Transcript Lecture 4.07 - Radii of the Elements (12)

Radii of the Elements
Radii of the Elements
• The atomic radius is defined as half the distance between
two adjacent atoms in a solid crystal.
• In a period, the atomic radius of each successive atom is
usually smaller than its preceding neighbor.
Li
Be
B
C
N
O
F
Ne
• In a group, the atomic radius of each successive atom is
larger than its preceding neighbor.
Be
Mg
Ca
Sr
Radii of the Elements
• The atomic radii decrease across a period because each
successive atom has one additional proton in the nucleus
and one additional electron in the valence (or in the case
of the transition elements, the next to last valence).
e-
e-
e-
e- 3p e
e- 4p e
eLi
Be
ee- 5p e
eB
e-
e-
e- 6p e
e-
eC
• The extra proton and electron increase the force of
attraction between the nucleus and the valence shell
pulling the valence electrons closer to the nucleus.
Thus the radii become smaller !
Radii of the Elements
• The atomic radii increase down a group because each
successive atom has one additional shell (PEL) around
its the nucleus.
ee-
ee3p
11p
Li
Na
19p
19p
K
Rb
• The extra shell increases the distance between the
valence electrons and the nucleus decreasing the force
of attraction between the nucleus and the valence
electrons.
Thus the radii become larger!
Radii of the Elements
Ex(1) As the atomic numbers of the elements in a period
on the Periodic Table increases, the volume of the
elements
(1) increases and both the electronegativity and
ionization energy increases.
(2) decreases and both the electronegativity and
ionization energy increases.
(3) increases and both the electronegativity and
ionization energy decreases.
(4) decreases and both the electronegativity and
ionization energy decreases.
(5) increases and the electronegativity decreases
while the ionization energy increases.
Radii of the Elements
Ex(2) In each of the following pairs of atoms, circle which
atom is the larger.
Pair #1: He or
Ne
Pair #3: Cl
or
Ar
Pair #2: Ca or
Mg
Pair #4: Sn or
Pb
Ex(3) Draw a full Bohr model (use full circles) for a neutral
atom of hydrogen in the ground state, neutral atom
of helium in the ground state, and a neutral atom of
lithium in the ground.
e
e- 1p
H
e- 2p e-
e- 3p e
He
Li
Radii of the Elements
Ex(4) In terms of atomic structure, explain why the radius of
helium is smaller than the atomic structure of hydrogen.
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Ex(5) In terms of atomic structure, explain why the radius of
lithium is larger than the atomic structure of hydrogen.
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Radii of the Elements
Ex(6) Which grouping of circles, when considered from
top to bottom, best represent the relative size of
the atoms of Li, Na, K, and Rb, respectively?
(1)
(2)
(3)
(4)