Chapter 4 Atomic Chapter 4 Atomic StructureStructure

Section 4.1 Studying AtomsSection 4.1 Studying AtomsSection 4.2 The Structure of an AtomSection 4.2 The Structure of an AtomSection 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

**Studying atoms is difficult b/c they are **Studying atoms is difficult b/c they are so small in size.so small in size.

Ancient Greek Models of AtomsAncient Greek Models of Atoms Democritus (philosopher)- believed that all Democritus (philosopher)- believed that all

matter consisted of extremely small matter consisted of extremely small particles that could not be dividedparticles that could not be divided

atomosatomos(Greek)-”uncut” or “indivisible”(Greek)-”uncut” or “indivisible” Different types of atoms with specific sets Different types of atoms with specific sets

of properties.of properties.

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Ancient Greek Models of AtomsAncient Greek Models of Atoms Aristotle: there was no limit to the # Aristotle: there was no limit to the #

of times matter could be dividedof times matter could be divided All substances were built up from All substances were built up from

only four elements—earth, air, fire, only four elements—earth, air, fire, and water.and water.

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Dalton’s Atomic TheoryDalton’s Atomic Theory John DaltonJohn Dalton -England (1766); -England (1766);

teacher: interested in predicting teacher: interested in predicting weatherweather

Studied behavior of gases in the air Studied behavior of gases in the air (way gas exerts pressure); (way gas exerts pressure); a gas a gas consists of individual particlesconsists of individual particles

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Evidence for Atoms (Dalton)Evidence for Atoms (Dalton) Measured masses of elements that Measured masses of elements that

combine when compounds formcombine when compounds form The ratio of the masses of the The ratio of the masses of the

elements in the compound is always elements in the compound is always the samethe same (compounds have a fixed (compounds have a fixed composition)composition)

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Dalton’s TheoryDalton’s Theory Developed theory to explain why Developed theory to explain why

elements in a compound always join elements in a compound always join in the same wayin the same way

Key Concept: Dalton proposed the Key Concept: Dalton proposed the theory that theory that all matter is made up of all matter is made up of individual particles called atoms, individual particles called atoms, which cannot be divided.which cannot be divided.

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Dalton’s TheoryDalton’s Theory All elements are composed of atoms.All elements are composed of atoms. All atoms of the same elements have the All atoms of the same elements have the

same mass; atoms of different elements same mass; atoms of different elements have different masses.have different masses.

Compounds contain atoms of more than Compounds contain atoms of more than one element.one element.

In a particular compound, atoms of In a particular compound, atoms of different elements always combine the different elements always combine the same way.same way.

Section 4.1 Studying AtomsSection 4.1 Studying Atoms Thompson’s Model of the AtomThompson’s Model of the Atom

When some materials are rubbed, they When some materials are rubbed, they gain the ability to attract or repel other gain the ability to attract or repel other materials.materials.

Based on their behavior: either have Based on their behavior: either have positive or a negative charge (like charges positive or a negative charge (like charges repel; opposites attract)repel; opposites attract)

Charged particles (some) can flow from Charged particles (some) can flow from one location to another. (electric current)one location to another. (electric current)

J.J. Thompson- used electric current to J.J. Thompson- used electric current to learn more about atomslearn more about atoms

Thomson’s ExperimentsThomson’s Experiments

Figure 5

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Evidence for Subatomic ParticlesEvidence for Subatomic Particles Thompson concluded that Thompson concluded that particles in particles in

the beam had a negative charge b/c the beam had a negative charge b/c they were attracted to the positive they were attracted to the positive plate.plate.

Key Concept: Thompson’s Key Concept: Thompson’s experiments provided the first experiments provided the first evidence that evidence that atoms are made of atoms are made of even smaller particles.even smaller particles.

