Chapter 5 – Modern Chemistry Periodic Law Chapter 5 – Modern Chemistry

5.1 History of the Periodic Table Dmitri Mendeleev Created with the first periodic table Organized it according to atomic mass Discovered that the table exhibited chemical periodicity Repeating pattern of chemical properties Correctly stated as periodic law

History of the Periodic TAble Henry Mosley Reorganized table according to atomic number His work also led to the modern definition of the atomic number Working with Ernest Rutherford

Modern Table Noble Gases Lanthanides Actinides John William Strutt and Sir William Ramsey discovered argon and helium Discovered from line emission spectrums from the sun Led to Group 18 Lanthanides Early 1900’s Discovery in Ytterby Actinides Final piece to the table Many man made elements

5.2 Electron Configuration

S and P block S block P block Groups 1 and 2 Period is the same as the principle energy level P block Groups 13 – 18 These two blocks make up the outer most configuration (valence shell) of the element

D and F Block D block F block Groups 3-12 (Transition Metals) Electrons fall into an interior shell Period – 1 is equal to the principle energy level F block Inner Transition Metals Electrons also fall into interior shells Period – 2 is equal to the principle energy level

5.3 Periodic Trends Atomic Size (Radius) Periods (moving left to right) Decrease Due to a lessening of the shielding effect Shielding effect is a phenomena in which the interior electrons will ”shield” the pull of the nucleus from the outer most electrons As more and more outer electrons are added to the valence shell, it becomes harder for the interior electrons to ”shield” the outer electrons This causes the energy level to be pulled closer to the nucleus Groups (top to bottom) Increase Due to increase in outer energy levels

Periodic Trends Ionization Energy Ionization is the process of atoms forming ions to fulfill the octet rule Ionization Energy is the energy associated with removing electrons Periods Increase (harder to remove electrons) Result of a lessening of the shielding effect Nucleus has a greater pull on the outer most electrons Groups Decrease Further from the nucleus due to increase in energy levels

Periodic Trends Ionic Size (Radius) Depends on the type of ion that is formed Positive Ions (Groups 1, 2, and 13) Positive Ions are formed by losing electrons Group 1 loses 1 electron, group 2 loses 2 electrons, and group 13 loses 3 electrons More electrons that are lost the greater the positive charge and the stronger the pull of the nucleus Decrease in size from groups 1 to 13

Periodic Trends Ionic Size (Radius) Negative ions (Groups 15, 16, and 17) Negative ions are formed by gaining electrons Group 15 gains 3, group 16 gains 2, and group 17 gains 1 The more electrons that are gained the further the cloud can pull away from the nucleus Decrease in size from group 15 to 17

Periodic Trends Ionic Size Increases down a group Doesn’t matter whether it is positive or negative Increase is still a result of an increase in outer energy level Comparing Ionic size and Atomic size Smallest to largest across a period Metal ion < nonmetal atom < metal atom < nonmetal ion

Periodic Trends Electron Affinity Energy change associated when an atom gains an electron (negative energy value) Can also be defined as the energy when a negative ion loses an electron (positive energy value) Periods Increase Explained by the octet rule Groups Decrease Increase in energy level in which size affects affinity

Periodic Trends Electronegativity This is the ability of an atom when forming a covalent bond to draw the shared electrons closer to its own nucleus Periods Increase Due to a lessening of the shielding effect Groups Decrease Due to the outer most electrons getting further from the nucleus

Periodic Trends Valence Electrons Group 1 – 1 valence