Of Atoms and Elements Historical and Modern Perspectives

1831: Michael Faraday Discovery of ions Discovery of ions Anion : negatively-charged particles Anion : negatively-charged particles Cation : positively-charged particles Cation : positively-charged particles Science of electrolysis: splitting substances using electricity Science of electrolysis: splitting substances using electricity Determined that atoms were electrical in nature Determined that atoms were electrical in nature

1895: Wilhelm Roentgen Studying glow produced from cathode rays Studying glow produced from cathode rays Noticed that the glow could be transmitted to chemically-treated paper Noticed that the glow could be transmitted to chemically-treated paper X-rays discovered, but not fully understood X-rays discovered, but not fully understood

1895: Antoine Bequerel Photographic film fogged when placed close to samples of uranium Photographic film fogged when placed close to samples of uranium Required no input of energy Required no input of energy Graduate student Marie Curie and later her husband Pierre continued to study the phenomenon Graduate student Marie Curie and later her husband Pierre continued to study the phenomenon Marie coined the term “radioactivity” Marie coined the term “radioactivity”

1897: Joseph John Thomson Showed that the beam created in a cathode-ray tube was attracted to a positive plate and repelled by a negative plate Showed that the beam created in a cathode-ray tube was attracted to a positive plate and repelled by a negative plate The particles were the same regardless of the material from which the ray was generated The particles were the same regardless of the material from which the ray was generated Coined the term “electrons” for the negative particles Coined the term “electrons” for the negative particles

Thomson’s Experiment Image source:

Thomson’s Model Realized that the negatively-charged particles had to be balanced by a positively-charged substance Realized that the negatively-charged particles had to be balanced by a positively-charged substance “Plum Pudding Model” “Plum Pudding Model” Image sourcehttp://mws.mcallen.isd.tenet.edu/mchi/ipc/ch05htm/ch05sec1.htm

1909: Robert Millikan Received Nobel Prize in 1923 for work Received Nobel Prize in 1923 for work Calculated mass and charge of electrons Calculated mass and charge of electrons Mass = kg Mass = kg Image source:

Millikan’s Experiment 1. Sprayed oil droplets into a chamber 2. Calculated mass of droplets by how fast they fall (gravity) 3. Charge 2 plates-one positive, one negative 4. Oil droplets acquire extra electron by friction or x-ray irradiation 5. Oil falls between 2 plates until it stops falling: positive charge counteracts gravity 6. How much energy necessary in charged plates?

1910: Ernest Rutherford Gold foil experiment Gold foil experiment Image source: source:

Rutherford Model The atom had to have something very dense and positively-charged that was repelling the positive alpha particles The atom had to have something very dense and positively-charged that was repelling the positive alpha particles Image source:

1913: Neils Bohr Built on discoveries of James Chadwick (the neutron) and Henry Moseley (atomic number = number of protons in nucleus) Built on discoveries of James Chadwick (the neutron) and Henry Moseley (atomic number = number of protons in nucleus) Proposed an atom with distinct energy shells occupied by electrons around nucleus Proposed an atom with distinct energy shells occupied by electrons around nucleus Image source: source:

Erwin Schrodinger: Current Model Image source: Less structured, more uncertainty Less structured, more uncertainty “Electron cloud” representing where electrons are most likely to be found “Electron cloud” representing where electrons are most likely to be found

What Do We Know Now?

Structure of atoms Structure of atoms Nucleus: dense cluster, nearly all the atomic mass Nucleus: dense cluster, nearly all the atomic mass Protons: positive charge Protons: positive charge Neutrons: no charge Neutrons: no charge Electron cloud surrounding nucleus Electron cloud surrounding nucleus Negative charge, in distinct patterns of arrangement Negative charge, in distinct patterns of arrangement Description of elements Description of elements Atomic number: number of protons Atomic number: number of protons Mass number: number of protons + neutrons Mass number: number of protons + neutrons Atomic symbol: one or two letters Atomic symbol: one or two letters

Organization of elements Organization of elements Isotopes = atoms with the same number of protons, but different numbers of neutrons Isotopes = atoms with the same number of protons, but different numbers of neutrons Atomic mass = average of the masses of all isotopes of an element Atomic mass = average of the masses of all isotopes of an element Image source: What Do We Know Now?

Notation Notation wps.prenhall.com What Do We Know Now?

Electrons orbit the nucleus in discrete energy levels Electrons orbit the nucleus in discrete energy levels Principal quantum numbers represent energy levels Principal quantum numbers represent energy levels Lowest numbers closest to nucleus Lowest numbers closest to nucleus Electrons CANNOT park between energy levels! What Do We Know Now?