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Thompson’s ModelThompson’s Model An atom is neutral (no neg. or pos. An atom is neutral (no neg. or pos.

charge); charge); how is that possiblehow is that possible?? If atoms have negative charge, If atoms have negative charge, there there

must be a positive charge!must be a positive charge! Thompson’s model-negative charges Thompson’s model-negative charges

evenly scattered throughout w/ a evenly scattered throughout w/ a positively charged mass of matter positively charged mass of matter (plum pudding model)(plum pudding model)

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Rutherford’s Atomic TheoryRutherford’s Atomic Theory Rutherford’s Hypothesis (Ernest Rutherford’s Hypothesis (Ernest

Rutherford)-Rutherford)-discovered that uranium discovered that uranium emits fast-moving particles that have emits fast-moving particles that have a positive charge (alpha particles)a positive charge (alpha particles)

What happens to alpha particles What happens to alpha particles when they pass through a thin sheet when they pass through a thin sheet of gold?of gold?

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

Rutherford’s HypothesisRutherford’s Hypothesis Hypothesized that mass and charge Hypothesized that mass and charge

at any location in the gold would be at any location in the gold would be too small to change the path of an too small to change the path of an alpha particle.alpha particle.

I.e. Most particles would travel in a I.e. Most particles would travel in a straight line/path; others would be straight line/path; others would be deflected slightlydeflected slightly

Section 4.1 Studying AtomsSection 4.1 Studying Atoms

The Gold Foil ExperimentThe Gold Foil Experiment Narrow beam of alpha particles aimed at Narrow beam of alpha particles aimed at

goldgold Screen around the gold produced flashes Screen around the gold produced flashes

of light when struck by alpha particles of light when struck by alpha particles ((path of alpha particles after passing path of alpha particles after passing through gold was determinedthrough gold was determined))

More particles were deflected than More particles were deflected than expected.expected.

The Gold Foil The Gold Foil ExperimentExperiment

Figure 5

Section 4.1 Studying AtomsSection 4.1 Studying Atoms Discovery of the NucleusDiscovery of the Nucleus

Alpha particles came close to another charged Alpha particles came close to another charged object; greater deflectionobject; greater deflection

Many alpha particles passed through the goldMany alpha particles passed through the gold **Atoms are made up mostly of empty space.**Atoms are made up mostly of empty space. ((Concluded that positive charge of an atom is not Concluded that positive charge of an atom is not

evenly spread throughout the atomevenly spread throughout the atom)) The positive charge is concentrated in a very The positive charge is concentrated in a very

small, central area (small, central area (nucleus-a dense positively nucleus-a dense positively charged mass in the atom’s centercharged mass in the atom’s center))

Key Concept: According to Rutherford’s model, Key Concept: According to Rutherford’s model, all of an atom’s positive charge is concentrated in all of an atom’s positive charge is concentrated in its nucleus.its nucleus.

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Properties of Subatomic ParticlesProperties of Subatomic Particles Rutherford-evidence for the Rutherford-evidence for the

existence of 2 subatomic particles; existence of 2 subatomic particles; predicted a thirdpredicted a third

Key Concept: Key Concept: Protons, electrons, and Protons, electrons, and neutrons are subatomic particles.neutrons are subatomic particles.

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Properties of Subatomic Particles: Properties of Subatomic Particles: ProtonsProtons

ProtonProton-a positively charged -a positively charged subatomic particlesubatomic particle

Found in the nucleus of an atomFound in the nucleus of an atom Each proton has a Each proton has a 1+ charge1+ charge

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Properties of Subatomic Particles: Properties of Subatomic Particles: ElectronsElectrons

ElectronElectron-a negatively charged -a negatively charged subatomic particlesubatomic particle

Found in the space outside the Found in the space outside the nucleusnucleus

Each electron has a Each electron has a 1- charge1- charge

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Properties of Subatomic Particles: Properties of Subatomic Particles: NeutronsNeutrons

NeutronNeutron-a neutral subatomic particle -a neutral subatomic particle Found in the nucleus of an atomFound in the nucleus of an atom Has a Has a mass almost exactly equal to mass almost exactly equal to

that of a protonthat of a proton

Figure 12

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Comparing Subatomic ParticlesComparing Subatomic Particles Key Concept: Protons, electrons, and Key Concept: Protons, electrons, and

neutrons can be neutrons can be distinguished by mass, distinguished by mass, charge, and location in an atom.charge, and location in an atom.

