PES  Provides explanation for shells and orbitals in quantum theory  Photoelectric effect —  Utilization of photons to remove electrons from atoms  Photons have been energized, analyzing the energy needed to remove electrons from an atom/compound  Photoelectric spectrum —  Energy on x-axis  Number of electrons in a subshell on y axis

Photoelectric SpectrumPhotoelectric Spectrum  Peaks —  Number of subshells/orbitals  Peak heights —  Number of electrons in subshell  Electrons within the same subshell have similar energy values but different orbital energies, energy values vary among subshells  Shells with high energies indicate electrons located close to nucleus

Example 1: NaExample 1: Na

Example 2:Example 2:  A third period element in the periodic table forms a PES spectrum with three peaks, in the ratio 2:2:1. Name this element. A)Aluminum B)Boron C)Carbon D)Sodium

Example 3:Example 3:  Aluminum has the following electron configuration: 1s 2 2s 2 2p 6 3s 2 3p 1 A)How many peaks should be expected in a PES spectrum for Al? B)Which electrons will show the highest energies? Why?

Example 3: (cont.)Example 3: (cont.)  Aluminum has the following electron configuration: 1s 2 2s 2 2p 6 3s 2 3p 1 C) Which peak on the spectrum will be the most intense/largest? Why? D) Explain why the peaks for the 3s and 3p electrons would be closely grouped and why they are different than electrons in the 2s and 2p orbitals.

The Periodic LawThe Periodic Law  Dimitri Mendeleev (1869/1871) was the first scientist to publish an organized periodic table of the known elements.  He was taking a chemistry course in Russia and tried to find a way to organize the periodic table.

The Periodic LawThe Periodic Law  Mendeleev even went out on a limb and predicted the properties of 2 at the time undiscovered elements.  He was very accurate in his predictions, which led the world to accept his ideas about periodicity and a logical periodic table.

The Periodic LawThe Periodic Law  Mendeleev understood the ‘ Periodic Law ’ which states:  When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.

The Periodic LawThe Periodic Law  Atoms with similar chemical properties and behavior appear in groups or families (vertical columns named by Roman numerals with A or B) on the periodic table.  They are similar because they all have the same number of valence (outer shell) electrons, which governs their chemical behavior.  Periods– horizontal rows on periodic table

Periodic TrendsPeriodic Trends  There are several important atomic characteristics that show predictable trends that you should know.  Atomic properties—  Deal with only single atoms

Atomic RadiusAtomic Radius  Enables us to gain information on atom’s size  Outer electrons hard to locate  Radius is the distance from the center of the nucleus to the “ edge ” of the electron cloud.  Measurement of distance between nuclei of 2 atoms  Since a cloud ’ s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms.

1. Covalent Radius1. Covalent Radius  Half the distance between the nuclei of 2 bonded atoms.  Radius of nonmetallic atoms  Ex. Br 2.86 Å 1.43 Å

 Half the distance between nuclei of adjacent atoms in a metal  Radius of metallic atoms 2. Metallic Radius2. Metallic Radius

Atomic Radius TrendAtomic Radius Trend Decreases Increases

Atomic RadiusAtomic Radius  The effect is that the more positive nucleus has a greater pull on the electron cloud.  The nucleus is more positive and the electron cloud is more negative.  The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.

Identify the atom with the largest radii  1) Ca, F  2) Cl, O  3) N, P

 Affected by distance between nuclei of 2 ions  Defined by the distance between the nuclei occupied by the particular ion  Studies with crystal structures  Radii related to original atomic radii  Isoelectronic—  Atoms/ions with SAME number of electrons SO electron configuration same as well Ionic RadiiIonic Radii

 Larger size than original neutral atom  Generally nonmetals  Electrons repel as increase in number, causes size to increase Ionic Radii: 1) AnionsIonic Radii: 1) Anions

 Smaller size than original neutral atom  Generally metals  Less electrons, more attractive force from nucleus Ionic Radii: 2) CationsIonic Radii: 2) Cations

Ionization EnergyIonization Energy  If an electron is given enough energy (in the form of a photon) to overcome the effective nuclear charge holding the electron in the cloud, it can leave the atom completely.  Amount of energy needed to remove ONE electron from a neutral atom  Removal from ground state in neutral atom of gaseous state to form positive ion

Ionization Energy (cont.)Ionization Energy (cont.)  The energy required to remove an electron from an atom is ionization energy.  The larger the atom is, the easier its electrons are to remove.  Ionization energy and atomic radius are inversely proportional.

 1 st ionization energy  Energy required to remove 1 st electron from atom  Taken from highest energy level  Easiest to remove  Energy increases as more electrons are removed Ionization Energy (cont.)Ionization Energy (cont.)

Ionization Energy TrendIonization Energy Trend Increases Decreases

Ionization EnergyIonization Energy

Identify the highest ionization energy 1)F, Mg 2)Na, Rb 3)P, O

What does affinity mean?

Electron AffinityElectron Affinity  energy change that occurs when electrons added to gaseous atom  Greater value with smaller atoms  Energy released when electron added  Exothermic, negative value  An atom’s “desire/affinity” for more electrons, wants to get more electrons ! ! !  Metals—decrease electron affinity.  Nonmetals—increase electron affinity, more reactive  Stable atoms—full octet

Electron Affinity TrendElectron Affinity Trend Increases Decreases

Metals, Nonmetals, Metalloids  How can you identify a metal?  What are its properties?  What about the less common nonmetals?  What are their properties?  And what the heck is a metalloid?

A Different Type of Grouping  Besides the 4 blocks of the table, there is another way of classifying element:  Metals  Nonmetals  Metalloids or Semi-metals.  The following slide shows where each group is found.

Metals  Metals are shiny, malleable, ductile, and are good conductors of heat and electricity.  They are mostly solids at room temp.  Want to LOSE valence electrons  Form positive ions  s block (not H and He), d/f blocks, some p block elements

Nonmetals  Nonmetals are the opposite.  No color, no shine  They are dull, brittle, nonconductors ( insulators ).  Gases at room temperature  Want to GAIN electrons  Form negative ions  p block elements, H and He

Transition MetalsTransition Metals  Middle of the periodic table  Forms positive ions, multiple types  Shine, malleable, ductile, good conductors  s/d orbitals—electrons lost from these subshells.

Metalloids/Semi-Metals  Metalloids, aka semi-metals are just that.  They have characteristics of both metals and nonmetals.  They are shiny (like metals) but brittle.  And they are semiconductors.  “on the fence, middle of the road”  B, Si, As, Te, At, Ge, Sb, Po

Noble GasesNoble Gases  Group 18  Do NOT react with other elements  Atomspheric gases  Naturally in elemental form, single atoms  Not completely unreactive

Metallic CharacterMetallic Character  This is simply a relative measure of how easily atoms lose or give up electrons.  Tendency to LOSE electrons  Related to atomic radius/ionization energy, how easy to remove electrons

Metallic CharacterMetallic Character Decreases Increases

 Atoms with a tendency to GAIN electrons Nonmetallic CharacterNonmetallic Character Increases Decreases

Classwork: Ionization Energy Circle the atom with the highest first ionization energy. 1)Al, B5) Fr, Li9) Se, Cl 2)Mg, Na6) Mg, Al10) Rb, Mg 3)P, As7) C, F 4)I, At8) K, Sc

Classwork: Metal IdentityClasswork: Metal Identity Identify each element as a nonmetal, metal, or metalloid 1)Na6) Cl 2)P7) Mg 3)Se8) Al 4)Ge9) Sb 5)N10) Si