Valence Electrons • Valence electrons – Electrons in the outer energy level that can be lost, gained, or shared (connected to the group #)
Atomic Radii • The atomic radius is a measure of the size of an atom (½ distance betw 2 nuclei). • The larger the radius, the larger is the atom. • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/atomic4.swf • http://www.youtube.com/watch?v=YS71PbwUPx8
Atomic Radii • Radii decrease across a period because the nucleus gets a larger positive charge • Radii increase down a group because the nucleus gets larger • Which is larger and why? Which is the smallest? Li, O, C, or F • Largest: Li Smallest: F • What about Be, Mg, Ca, or Sr? • Largest: Sr Smallest: Be
Ionization Energy • Ion – an atom that has a positive or negative charge • Ionization – process that results in forming an ion • Ionization energy (IE) – energy required to remove one electron from a neutral atom (energy needed to make a positive charge)
Ionization Energy A + Energy A+ + e- • IE increases across a period because the nuclear charge increases (more electrons in the orbitals) • IE decreases down a group because it is easier to remove e- from higher energy levels
Electron Affinity • Electron Affinity (EA) – energy needed to add an electron to a neutral atom (opposite of IE). A + e- A- + energy
Electron Affinity • EA decreases across periods (get more negative) • EA decreases down groups as nuclear charge increases. ***There are many exceptions to this rule!!!
Ionic Radii • Cation – positive ion (decrease in atomic radii) • Anion – negative ion (increase in atomic radii) • Ionic radii decrease across periods because the electron cloud shrinks • Ionic radii increase down groups as energy levels increase
Electronegativity • Electronegativity -- the ability of an atom to attract electrons • Electronegativities increase across a period and decrease down groups (but there are exceptions!) **Fluorine is the most electronegative atom!!
The Best Way to Remember…. • Just know all the trends that surround Fluorine, and work your way down or across! • F – most electronegative, highest IE, lowest EA, small atomic and ionic radii