Chemistry - SCH3U - Unit 1 - Atomic Theory & Periodic Trends

How model of early atomic structure theories developed

• Emperial knowledge

• Theoretical knowledge

• Theories

Emperial knowledge

• Observations/data

Theoretical knowledge

• Ideas from observations

Theories

• Describe observations in term non-observable idea

• Explain using idea and model

• Perdict result

• Simple as possible

• Are dynamic

Democritus when

• 400 B.C.

Democritus

• 400 B.C.

• Matter compose tiny particle

• Keep splitting matter constantly will reach point where can not keep going

• Atomos = uncuttable

• Atoms different size, constant motion, seperate empty space

• Every matter is made of that particle

Who reject Democritus theory

Aristotle reject

Aristotle when

• 350 B.C

Thought all matter made of Earth, Fire, Air, Water

• Aristotle

Aristotle

• 350 B.C.

• Reject Democritus theory

• All matter made of Earth, Fire, Air, Water

• Each basic substance from combination four specific qualities

  • Cold, dry, hot, moist

• Accepted for ~2000 years

Dalton when

• 1800

Developed billiard model

• Dalton model

Dalton

• 17th-18th centuries brought scientific revolution

  • Emphasis on scientific method and evidence

• Billiard ball model (atom as solid sphere)

  • All matter composed tiny indivisible particle called atom

  • All atom of same element have identicle properties

  • Atom of different element have different properties

  • Atom of two or more element can combine in constant ration to form new substances

  • In chemical reactions, atom join or seperate but are not destroyed

    • Law of conservation of mass

  • Did not account for how electrical charges were acquired

JJ Thomson when

• 1897

Cathode ray tube experiment who

• JJ Thomson experiment

Plum pudding/rasin bun model

• JJ Thomson model

Cathode ray tube experiment

• See if ray has electrical charge

• Test charge of ray using opposite charged charge plate and magnet

  • Turned away from negative and towards positve

• Conclude must have negative charge

• Particle that make up cathode ray tube 1000 time smaller then hydrogen atom

• Different mental get same cathode ray tube

How much smaller are particle make up cathode ray tube compare hydrgoen atom

• 1000 time smaller

JJ Thomson

• Invented cathode ray tube

• Propose idea of subatomic particles

• First to hypothesize electron

• Electrons, negative charge

• Suggest negative electron embedded of surface of positive charge sphere

  • Mostly empty space

  • Plum pudding model

  • Rasin bun model

• Cathode ray tube experiment

  • See if ray has electrical charge

  • Test charge of ray using oppositce charged charge plate and magnet

    • Turned away from negative and towards positve

  • Conclude must have negative charge

  • Particle that make up cathode ray tube 1000 time smaller then hydrogen atom

  • Different metal get same cathode ray tube

Nagaoka when

• 1903

Nagaoka

• Represented atom as positive charge sphere with ring of negative charge electron

• Saturnian model

Saturnian model

• Nagaoka model

Thought Thomson correct

• Rutherford

Rutherford when

• 1903

Gold foil experiment who

• Rutherford experiment

Gold foil experiment

• Shot alpha (x) particle (tiny positively charged, smaller then atom) through thin gold foil

• If Thomson model correct, particles would pass through

  • As atom mostly empty space

• Most did but some did not

  • Found atom have nucleus that occasionally cause alpha particle bounce back

    • Something hard inside atom or something same charge as alpha (x) particle

• Conclude

  • Nuclues positive charge + contain majority atom mass

  • Atom mostly empty space

  • Electron orbit nucleus

    • Float near nucleus

      • No belief of orbital shells yet

Rutherford

• Thought Thomson corrrect

  • Wanted test Thomson theory

• Gold foil experient

  • Shot alpha (x) particle (tiny positively charged, smaller then atom) through thin gold foil

