Periodic Trends

Trends in Atomic Size Atomic Radius –Half of the distance between the nuclei of two atoms of the same element when the atoms are bonded together –Half the distance between two atoms of Oxygen in O 2 will be the atomic radius of an Oxygen atom. Distance between nuclei Nucleus Atomic

Why? Periods: More protons can pull electrons closer to nucleus –Energy level stays the same Groups: More energy levels so electrons are farther away from the nucleus –A “shield” is created protecting the electrons from being pulled in tighter by the protons –“Shielding Effect”

Which atom has the smallest radius? –Li or B? –Na or Cs?

Ions An atom or group of atoms that has a positive or negative charge Positive and negative ions form when electrons are transferred between atoms

Cation When an atom LOSES an electron it must have more protons than electrons so it will have an overall POSITIVE charge.

Anion If an atom GAINS an electron it will have an overall NEGATIVE charge. This is because they contain more electrons than protons.

Trends in Ionic Size Cations are always smaller than the atoms from which they form… Why? Anions are always larger than the atoms from which they form… Why?

Which atom has the larger radius? –Na or Na +1 –O or O -2

Trends in Ionization Energy Ionization Energy –Process of forming an ion –The amount of energy it takes to remove one valence electron from a neutral atom. –Needs energy in order for this to happen

Why? Easy for element with only 1 or 2 valence electrons to lose them and then drop an energy level All atoms want an OCTET - 8 electrons in outermost energy level  takes the configuration of noble gas = stable Atoms can have multiple ionization energies

Which atom has a higher ionization energy? –Ba or Ca? –Ne or F?

Trends in Electronegativity Electronegativity –The tendency of atoms to accept electrons –Atoms want an octet in their outermost energy level (takes the configuration of a stable noble gas) Increases as you go from left to right across the periodic table Decreases as you go down the periodic table - Why? It’s easier for atoms with 6 or 7 valence electrons to grab a few in order to make an octet. Elements with more energy levels have more “shield” so protons cannot pull electrons What about Noble Gases? What is the most electronegative element?

Which element has the highest electronegativity? –K or Li? –Fe or Br? –Na or Al?

Electron Affinity Energy released when an electron is added to a neutral atom (kJ/mole) Opposite of ionization energy