of atoms and elements historical and modern perspectives

Of Atoms and Of Atoms and ElementsElements

Historical and Modern Historical and Modern PerspectivesPerspectives

1831: Michael Faraday1831: Michael Faraday

Discovery of Discovery of ionsions AnionAnion : negatively-charged particles : negatively-charged particles CationCation : positively-charged particles : positively-charged particles

Science of electrolysis: splitting Science of electrolysis: splitting substances using electricitysubstances using electricity

Determined that atoms were Determined that atoms were electrical in natureelectrical in nature

1895: Wilhelm Roentgen1895: Wilhelm Roentgen

Studying glow produced from Studying glow produced from cathode rayscathode rays

Noticed that the glow could be Noticed that the glow could be transmitted to chemically-treated transmitted to chemically-treated paperpaper

X-rays discovered, but not fully X-rays discovered, but not fully understoodunderstood

1895: Antoine Bequerel1895: Antoine Bequerel

Photographic film fogged when Photographic film fogged when placed close to samples of uraniumplaced close to samples of uranium

Required no input of energyRequired no input of energy Graduate student Marie Curie and Graduate student Marie Curie and

later her husband Pierre continued later her husband Pierre continued to study the phenomenonto study the phenomenon

Marie coined the term Marie coined the term “radioactivity”“radioactivity”

1897: Joseph John 1897: Joseph John ThomsonThomson

Showed that the beam created in a Showed that the beam created in a cathode-ray tube was attracted to a cathode-ray tube was attracted to a positive plate and repelled by a positive plate and repelled by a negative platenegative plate

The particles were the same The particles were the same regardless of the material from regardless of the material from which the ray was generatedwhich the ray was generated

Coined the term “electrons” for the Coined the term “electrons” for the negative particlesnegative particles

Thomson’s ExperimentThomson’s Experiment

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Thomson’s ModelThomson’s Model

Realized that the negatively-charged Realized that the negatively-charged particles had to be balanced by a particles had to be balanced by a positively-charged substancepositively-charged substance

““Plum Pudding Model”Plum Pudding Model”

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1909: Robert Millikan1909: Robert Millikan

Received Nobel Prize in 1923 for Received Nobel Prize in 1923 for workwork

Calculated mass and charge of Calculated mass and charge of electronselectrons Mass = Mass = 0.000 000 000 000 000 000 000 000 0.000 000 000 000 000 000 000 000

000 000 911 kg000 000 911 kg

Millikan’s ExperimentMillikan’s Experiment

1.1. Sprayed oil droplets into a chamberSprayed oil droplets into a chamber2.2. Calculated mass of droplets by how fast Calculated mass of droplets by how fast

they fall (gravity)they fall (gravity)3.3. Charge 2 plates-one positive, one negativeCharge 2 plates-one positive, one negative4.4. Oil droplets acquire extra electron by Oil droplets acquire extra electron by

friction or x-ray irradiationfriction or x-ray irradiation5.5. Oil falls between 2 plates until it stops Oil falls between 2 plates until it stops

falling: positive charge counteracts gravityfalling: positive charge counteracts gravity6.6. How much energy necessary in charged How much energy necessary in charged

plates?plates?

1910: Ernest Rutherford1910: Ernest Rutherford

Gold foil experimentGold foil experiment

Rutherford ModelRutherford Model

The atom had to have something The atom had to have something very dense and positively-charged very dense and positively-charged that was repelling the positive that was repelling the positive alpha particlesalpha particles

1913: Neils Bohr1913: Neils Bohr

Built on discoveries of James Built on discoveries of James Chadwick (the neutron) and Henry Chadwick (the neutron) and Henry Moseley (atomic number = number Moseley (atomic number = number of protons in nucleus)of protons in nucleus)

Proposed an atom with distinct Proposed an atom with distinct energy shells occupied by electrons energy shells occupied by electrons around nucleusaround nucleus

Erwin Schrodinger: Current Erwin Schrodinger: Current ModelModel

Less structured, more uncertaintyLess structured, more uncertainty ““Electron cloud” representing Electron cloud” representing

where electrons are where electrons are most likelymost likely to to be foundbe found

What Do We Know Now?What Do We Know Now?


Structure of atomsStructure of atoms Nucleus: dense cluster, nearly all the Nucleus: dense cluster, nearly all the

atomic massatomic mass Protons: positive chargeProtons: positive charge Neutrons: no chargeNeutrons: no charge

Electron cloud surrounding nucleusElectron cloud surrounding nucleus Negative charge, in distinct patterns of Negative charge, in distinct patterns of

arrangementarrangement Description of elementsDescription of elements

Atomic number: number of protonsAtomic number: number of protons Mass number: number of protons + Mass number: number of protons +

neutronsneutrons Atomic symbol: one or two lettersAtomic symbol: one or two letters

Organization of elementsOrganization of elements IsotopesIsotopes = atoms with the same = atoms with the same

number of protons, but different number of protons, but different numbers of neutronsnumbers of neutrons

Atomic mass = average of the masses Atomic mass = average of the masses of all isotopes of an elementof all isotopes of an element

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NotationNotation

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Electrons orbit the nucleus in discrete Electrons orbit the nucleus in discrete energy levelsenergy levels

Principal quantum numbersPrincipal quantum numbers represent represent energy levelsenergy levels Lowest numbers closest to nucleusLowest numbers closest to nucleusElectrons CANNOT

park between energy levels!


