Dimitri Mendeleev-organized the first periodic table—arranged in order of increasing atomic mass; found gaps which he predicted were elements that existed but hadn’t been discovered yet Henry Mosely- organized the periodic table according to increasing atomic number. This is the periodic table we use today.

Groups/Families- are COLUMNS on the periodic table Periods/Energy levels- are ROWS on the periodic table Noble Gases = 8A, full s and p sublevels Representative Elements = 1-7A, partially full s and p Transition Elements = group B, partially filled s and d Inner Transition elements = separate block, partially filled s and f sublevels

Radius- distance between the nucleus and outermost shell. Determined indirectly by measuring distance between the two nuclei of a diatomic molecule and dividing by 2

Ionization Energy- the energy required to remove a valence electron from an Atom (costs energy) Electron Affinity- the energy change associated with gaining an electron (usually energy released) Electronegativity- the tendency for an atom to draw electrons to itself in a chemical bond.

Valence Electrons- are the outermost electrons, in the highest energy level. Atoms within a group have the same number of valence electrons, equal to the column number (representative elements only). Core electrons- inner electrons. These electrons block the valence electrons from the attraction of the nucleus.

VALENCE ELECTRONS CORE ELECTRONS

Radius-gets smaller Ionization energy-gets BIGGER Electron affinity-gets BIGGER Electronegativity-gets BIGGER

Radius-gets LARGER Ionization energy-gets smaller Electron affinity-gets smaller Electronegativity-gets smaller

EFFECTIVE NUCLEAR CHARGE (ENC)- the attraction a valence electron feels toward the nucleus. It is affected by the number of core electrons. THE ENC INCREASES ACROSS A PERIOD

The radius (atomic size) decreases The ionization energy increases (the stronger the bond, the more energy must be used to remove an electron) The electron affinity increases (new electrons go into shells that are closer to the nucleus, resulting in a stronger bond) The electronegativity increases (same reason)

SHIELDING EFFECT- core electrons shield valence electrons from the attraction of the nucleus. More core electrons = more shielding = less of a bond between the nucleus and valence electrons SHIELDING INCREASES DOWN A GROUP

MORE CORE ELECTRONS >> BLOCK NUCLEUS >> LESS ATTRACTION… WEAKER BOND! Radius increases Ionization energy decreases (easier to remove valence electron) Electron Affinity decreases (new electrons go into energy levels further from the nucleus, where there is little attraction) Electronegativity decreases (same reason)

When an atom becomes a cation (loses electron, positive charge) it’s radius gets smaller (nucleus pulls tighter on remaining electrons). When an atom becomes an anion (gains electron, negative charge) its radius gets larger (more electrons = more repulsion between them).

1 ST IONIZATION ENERGY= ENERGY TO REMOVE 1 ELECTRON 2 ND IONIZATION ENERGY = ENERGY TO REMOVE 2 ND 3 RD IONIZATION ENERGY= 3 RD …ETC ETC EACH REQUIRES MORE AND MORE ENERGY!!!!!!!!! ITS HARDER TO REMOVE SUBSEQUENT ELECTRONS BECAUSE EACH TIME ONE IS REMOVED, THE NUCLEUS PULLS ON REMAINING ELECTRONS MORE STRONGLY. IT’S REALLY HARD to remove an electron from a stable (full) shell.

Each atom is rated on a scale from 0-4 Metals have low electronegativity Nonmetals have high electronegativities FLUORINE HAS THE HIGHEST!!!