass Number

The mass of an atom in atomic mass units The mass of an atom in atomic mass units (amu) is the total number of protons and (amu) is the total number of protons and neutrons in the atom.neutrons in the atom.

Mass Number (A)Mass Number (A)* It is not in the periodic table* It is not in the periodic table

Protons plus neutrons in the atom Protons plus neutrons in the atom A= A= # protons + # neutrons# protons + # neutrons *In the table we can find the Atomic Mass. *In the table we can find the Atomic Mass. Number of Neutrons =Mass number-Atomic number=Mass number-Atomic number

IsotopesIsotopes atoms with same number of protons and atoms with same number of protons and

different number of neutrons. Same different number of neutrons. Same atomic number different mass number.atomic number different mass number.

SAME ELEMENT with different # of SAME ELEMENT with different # of neutrons!neutrons!

Isotopes:Isotopes:

Atoms of the same element with different masses.Atoms of the same element with different masses. Isotopes have different numbers of neutrons.Isotopes have different numbers of neutrons.

116C 12

6C 136C 14

6C

Atomic Mass UnitAtomic Mass Unit

(amu) is one-twelfth the mass of a carbon-12 atom.

Atomic MassAtomic Mass is the weighted average of the mass of is the weighted average of the mass of

all the isotopes of one element.all the isotopes of one element. It takes into consideration the mass of It takes into consideration the mass of

the different isotopes of the element and the different isotopes of the element and their natural abundancetheir natural abundance

Hw questionsHw questions1)1) 33

2)2) 22

3)3) 44

4)4) 44

5)5) 44

6)6) 22

7)7) 22

8)8) 44

9)9) 33

10)10) 44

11)11) 22

11) 211) 2 12) 412) 4

Temperature reviewTemperature review17)17) 22

18)18) 44

19)19) 11

20)20) 22

21)21) 44

22)22) 33

23)23) 44

24)24) 11

25)25) 11

26)26) 33

27)27) 11

28)28) 33

29)29) 33

DECEMBER 13DECEMBER 13 The Bohr AtomThe Bohr Atom Energy levels – shellsEnergy levels – shells Electron configurationElectron configuration

Planetary ModelPlanetary Model Neils BohrNeils Bohr 1913 1913 Electrons are arranged in orbits around Electrons are arranged in orbits around

the nucleus.the nucleus. He proposed that electrons in a He proposed that electrons in a

particular orbit have a fixed energy. The particular orbit have a fixed energy. The electrons cannot fall into the nucleus.electrons cannot fall into the nucleus.

Bohr’s Atom

electrons in orbits

nucleus

Energy levelEnergy level is the region around the nucleus where is the region around the nucleus where

the electron is moving. the electron is moving. As the electrons are further away from As the electrons are further away from

the nucleus they have more energy. the nucleus they have more energy. The closest orbits or energy levels to The closest orbits or energy levels to the nucleus have low energy.the nucleus have low energy.

He named the orbits with letters He named the orbits with letters beginning with k,l,m,n…beginning with k,l,m,n…

The first energy level could hold 2 The first energy level could hold 2 electrons. electrons.

Second energy level could hold up to 8 Second energy level could hold up to 8 electronselectrons

Electron ConfigurationsElectron Configurations Indicates how the electrons are located Indicates how the electrons are located

in the atom.in the atom. Niels Bohr proposed that electrons are Niels Bohr proposed that electrons are

located in energy levels at different located in energy levels at different distances from the nucleus.distances from the nucleus.

2-8-3 total of electrons=132-8-3 total of electrons=13 3 energy levels3 energy levels

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

What do these particles consist of?

ATOMIC STRUCTUREATOMIC STRUCTURE

Particle

proton

neutron

electron

Charge

+ ve charge

-ve charge

No charge

1

1

nil

Mass

ATOMIC STRUCTUREATOMIC STRUCTURE

MASS NUMBER

the number of protons and neutrons in an atom

the number of protons in an atom

HeHe22

44

number of electrons = number of protons

Atomic number

ATOMIC STRUCTUREATOMIC STRUCTURE

Electrons are arranged in Energy Levels

or Shells around the nucleus of an atom.

• first shell a maximum of 2 electrons

• second shell a maximum of 8

electrons

• third shell a maximum of 8

electrons

SUMMARYSUMMARY

1. The Atomic Number of an atom = number of

protons in the nucleus.