Protons and neutrons have the same massProtons and neutrons have the same mass An electron’s charge is equal in size to, but An electron’s charge is equal in size to, but

is opposite of a proton’s chargeis opposite of a proton’s charge

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Comparing Subatomic ParticlesComparing Subatomic Particles Neutrons have no charge (neutral)Neutrons have no charge (neutral) Protons and neutrons are inside the Protons and neutrons are inside the

nucleus of an atom.nucleus of an atom. Electrons are outside of the nucleus.Electrons are outside of the nucleus.

electron

neutron

proton

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Atomic Number and Mass NumberAtomic Number and Mass Number Dalton: atoms of one element are Dalton: atoms of one element are

different from the atoms of another different from the atoms of another element.element.

Discovery of subatomic Discovery of subatomic particles=ability to describe the particles=ability to describe the differences between atoms of differences between atoms of elementselements

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Atomic NumberAtomic Number # of protons in an atom of an element# of protons in an atom of an element # of protons in the atom of an element is # of protons in the atom of an element is alwaysalways

the samethe same # of protons in the atoms of different elements is # of protons in the atoms of different elements is

differentdifferent Atoms are neutral: each positive charge is Atoms are neutral: each positive charge is

balanced by a negative charge balanced by a negative charge (ie. The atomic (ie. The atomic number of an element is equal to the # of number of an element is equal to the # of electrons in an atom.)electrons in an atom.)

Ie. 2 protons=2+, so atom has 2 electrons=2-: Ie. 2 protons=2+, so atom has 2 electrons=2-: so so 2 + -2=0 NO CHARGE!2 + -2=0 NO CHARGE!

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

Mass NumberMass Number Def.-Def.-the sum of the protons and the sum of the protons and

neutrons in the nucleus of an atomneutrons in the nucleus of an atom Ex. Al (Aluminum): 13 protons and 14 Ex. Al (Aluminum): 13 protons and 14

neutrons; neutrons; mass number is 27mass number is 27 Find the # of neutrons: need mass # Find the # of neutrons: need mass #

and atomic #and atomic # #neutrons=mass# - atomic ##neutrons=mass# - atomic #

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

IsotopesIsotopes Def.-atoms of the same element that Def.-atoms of the same element that

have have different numbers of neutronsdifferent numbers of neutrons and and different mass numbersdifferent mass numbers

Key Concept: Key Concept: Isotopes of an element Isotopes of an element have the same atomic number but have the same atomic number but different mass numbers because different mass numbers because they have different numbers of they have different numbers of neutrons.neutrons.

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

IsotopesIsotopes Ex. Oxygen (O)-has 3 isotopes: O-Ex. Oxygen (O)-has 3 isotopes: O-

16, O-17, O-1816, O-17, O-18 All have 8 protons; all react w/ All have 8 protons; all react w/

hydrogen (water) or w/ iron (rust)hydrogen (water) or w/ iron (rust)

Section 4.2 The Structure of an Section 4.2 The Structure of an AtomAtom

IsotopesIsotopes Hard to notice any difference in Hard to notice any difference in

physical or chemical properties of physical or chemical properties of most elements and their isotopes most elements and their isotopes except….except….HydrogenHydrogen

H-1 (no neutrons); H-2 (1 neutron); H-1 (no neutrons); H-2 (1 neutron); H-3 (2 neutrons)H-3 (2 neutrons)

Add neutron=doubles hydrogen’s Add neutron=doubles hydrogen’s mass so…mass so…water w/ H-2=heavy waterwater w/ H-2=heavy water

