Transcript Atomic Radius

Periodic Trends
 Suggested Reading
Pages 150 - 164
I
II
III
 Section 5-3
Valence Electrons
 Electrons available to be lost,
gained, or shared in the
formation of chemical
compounds
Outer energy level
Atomic Radius
 Distance from the center of atom’s
nucleus to outermost electron.
Atomic Radius
Decreases UP and to the RIGHT
Or Increases DOWN and to the LEFT
1
2
3
4
5
6
7
Atomic Radius
Atomic Radius (pm)
250
K
Na
200
Li
150
100
Ar
Ne
50
0
0
5
10
Atomic Number
15
20
Atomic Radius
Describe in terms of atomic structure:

Going down a group from top to bottom,
adding energy levels.

Higher energy levels have larger orbital's
Describe in terms of atomic forces:
 Shielding Effect ~ inner core e- block the
attraction between the nucleus and the
valence e-
Atomic Radius
Describe in terms of atomic structure:
 Electrons remain in the same energy level (not
farther away)
Describe in terms of atomic forces:
 Increased nuclear charge (+) without additional
shielding pulls e- in tighter
Ion
 An atom or group of bonded
atoms that has a positive or
negative charge.
Ionic Radius
Cations (+)
lose
e-
smaller
Anions (–)
gain
e-
larger
© 2002 Prentice-Hall, Inc.
Ionic Radius
 Larger – down a group.
 Smaller – across a period.
 Cations: Smaller
than neutral atom
 Anions: Larger than
neutral atom
6.3
Trends in Ionic Size
Size generally increases
Trends
in Ionic Size
Ionization Energy
 The amount of energy required to
remove an electron from a neutral atom.
 Increases UP and to the RIGHT
1
2
3
4
5
6
7
Ionization Energy
Ionization Energy
 Opposite trend from atomic radius.
 Larger atoms ~electrons held less
strongly ~ takes less energy to remove
one.
 Smaller atoms ~ electrons held more
strongly ~ takes more energy to remove
one.
Ionization Energy
 Why small jumps within each group?
 Stable
electron
configurations
do not easily
give up
electrons
1st Ionization Energy (kJ)
2500
2000
1500
1000
500
0
0
5
10
Atomic Number
15
20
*1st, 2nd, and 3rd Ionization Energies
 Amount of energy to remove
1st electron, 2nd electron, 3rd
electron.
 Each higher ionization
requires more energy.
Na  Na+ + e-
496 KJ/mol
Na+  Na+2 + e- 4565 KJ/mol
Na+2  Na+3 + e- 6912 KJ/mol
Electron Affinity
The energy change that occurs
when an electron is added to an
atom.
Negative Electron Affinities
Energy is given off when an
electron is added to an atom.
 Non-Metals tend to gain
electrons.
 Non-Metals have NEGATIVE
affinities.
Positive Electron Affinities
 Energy is required to add an
electron to an atom.
 Metals tend to lose electrons
 Metals have POSITIVE affinities.
Noble Gas Electron Affinities
 Noble Gases have high positive
electron affinities.
 Octet Rule!
8 valence electrons
Electronegativity
 The ability of an atom to
attract electrons
 Predict using octet rule and
atomic radius.
 F is most electronegative, Cs
and Fr are least
electronegative.
Electronegativity