Download Periodic Properties of the Elements

Periodic Properties of the
Elements
Paramagnetic vs. Diamagnetic
Paramagnetic elements
Diamagnetic Elements
 Have unpaired electrons
 Attracted to a magnetic field
 Some can even become
charged by a magnetic field
 Have no unpaired electrons
 Are weakly repelled by a
magnetic field
Examples: copper, neon, mercury
Examples: iron, sodium, oxygen
Effective Nuclear Charge
 Coulomb’s law: the magnitude of the electric force
between two charged particles is given as
F = kQ1Q2
d
2
Q = magnitude of charge on a particle
d = the distance between their nuclei
k = constant
Conclusion: As the distance
between the nucleus and an
electron increases,
their attractive force decreases
Effective Nuclear Charge
 We can estimate the net attraction between each
electron and the nucleus
 Electrons repel each other BUT
 They are attracted to the protons in the nucleus
 Always smaller than the actual nuclear charge due to
ELECTRON SHIELDING
 Zeff increases as we move across a period
 Why?
Shielding of inner electrons stays constant
Nucleus increases + charge
Effective Nuclear Charge
 Increases as we move across a period
WHY?
A proton is added to the nucleus as atomic number increases
No new electrons are added to the core – shielding remains constant
 Changes far less down a group
WHY?
The distance between the nucleus and valence electrons increases
significantly
Atomic Radius
 Measured by the
distance between two
nuclei of nonbonding
atoms or bonding atoms
General trends for Atomic Radius
 Down a group: INCREASES
WHY?
As n increases, the outer electrons have a greater
probability of being further from the nucleus
 Across a period: DECREASES
WHY?
Zeff increases as we move across the period
Electrons are drawn closer to the nucleus
General Trends for Ionic Radii
 Cations: SMALLER than
parent atoms
WHY?
The most spatially extended orbital is vacated
Amount of e- repulsions decreases
 Anions: LARGER than
parent atoms
WHY? More electron/electron repulsions occur
Electrons spread out
General Trends for Ionization Energy
The amount of energy required to remove an electron from the gas phase
Of an atom or ion (in Joules)
 Down a group: DECREASES
WHY?
- With each added energy level, valence electrons are further from the nucleus
- Less energy is needed to overcome the weaker force between the
nucleus and the valence electrons
 Across a period: INCREASES
WHY?
- Zeff increases, pulling outer electrons closer to the nucleus
- More energy is required to overcome that force
Electron removal in atoms
 Electrons in higher
energy levels leave first
 These experience the
least effective nuclear
charge, and require the
least amount of energy
to remove
 s electrons leave before
d electrons
WHY?
Electrons in a higher principle energy level
have a greater probability of being
further from the nucleus
4s
3d
Electron configurations in ions
 Write the configuration
for vanadium ion, V+3
 Write the configuration
for the Se2- ion.
Exceptions to trends: Ionization
Energy
 Which has higher
ionization energy: Mg or
Al?
Another exception example:
 Which has lower
ionization energy: P or
S?
General exceptions to ionization
energy trend
 Group 2 to Group 13  DECREASE (expect increase!)
 WHY?In Group 13, the electron is removed from a p orbital, which is
farther from the nucleus
In Group 2, the electron is removed from an s orbital, which is closer
To the nucleus
 Group 15 to Group 16  DECREASE (expect increase!)
 WHY?
- In Group 16, the electron is easier to remove because one of the p orbitals has
two electrons, giving more electron repulsions and increasing the distance
between the nucleus and the outer electrons
- In Group 15, the electron harder to remove, because the electrons are closer to
the nucleus
Electron Affinity
 The attraction of the atom for an added electron
 Measured in Joules
 The ease with which an atom GAINS an electron
General trends in Electron Affinity
 Down a group: becomes more POSITIVE (endothermic)
WHY?
Outer energy level is farther away from nucleus
Nucleus is less attracted to outer electrons
 Across a period: becomes more NEGATIVE (exothermic)
WHY?
Zeff increases
Nucleus is more attracted to outer electrons
Exceptions to trend: Electron affinity
 Noble gases: Have positive electron affinities
 WHY?
 Adding an electron requires a new principal energy level
 All other electrons are in the core and greatly shield the
nucleus from the valence electrons
 Other exceptions?
 Group 2 is more positive than Group 1
 Group 15 is more positive than the Group 14