• 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).
•
•
•
•
1ST IONIZATION ENERGY= ENERGY TO REMOVE 1 ELECTRON
2ND IONIZATION ENERGY = ENERGY TO REMOVE 2ND
3RD IONIZATION ENERGY= 3RD…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.
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•
•
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Each atom is rated on a scale from 0-4
Metals have low electronegativity
Nonmetals have high electronegativities
FLUORINE HAS THE HIGHEST!!!