Periodic Trends

Review - Periodic Law When elements are arranged in order according to their atomic number, certain trends appear. All elements in the same column have very similar properties. All first column elements react with water. Elements in the second column form compounds with elements in Chlorine’s column with the formula MX2

Review - Periodic Table The rows on the periodic table are called either periods or series The columns on the periodic table are called either groups or families The elements at the top of each group are called representative elements.

Review of the Periodic Table Elements Atomic Number Atomic Mass Number Atomic Mass Ion Isotope

Review -Valence Electrons Outermost electrons in an atom Examples: …. The electrons involved in chemical bonding They play a key role in the formation of ions As you go from left to right across the periodic table, the number of valence electrons goes up (except for the transition metals)

Periodic Trends Atomic Radii Ionic Radii Ionization energy Electronegativity Electron affinity Shielding

Atomic Radii The radius of an atom is found from the distance between nuclei in a molecule.

Trends in Atomic Size Size increases going down a column of the periodic table. Size decreases from left to right in a row.

Trends in Atomic Size Cs 6s Rb 5s K 4s Na 3s Li 2s In a family, size increases with the addition of successive electron shells. Example: The alkali metals Cs 6s Rb 5s K 4s Na 3s Li 2s

Ions Ions are atoms that have either gained or lost electrons Cations are positive ions – meaning they have lost electrons Anions are negative ions- meaning they have gained electrons

Ionic Radius vs. Atomic Radius Cations have lost electrons and become smaller than their parent atom There are more protons per electron The pull on the electrons is greater The greater the pull, the smaller the size Anions have gained electrons and become larger than their parent atom There are less protons per electron The pull on the electrons is less

Ionization Energy It takes energy to pull electrons away from elements. The energy required to remove the first electron from an atom is called the first ionization energy I1 The energy required to remove the second electron from an atom is called the second ionization energy I2

Trends in Ionization Energy I1 decreases going down a column of the periodic table. It is easier to pull away electrons that are farther away from the nucleus I1 increases from left to right in a row. It is more difficult to pull electrons away from an atom as the number of protons are increases in the nucleus

Trends in Ionization Energy Arrange the following with increasing ionization energy: C, K, Mg, Na, Ne, Si K < Na < Mg < Si < C < Ne

Valence Electrons Outermost electrons in an atom Examples: …. Often the electrons involved in chemical bonding They play a key role in the formation of ions

Ions Charged Atoms Na+ has 10 e-s Ne has 10 e-s Na+ and Ne are Isoelectronic, meaning they have the same number of electrons

“8 IS GREAT!!!” Atoms are like people…. They like to be as relaxed as possible. Atoms like to exist in as low an energy state as possible Atoms strive to lose or gain electrons to achieve a noble gas configuration…. 8 electrons in the outer shell is the least energetic electron configuration, so elements will lose, or gain electrons to achieve this state

Predicting Ion Charges Predict the most likely charge on the ions of: Li S Ca Cl

Those ODD Transition Metals Many can form multiple ions Ex: Fe2+, Fe3+ These elements are said to be multivalent Fill in most likely charge states on the P.T

Electronegativity The electrons “desire” for its electrons The stronger the electronegativity, the stronger an atom will cling to its electrons Electronegativity increases as you go from left to right on the periodic table Electronegativity increases as you go from bottom to top on the periodic table

Electron Affinity Electron affinity is a measure of the energy that is given off when an atom gains an electron to become an anion Electron affinity increases from bottom to top and from left to right on the periodic table

Shielding Shielding describes the effect of inner electrons reducing the attraction of the nucleus on the outside electrons. The more shells (energy levels), the greater the shielding effect will be. Shielding is why larger atoms have a lower electronegativity, and smaller ionization energies. The protons don’t pull as hard