chapter 4 atomic structure section 4.1 studying atoms section 4.2 the structure of an atom section...
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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)