2. The Atomic Mass of an atom = number of

Protons + Neutrons in the nucleus.

3. The number of Protons = Number of Electrons.

4. Electrons orbit the nucleus in shells.

5. Each shell can only carry a set number of electrons.

DECEMBER 17 A closer look at the Bohr model How did Bohr came to the conclusion

that the electron moved in orbits?

TEXTBOOK PAGES 90 TO 94

Bohr ModelBohr Model 1 An electron in a permitted orbit has a 1 An electron in a permitted orbit has a

specific energy an is in an “allowed” specific energy an is in an “allowed” energy state. It will not spiral into the energy state. It will not spiral into the nucleusnucleus

2 Energy is emitted or absorbed by the 2 Energy is emitted or absorbed by the electron only as the electron changes electron only as the electron changes from one allowed state to otherfrom one allowed state to other

Energy levelsor shells

Electrons with the lowest energy are found in the energy level closest to the nucleus

Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

The Nature of EnergyThe Nature of Energy

A mystery involved the A mystery involved the emission spectra emission spectra observed from energy observed from energy emitted by atoms and emitted by atoms and molecules.molecules.

When gases at low pressure When gases at low pressure were placed in a tube and were placed in a tube and were subjected to high were subjected to high voltage, light of different voltage, light of different colors appearedcolors appeared

Continuous Spectra• Radiation composed of only one wavelength is called

monochromatic.• Radiation that spans a whole array of different

wavelengths is called continuous.• White light can be separated into a continuous spectrum

of colors.• Note that there are no dark spots on the continuous

spectrum that would correspond to different lines.

Line Spectra and the Bohr Line Spectra and the Bohr ModelModel

Line SpectraLine SpectraIf high voltage is applied to atoms in gas If high voltage is applied to atoms in gas

phase at low pressure light is emitted phase at low pressure light is emitted from the gas.from the gas.

If the light is analyzed the spectrum If the light is analyzed the spectrum obtained is not continuous.obtained is not continuous.

SPECTROSCOPESPECTROSCOPE

Line Spectra.

When the light from a discharge tube is analyzed only some bright lines appeared.

Waves Waves carry energy and have

cycles. Each cycle of a wave begins at the origin and ends in the origin.

The wavelength (lambda) of a wave is a measurement of how long it is. It is measured in length units.

The longer the wavelength, the smaller amount of energy that is associated with.

* Short wavelength, high energy.

* Long wavelength, low energy.

Waves Light consists of electromagnetic waves

How is Light Energy related to Color?

White light is made up of all colors of the spectrum (ROYGBIB)When passed through a prism a continuous spectrum (rainbow effect) is obtained

Nature of light Light is a form of electromagnetic wave.

Each color of the visible light is associated with a different wavelength.

R (700 nm) O Y G B I V (400nm)

Line SpectraLine SpectraIf high voltage is applied to atoms in gas If high voltage is applied to atoms in gas

phase at low pressure light is emitted phase at low pressure light is emitted from the gas.from the gas.

If the light is analyzed with an If the light is analyzed with an SPECTROSCOPE the spectrum SPECTROSCOPE the spectrum obtained is not continuous.obtained is not continuous.

Line Spectra

This type of spectra is used to identify atoms of different elements and were used to explain the new model of the atom.

Bright line spectrum When an atom ABSORBS energy, the

electrons JUMP (LEAP) to a higher energy level. They are in the EXCITED STATE.

When the electrons return to the normal level (GROUND STATE) , they emit energy as LIGHT. The light emitted light produce the bright line spectrum that is characteristic of each element.

Electrons Surround the Nucleus

Electrons surround the nucleus and travel at the speed of light

They are found in only certain allowed energy levels or orbitals

Electrons are at the lowest energy level – the ground state.

Different Energy States are Possible When the electrons in an atom

become excited by absorbing energy from the surroundings, they jump to new higher energy levels.

The excited state is less stable than the lower energy state therefore the electron falls back or returns to the lower energy ground state.

Return to Ground State

When electrons fall back a wave with a specific amount of energy is emitted – called a photon. If we see color then the emission is in the visible range

We perceive this as unique colors associated with particular elements

Ground state configuration vs excited state configuration

11Na 2-8-1 This is the ground state.