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Bohr’s Model of the AtomBohr’s Model of the Atom Niels Bohr (1885-1962) Danish physicist; Niels Bohr (1885-1962) Danish physicist;

had worked w/ Rutherfordhad worked w/ Rutherford Model focused on electrons; Model focused on electrons; move like move like

planets orbiting the sunplanets orbiting the sun

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Energy LevelsEnergy Levels Def.-Def.-the possible energies that electrons in the possible energies that electrons in

an atom can havean atom can have Bohr’s model: Bohr’s model: electrons move w/ constant electrons move w/ constant

speed in fixed orbits around the nucleusspeed in fixed orbits around the nucleus Each electron has a specific amt. of energyEach electron has a specific amt. of energy If atom gains or loses energy, the If atom gains or loses energy, the

electron’s energy can changeelectron’s energy can change

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Energy LevelsEnergy Levels An electron cannot exist between An electron cannot exist between

energy levelsenergy levels Key Concept: An electron in an atom Key Concept: An electron in an atom

can move from one energy level to can move from one energy level to another when the atom gains or another when the atom gains or loses energy.loses energy.

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Evidence of Energy LevelsEvidence of Energy Levels Scientists can measure the energy Scientists can measure the energy

gained when electrons absorb energy gained when electrons absorb energy (move to higher energy level)(move to higher energy level)

Can also measure the energy Can also measure the energy released when the electron returns released when the electron returns to a lower energy levelto a lower energy level

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Electron Cloud ModelElectron Cloud Model Bohr: electrons moved like planets in Bohr: electrons moved like planets in

the solar system (WRONG)the solar system (WRONG) Today: scientists know that electrons Today: scientists know that electrons

move in a less predictable waymove in a less predictable way Electron cloudElectron cloud-a visual model of the -a visual model of the

most likely locations for electrons in most likely locations for electrons in an atoman atom

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Electron Cloud ModelElectron Cloud Model Cloud is denser-higher probability of Cloud is denser-higher probability of

finding an electron at that locationfinding an electron at that location Key Concept: Key Concept: Scientists use the Scientists use the

electron cloud model to describe the electron cloud model to describe the possible locations of electrons possible locations of electrons around the nucleus.around the nucleus.

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Atomic OrbitalsAtomic Orbitals Electron cloud=all orbitals in an atomElectron cloud=all orbitals in an atom Orbital-a region of space around the Orbital-a region of space around the

nucleus where an electron is likely to nucleus where an electron is likely to be foundbe found

Key Concept: An electron cloud is a Key Concept: An electron cloud is a good good approximationapproximation of how electrons of how electrons behave in their orbitals.behave in their orbitals.

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Atomic OrbitalsAtomic Orbitals Lowest energy level (Lowest energy level (where electron where electron

has least energyhas least energy) has ) has only 1 orbitalonly 1 orbital Each orbital can contains a maximum Each orbital can contains a maximum

of of 2 electrons.2 electrons.

Number of Orbitals and Electrons in Number of Orbitals and Electrons in Energy LevelsEnergy Levels

Figure 15

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Electron ConfigurationsElectron Configurations Def.-Def.-the arrangement of electrons in the arrangement of electrons in

the orbitals of an atomthe orbitals of an atom Key Concept: The most stable Key Concept: The most stable

electron configuration is one in which electron configuration is one in which the the electrons are in orbitals with the electrons are in orbitals with the lowest possible energieslowest possible energies

Section 4.3 Modern Atomic TheorySection 4.3 Modern Atomic Theory

Electron ConfigurationsElectron Configurations When electrons in an atom have the When electrons in an atom have the

lowest possible energies—atom is in lowest possible energies—atom is in its its ground state.ground state.

An electron can move to orbital w/ a An electron can move to orbital w/ a higher energy (higher energy (excited state—less excited state—less stable)stable)