Elemental Properties and Patterns

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

  The full, positive nuclear charge is “SHIELDED” from outer shell electrons by all the other electrons between them  Electrons closer to the nucleus shield other electrons further away.  Full attractive force is not felt by outer electrons  Electrons have different energies and therefore, located at different regions surrounding the nucleus  Based on electrostatic field + positively charged nucleus Electron Shielding

  The amount of nuclear charge influencing or attracting an electron  = actual nuclear charge—screening influence of other electrons Effective Nuclear Charge (Z eff )

  An atom’s size affects chemical and physical properties of an atom  Atom’s size is related to the radius of the atom  Radius of atom = ½ distance between nuclei of 2 adjacent atoms of the same element  Radius is the distance from the center of the nucleus to the “ edge ” of the electron cloud.  half the distance between the nuclei of 2 bonded atoms. Atomic Radii

 Atomic Radius General Trend Decreases Increases

 Atomic 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— MOVING ACROSS TABLE  More and more electrons are added and placed at higher and higher energy levels so atomic size increases— MOVING DOWN TABLE

  Half the distance between nuclei of adjacent atoms in a metal  Radius of metallic atoms  > 75% of elements are metals 1. Metallic Radii

 2. Covalent Radius  Half the distance between the nuclei of 2 adjacent, bonded atoms in a chemical compound.  Atoms MUST be identical  Radius of nonmetallic atoms (Ex. Cl 2. Br 2 )  Smaller radii than metallic—covalent bonds hold the atoms close  Ex. Br Å 1.43 Å

  Ions  Atoms that have gained or lost electrons ( anion, cation )  Electrons gained/lost from valence shell (outer electron shell)  Defined by the distance between the nuclei of 2 ions  Studies with crystal structures  Radii related to original atomic radii Ionic Radii

 1) Anions  LARGER size than original neutral atom  Generally nonmetals  Additional electrons cause the atom’s size to increase  Electrons repel as increase in number, causes size to increase Ionic Radii (cont.)

 2) Cations  SMALLER size than original neutral atom  Generally metals  Removal of electrons causes the atom’s size to decrease  more attractive force from nucleus, nucleus can pull remaining electrons towards it. Ionic Radii (cont.)

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  Compare atomic sizes of Na and Cl  NeutralIon Na > Cl Na + < Cl - Example 1

  Applies to either atoms or ions  Atoms or ions with the SAME number of electrons  So electron configuration is the same as well  Does not state the protons stay the same  As the proton number increases but the electrons stay the same, the positive nucleus holds electrons more tightly Isoelectric

 Atom/IonRadius (nm)Electron Configuration O s 2 2s 2 2p 6 F-F s 2 2s 2 2p 6 Ne0.1121s 2 2s 2 2p 6 Na s 2 2s 2 2p 6 Mg s 2 2s 2 2p 6

  Which of the following ions has the LARGEST radius? A) Na+ B) Mg +2 C) S 2- D) Cl - E) Se 2- Example 2:

  Which of the following ions has the SMALLEST radius? Why? A) K + B) Li + C) Be +2 D) O 2- E) F - Example 3:

  Which of the following isoelectric ions is the LARGEST? Why? A) Mn +7 B) P 3- C) S 2- D) Sc 3+ E) Ti 4+ Example 4:

  Atomic Theory III Worksheet #1-17 Homework