If atom is excited some possible electron configuration would be

2-7-2 or 1-8-2 or 1-6-3 The number of electrons must add to the

atomic number but the order is not the one that appears in the periodic table.

The wave-mechanical model of the atom

The Wave Model Today’s atomic model

is based on the principles of wave mechanics.

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

Quantum Model

The modern model of the atom is called the quantum model or the wave-mechanical model.

By 1900 scientist were studying energy and waves.

It was proposed that energy was made of tiny packets called quanta, these packets acted like particles.

That implied that light could behave as a wave and also as a particle.

Quantum – singular – package or bundle or energy. If the energy is light is a photon.

Quanta is the plural of quantum.

Duality wave -particle Louis De Broglie

discovered that the electron also behaves sometimes as a particle and sometimes as a wave

Orbitals In the wave-mechanical model the electrons

are found not in fixed orbits around the nucleus but in ORBITALS.

ORBITALS are regions in which an electron of a particular amount of energy is most likely to be found.

Probability The wave mechanical model describes

the atom using PROBABILITY of finding electrons at different distances from the nucleus.

Quantum theory In 1926 Erwin

Schrodinger used the quantum theory to write an equation describing the location and energy of the electron in the atom of hydrogen.

The quantum model principles Electrons are found in orbitals. There are different energy levels. Electrons can gain or

lose fixed amounts of energy (quanta) to move to different energy levels.

When the electrons occupy the lowest available orbitals the atom is in the ground state.

If the atom absorbs a quantum of energy the electrons jump to a higher energy level. This UNSTABLE CONDITION is called EXCITED STATE.

When the electrons return to the ground state they emit the same amount of energy they absorbed as LIGHT of different colors.

The emitted light can be analyzed with a spectroscope and the resulting spectrum can be used to identify the atoms.

Energy levels A space in which

electrons are likely to be found.

Electrons whirl about the nucleus billions of times in one second

They are not moving around in random patterns.

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

Energy levelsor shells

Electrons with the lowest energy are found in the energy level closest to the nucleus

Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

Modern Atomic TheoryModern Atomic Theory The atom is The atom is

mostly empty mostly empty space.space.

Two regionsTwo regions Nucleus- protons Nucleus- protons

and neutrons.and neutrons. Electron cloud- Electron cloud-

region where you region where you might find an might find an electron.electron.

SET 1 & 2 ATOMIC SET SET 1 & 2 ATOMIC SET ANSWERSANSWERS

1 -1 1 -1 2 - 22 - 2 3 - 43 - 4 4 – 24 – 2 5 – 35 – 3 6 – 46 – 4 7 – 47 – 4 8 - 48 - 4

9 – 3 17/31-49 – 3 17/31-4

10 – 3 18/32 110 – 3 18/32 1 11 – 1 19/33 311 – 1 19/33 3 12 – 3 20 -212 – 3 20 -2 13/38 4 21- 113/38 4 21- 1 14/28 1 22-114/28 1 22-1 15/29-315/29-3 16/30-1 16/30-1

What happens when the number of protons and the number of electrons in an atom are not equal?

IONS

Nuclear Charge

Is the number of protons!

Atoms are neutral and contain same Atoms are neutral and contain same number of electrons than protons. In a number of electrons than protons. In a chemical reactions atoms can lose, chemical reactions atoms can lose, gain or share electrons.gain or share electrons.

When an atom loses an electron it When an atom loses an electron it becomes a positive ion. When it gains becomes a positive ion. When it gains an electron it becomes a negative ion.an electron it becomes a negative ion.

The nucleus always remains the same The nucleus always remains the same in a chemical reaction.in a chemical reaction.

The number of protons and neutrons The number of protons and neutrons never change.never change.

Ion A charged particle When an atom loses or gains electrons

it becomes an ION. Remember protons can not be touched! If an atom loses electron the ion will be

positive (more protons than electrons) If an atom gains electrons it will became

negative (more electrons than protons)

Metals lose electrons and become Metals lose electrons and become positive ions (caTions)positive ions (caTions)

Non metals gain electrons and become Non metals gain electrons and become negative ions ( aNions)negative ions ( aNions)

Indivisible Electron Nucleus Orbit Electron Cloud

Greek X

Dalton X

Thomson X

Rutherford X X

Bohr X X X

Wave X X X