  • If Thomson model correct, particles would pass through

    • As atom mostly empty space

  • Most did but some did not

    • Found atom have nucleus that occasionally cause alpha particle bounce back

      • Something hard inside atom or something same charge as alpha (x) particle

  • Conclude

    • Nucleus positive charge + contain majority atom mass

    • Atom mostly empty space

    • Electron orbit nucleus

      • Float near nucles

        • No belief of orbital shells yet

• Protons

Chadwhich

• Demonstrated nuclei must contain heavy neutral particles as well as proton

  • Called them neutron

Chadwhich when

• 1932

Limitation Rutherford model

• Why electron not go to nucleus

• What keep them from escaping and traveling out of barrier

• What keep proton so close together if like charges repel

Bohr model

• Electron are confined in energy level

• Fixed distances from nucleus

• Electrons in same orbit have energy

  • Closer = less energy

  • Further = more energy

• Electron do not exist between energy level

• Always occupy lowest possible energy level

  • Can not just skip first shell and fill next

• Max electron in energy level is 2n²

  • Where n is energy level

Evidence of Bohr model

• Line spectrum

  • When atom of element heated will release set distinct colour

  • Lines of colour are called line spectrum

  • Each element has own unique line spectrum

  • Each colour has distinct amount energy

    • Red = lowest

    • Purple = highest

• Connecting evidence to model

  • Electron absorb energy when heated

  • If enough heat added, electron can jump to higher energy level

    • Excited state

  • When energy is lost will fall back down

    • Ground state

  • Energy lost is released as light to give distinct colour

  • Line spectrum represent transition from excited to ground state

• NOTE

  • Even though Hydrogen only one electron will not have just one atom

    • Different atom may get different amount energy

When electron jump higher energy level is in _____ state

• Excited state

When electron lose energy fall back down is in _____ state

• Ground state

When electron lose energy, energy is release as

• Energy lost is released as light to give distinct colour

Isotope

• 2 or more atom of same element with different atomic mass

• Due to different number of neutron within nuclei

Isotope similarities

• Same proton and electron

• Same appearance and chemical properties

  • Different if isolate single isotope

Isotope differences

• Different neutron

• Different atomic mass

Isotopic abundance is _____

• Isotopic abundance is fixed

  • Every sample of the element has same proportions of isotopes

Average atomic mass on periodic table

• Average atomic mass (on periodic table) is weighted average of all isotope masses

• Takes into account isotope masses and percent abundances

• In weighted average calculation isotope with greatest percentage has biggest influence on average atomic mass

What has greatest influence on average atomic mass

• In weighted average calculation isotope with greatest percentage has biggest influence on average atomic mass

Average atomic mass formula

• AAM(u) = (%ab_1 x mass_1 ) + (%ab_2 x mass_2 ) + . . . (%ab_{n} x mass_{n} )

AAM

• Average atomic mass

u

• Unified atomic mass unit

%ab

• Percent abundance (put into decimal)

m

• Mass of isotope

Radioisotope

• Unstable isotopes

• Produce nuclear radiation as decay and become radioactive

Alpha radiation

• Same nucleus as He(2p,2n,+2)

• Relatively slow

• Travel through air a few cm

• Effective barrier of sheet of paper

Beta radiation

• e^- 

• Relatively fast

• Travel through air a few m

• Effective barrier of 1-2mm of metal

Gamma radiation

• No mass high energy electromagnetic rod more wave then particle

• Speed of light

• Travel through air is unlimited

• Effective barrier of 1m lead or concrete

Half-life

• Time take for one-half originial radioactive atom to decay

• Vary between isotopes (cs-142 = 5×10^{15} years vs Polonium-216 = 0.16 seconds)

Forces within atom

• Forces of attraction with nucleus

• Forces of repulsion with other electrons

Core charge

• How measure force attraction of nucleus on valence electron

Core charge formula

• CC = #p - #inner e

In uncharged atoms core charge is same as _____

• Core charge is same as number valence electron in uncharged atom

Electron shielding

• Measure force of repulsion between electron

How measure electron shielding

• Measure by number of full shell electron

Atomic radius down group

• Increases down a group

  • Force of repulsion increases

    • From adding shells

  • No change force attraction

Atomic radius left to right across period

• Decreases moving right

  • Force of attraction increases

    • From adding electrons to existing shells

  • No change force repulsion

Ionic radius

• Groups 1, 2, 13-18

  • Cations always smaller than original (core charge increases)

  • Anions always larger than original (newly completed electron shell)

Ionization energy

• Energy required remove electron

IE

• Ionization energy

FA

• Force of attraction

cc

• Core charge

Zeff

• Effective nuclear charge

FR

• Force of repulsion

es

• Electron shielding

Energy trends

• Ionization energy

• Electron affinity

• Electronegativity

Ionization energy trend

• Ionization energy down, down group

  • Increase repulsive force

  • Valence e are farther away from nucleus

• Ionization energy up, left-right period

  • Increase core charge

  • More difficult pull away an e

EA

• Electron affinity

Electron affinity

• Energy released when atom gain electron

Electron affinity trend

• Electron affinity down, down group

  • More repulsive force mean difficult to add electron

  • Less energy release when electron added

• Electron affinity up, left-right period

  • Core charge increase

  • More energy release when electron added

Electronegativity

• Tendancy for atom to pull bonding electron toward itself

General trend up periodic table

• Ionization and electron affinity increase

• Atomic radius decrease

General trend down periodic table

• Ionization and electron affinity decrease

• Atomic radius increase

General trend left periodic table

• Ionization and electron affinity decrease

• Atomic radius increase

General trend right periodic table

• Ionization and electron affinity increase

• Atomic radius decrease