Download Trends of the Periodic Table - Laureate International College

Trends of the Periodic Table
Background
• Electrons can jump between
shells (Bohr’s model supported
by line spectra)
•The electrons can be pushed so
far that they escape the attraction
of the nucleus
Losing an electron is called
ionization
Ions
• An electrically charged particle formed when
an atom or molecule loses or gains an
electron.
• Q: what would the charge be on an atom that
lost an electron?
A: +1 (because your losing a -ve electron)
called a cation
• Q:Gained two electrons?
• A: -2 (because you gain 2 -ve electrons) called
an anion
Ionization energy
• Ionization energy is the energy required to remove
one outer electron from an atom.
Most weakly held
11p+
12n°
Na
+
+
Ionization
Energy
E ionization
+1
11p+
12n°
Na+1 (g)
+
+
1e-
1e-
Predict…
Is there an IE trend in the PT of E?
• Down a group?
I.E. DECREASES because:
o More energy levels, resulting in a decrease in attractive
forces between the nucleus and valence electrons.
Removing one electron becomes easier.
• Across a period?
I.E. INCREASES because:
o Electrons are added along the same energy level,
increasing the attractive forces between protons and
valence electrons requiring more IE to remove them.
Ionization energy vs. atomic number
Electrostatic Force Theory
(EFT)
• The degree of attraction or repulsion experienced by
two charged particles depends on TWO main factors:
1. The distance between them
2. The magnitude of the charge.
• As the # of protons in the nucleus increases, the
electrons will experience a greater electrostatic
attraction for the nucleus.
• As electrons are positioned in energy shells further
from the nucleus, they will experience less
electrostatic attraction from the positive nucleus.
What does this mean?
Look at the arrangement of electrons
Is being ‘pulled’ in by the 11 protons
11p+
12n°
BUT is ‘shielded’ by 10 electrons in
front of it
Chlorine
Sodium
Is being ‘pulled’ in by the 17 protons
BUT is ‘shielded’ by 10 electrons in
front of it
17p+
18n°
More protons means greater attraction between nucleus
and outer electron thus higher ionization energy.
Electron Affinity
• The energy released when a free electron is added to the
lowest available energy shell of an atom in the gas phase.
-1
17p+
18n°
Cl
+
+
1e-
1e-
17p+
18n°
Cl-1 (g)
Electron
+ Affinity
+
E.A.
Predict…
Is there an EA trend in the PT of E?
• Down a group?
EA. DECREASES because:
o More energy levels are added increasing the
distance between the nucleus and valence
electrons.
• Across a period?
EA. INCREASES because:
o More energy is released as atoms become more
stable. For example, elements in group 7 are very
stable with the addition of 1 e-, thus a higher EA.
Elements in group 1 become less stable with the
addition of 1 e-, thus a lower EA.
Atomic Radius
• the estimated distance from the centre
of the nucleus to the outer edge of the
atom.
• Typically radii = 100 pm (picometer)
» 1 pm = 1 x 10-12 m
Predict…
Is there a trend in Atomic Radii in the PT of E?
Down a group?
• Atomic size INCREASES because:
o Energy levels are added, therefore electrons are at a
greater distance from the nucleus.
o There is an increase in shielding effect due to the
inner electrons.
Across a period?
• Atomic size DECREASES because:
o Electrons are added along the same energy
level, so are protons, therefore overall
attraction increases, atomic radius
decreases.
Atomic radius vs. atomic number
Classwork/Homework
• Trends Worksheet
• Follow directions on the sheet and answer
the questions.
• Hint: Ignore Hydrogen when looking at
trends.
• Look at many periods/groups when
summarizing trends.