Light behaves as both waves and Light behaves as both waves and particles, and its behavior is due to particles, and its behavior is due to atomic structureatomic structure

Atoms in Atoms in ground stateground state can absorb can absorb energy and kick an electron up to a energy and kick an electron up to a higher energy levelhigher energy level Excited stateExcited state

An electron can ONLY change state An electron can ONLY change state if there is an available higher if there is an available higher quantum levelquantum level Otherwise, incoming energy will not be Otherwise, incoming energy will not be

absorbedabsorbed


• Falling electrons emit photons with wavelengths equal to the amount of energy absorbed

• Energy needed to excite an electron to a higher quantum

level is very specific


For Example…

Organization of the AtomOrganization of the Atom LevelsLevels

Principal quantum number (Principal quantum number (nn)) Higher number = electron energy increasesHigher number = electron energy increases

Number of electrons allowedNumber of electrons allowed 22nn22

Organization of the AtomOrganization of the Atom SublevelsSublevels

The number of sublevels in an energy The number of sublevels in an energy level is equal to the principal quantum level is equal to the principal quantum numbernumber

ss pp dd ff

Increasing energy

Organization of the AtomOrganization of the Atom OrbitalsOrbitals

Theoretical 3-D regions of Theoretical 3-D regions of probabilityprobability Where an electron is most likely to Where an electron is most likely to

existexist Orbital shapesOrbital shapes

ss-orbitals: spherical-orbitals: spherical pp-orbitals: dumbbell shaped (2 lobes)-orbitals: dumbbell shaped (2 lobes)

All orbitals of the same type (e.g. All orbitals of the same type (e.g. ss-orbital) have the same -orbital) have the same shapeshape, , but but volumevolume depends on energy depends on energy levellevel

Hold 2 electronsHold 2 electrons

1s2s

2p3p

Organization of the AtomOrganization of the Atom Farther from the nucleus = higher Farther from the nucleus = higher

energy electronsenergy electrons Filling order depends on energyFilling order depends on energy

Organization of ElementsOrganization of Elements

Read from left to right = order of Read from left to right = order of fillingfilling

Remember: large atoms will fill an Remember: large atoms will fill an ss orbital of the next higher energy orbital of the next higher energy level before filling a level before filling a dd orbital orbital

Review: Atomic OrganizationReview: Atomic Organization

Atomic spectra give us clues about the Atomic spectra give us clues about the organization of electrons around the organization of electrons around the nucleusnucleus

Type of energy given off corresponds to Type of energy given off corresponds to energy levels, sublevels and orbitals of energy levels, sublevels and orbitals of electronselectrons


Electron configuration of oxygen?Electron configuration of oxygen?


Alkali MetalsAlkali Metals Group 1 (1A) on the Group 1 (1A) on the

Periodic TablePeriodic Table Except hydrogen, Except hydrogen,

soft shiny metals soft shiny metals with low melting with low melting pointspoints

Good conductorsGood conductors React vigorously React vigorously

with waterwith water


Alkaline Earth MetalsAlkaline Earth Metals Group 2 (2A) on the Periodic Group 2 (2A) on the Periodic

TableTable Shiny metalsShiny metals Not as reactive with water as Not as reactive with water as

Group 1 elementsGroup 1 elements


HalogensHalogens Group 17 (7A) on the Periodic Group 17 (7A) on the Periodic

TableTable Strongly reactiveStrongly reactive Form compounds with most of Form compounds with most of

the elementsthe elements


Noble GasesNoble Gases Group 8 (8A) on the Periodic Group 8 (8A) on the Periodic

TableTable All gasAll gas Highly non-reactive, seldom in Highly non-reactive, seldom in

combination with other combination with other elementselements


Metals, Metalloids, Non-metals

Quiz YourselfQuiz Yourself

1.1. Convert 116.3 kg into mg. Record the number in Convert 116.3 kg into mg. Record the number in regular and scientific notation.regular and scientific notation.

2.2. Refer to the periodic table and name at least one Refer to the periodic table and name at least one element that is:element that is:

• Noble gasNoble gas• Alkali metalAlkali metal• Alkaline earth metalAlkaline earth metal• HalogenHalogen• Non-metalNon-metal• MetalloidMetalloid

3.3. Write the full and abbreviated electron Write the full and abbreviated electron configuration of:configuration of:

• SiliconSilicon• ManganeseManganese• PotassiumPotassium

4.4. What is the density of a piece of molybdenum that What is the density of a piece of molybdenum that has a mass of 13.2g and a volume of 9.43mL?has a mass of 13.2g and a volume of 9.43mL?

Quiz AnswersQuiz Answers

1.1. 116,300,000116,300,000 1.163 x 101.163 x 1088

2.2. Noble gas = any element in group 18 (8A) on the Noble gas = any element in group 18 (8A) on the Periodic TablePeriodic Table

• Alkali metal = any element in group 1 (1A)Alkali metal = any element in group 1 (1A)• Alkaline earth metal = any element in group 2 Alkaline earth metal = any element in group 2

(2A)(2A)• Halogen = any element in group 17 (7A)Halogen = any element in group 17 (7A)• Non-metal = any noble gas, halogen and O, N, Non-metal = any noble gas, halogen and O, N,

C, P, S, Se, IC, P, S, Se, I• Metalloid = B, Si, Ge, As, Sb, Te, Po, AtMetalloid = B, Si, Ge, As, Sb, Te, Po, At

3.3. Full electron configuration of:Full electron configuration of:• Silicon = 1sSilicon = 1s222s2s222p2p663s3s223p3p22

• Manganese = 1sManganese = 1s222s2s222p2p663s3s223p3p664s4s223d3d55

• Potassium = 1sPotassium = 1s222s2s222p2p663s3s223p3p664s4s11

4.4. 1.40 g/mL1.40 g/mL

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