Light behaves as both waves and particles, and its behavior is due to atomic structure Light behaves as both waves and particles, and its behavior is due to atomic structure Atoms in ground state can absorb energy and kick an electron up to a higher energy level Atoms in ground state can absorb energy and kick an electron up to a higher energy level Excited state Excited state An electron can ONLY change state if there is an available higher quantum level An electron can ONLY change state if there is an available higher quantum level Otherwise, incoming energy will not be absorbed Otherwise, incoming energy will not be absorbed What Do We Know Now?

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 What Do We Know Now? For Example…

Organization of the Atom Levels Levels Principal quantum number (n) Principal quantum number (n) Higher number = electron energy increases Higher number = electron energy increases Number of electrons allowed Number of electrons allowed 2n 2 2n 2

Organization of the Atom Sublevels Sublevels The number of sublevels in an energy level is equal to the principal quantum number The number of sublevels in an energy level is equal to the principal quantum number s p d f Increasing energy

Organization of the Atom Orbitals Orbitals Theoretical 3-D regions of probability Theoretical 3-D regions of probability Where an electron is most likely to exist Where an electron is most likely to exist Orbital shapes Orbital shapes s-orbitals: spherical s-orbitals: spherical p-orbitals: dumbbell shaped (2 lobes) p-orbitals: dumbbell shaped (2 lobes) All orbitals of the same type (e.g. s-orbital) have the same shape, but volume depends on energy level All orbitals of the same type (e.g. s-orbital) have the same shape, but volume depends on energy level Hold 2 electrons Hold 2 electrons 1s2s2p3p1s2s2p3p Image source:

Organization of the Atom Farther from the nucleus = higher energy electrons Farther from the nucleus = higher energy electrons Filling order depends on energy Filling order depends on energy

Organization of Elements Read from left to right = order of filling Read from left to right = order of filling Remember: large atoms will fill an s orbital of the next higher energy level before filling a d orbital Remember: large atoms will fill an s orbital of the next higher energy level before filling a d orbital

Review: Atomic Organization Atomic spectra give us clues about the organization of electrons around the nucleus Atomic spectra give us clues about the organization of electrons around the nucleus Type of energy given off corresponds to energy levels, sublevels and orbitals of electrons Type of energy given off corresponds to energy levels, sublevels and orbitals of electrons

Organization of Elements Electron configuration of oxygen? Electron configuration of oxygen?

Organization of Elements Alkali Metals Alkali Metals Group 1 (1A) on the Periodic Table Group 1 (1A) on the Periodic Table Except hydrogen, soft shiny metals with low melting points Except hydrogen, soft shiny metals with low melting points Good conductors Good conductors React vigorously with water React vigorously with water

Organization of Elements Alkaline Earth Metals Alkaline Earth Metals Group 2 (2A) on the Periodic Table Group 2 (2A) on the Periodic Table Shiny metals Shiny metals Not as reactive with water as Group 1 elements Not as reactive with water as Group 1 elements

Organization of Elements Halogens Halogens Group 17 (7A) on the Periodic Table Group 17 (7A) on the Periodic Table Strongly reactive Strongly reactive Form compounds with most of the elements Form compounds with most of the elements

Organization of Elements Noble Gases Noble Gases Group 8 (8A) on the Periodic Table Group 8 (8A) on the Periodic Table All gas All gas Highly non-reactive, seldom in combination with other elements Highly non-reactive, seldom in combination with other elements

Organization of Elements Metals, Metalloids, Non-metals

Quiz Yourself 1. Convert kg into mg. Record the number in regular and scientific notation. 2. Refer to the periodic table and name at least one element that is: Noble gas Noble gas Alkali metal Alkali metal Alkaline earth metal Alkaline earth metal Halogen Halogen Non-metal Non-metal Metalloid Metalloid 3. Write the full and abbreviated electron configuration of: Silicon Silicon Manganese Manganese Potassium Potassium 4. What is the density of a piece of molybdenum that has a mass of 13.2g and a volume of 9.43mL?

Quiz Answers ,300, x Noble gas = any element in group 18 (8A) on the Periodic 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 (2A) Alkaline earth metal = any element in group 2 (2A) Halogen = any element in group 17 (7A) Halogen = any element in group 17 (7A) Non-metal = any noble gas, halogen and O, N, C, P, S, Se, I Non-metal = any noble gas, halogen and O, N, C, P, S, Se, I Metalloid = B, Si, Ge, As, Sb, Te, Po, At Metalloid = B, Si, Ge, As, Sb, Te, Po, At 3. Full electron configuration of: Silicon = 1s 2 2s 2 2p 6 3s 2 3p 2 Silicon = 1s 2 2s 2 2p 6 3s 2 3p 2 Manganese = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 Manganese = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 Potassium = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Potassium = 1s 2 2s 2 2p 6 3s 2 3p 6 4s g/mL