Transcript trends in the PT

Trends & the Periodic Table
Trends
• see properties change in predictable ways
based location of elements on PT
• some properties can be predicted:
density
melting point/boiling point
* atomic radius
* ionization energy
TABLE S
* electronegativity
* anyone know where we can find these values?
periodic properties: when graph see a repetitive pattern
(Note: graph doesn’t have to be a straight line)
you will use a
blank PT to
draw arrows
which show the
trends!
Going down column 1:
Period
Element
Configuration
1
H
1
2
Li
2-1
3
Na
2-8-1
4
K
2-8-8-1
5
Rb
2-8-18-8-1
6
Cs
2-8-18-18-8-1
7
Fr
2-8-18-32-18-8-1
the # energy levels increase as go down - makes sense that
atoms get larger in size
# principle
energy levels ↑
Atomic Radius
• atomic radius:
defined as ½ distance between neighboring
nuclei in molecule or crystal
• affected by:
1. # energy levels
2. proton pulling power (PPP)
size increases
TRENDS:
atoms get larger as go
down column:
↑# principal energy levels
atoms get smaller as move
across series:
↑ PPP
“proton pulling power”
Cs has more energy levels, so it’s bigger than Li
Li: group 1 period 2
Cs: group 1 period 6
increasing atomic radius
↑ # principle energy levels
atomic radius ↑ as go top to bottom of column,
because # energy levels ↑
As go across rows, elements gain electrons,
What is happening?
but they are getting smaller!
Family
IA or 1
IIA or 2
IIIA or 13
IVA or 14
VA or 15
VIA or 16
VIIA or 17
VIIIA or 18
Element
Li
Be
B
C
N
O
F
Ne
Configuration
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
↑ PPP
increasing number of energy levels
increasing atomic radius
decreasing atomic radius
Why does this happen..
• as go from left to right, you gain more
protons (atomic number increases)
• results in greater “proton pulling power”
– remember: nucleus is (+) and electrons are (-)
so e- get pulled towards the nucleus
• more protons you have, the stronger PPP
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as go across row size tends to decrease a bit
because of greater PPP “proton pulling power”
We can “measure” the PPP
by determining the
effective nuclear charge
• this is pull of protons actually felt by valence eto calculate effective nuclear charge:
nuclear charge
- # inner shell electrons (not including valance e-)
effective nuclear charge
+7
effective nuclear charge
+1
effective nuclear charge
calculate “effective nuclear charge”
(# protons minus # inner electrons)
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H and He:
only elements
whose valence
electrons feel
full nuclear
charge (pull)
NOTHING TO SHIELD THEM from protons!
increasing number of energy levels
increasing atomic radius
decreasing atomic radius
increased e- shielding
Look at all the shielding Francium's one val e- has!
• barely feels proton pull of nucleus
• Fr loses it’s val e- the easiest, making
Fr the most reactive metal!
Ionization Energy
• definition: amount energy required to
remove farthest valence e- from atom
• 1st ionization energy: energy required to
remove most loosely held valence electron
(valence e- farthest from nucleus)
– 2nd ionization energy: next most loosely held val e– 3rd ionization energy: next most loosely held val e-
Trends in Ionization Energy
• What do you think happens to the ionization
energy as go down column (top to bottom) of PT?
decreases
• As go across row (left to right) ?
increases
Electronegativity
• ability of atom to attract e- to itself so can
form bonds with other elements
•
noble gases don’t have electronegativity values
– tend not to form bonds (8 val e-)
• Fluorine (F): most electronegative element
= 4.0 Paulings
• Francium (Fr): least electronegative element
= 0.7 Paulings
increasing number of energy levels
increasing atomic radius
increasing electron shielding
decreasing atomic radius
F
Fr
increasing ionization energy
increasing electronegativity
due to  PPP
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elements in same group:
- val e- farthest from nucleus are easiest to remove
easier for Cs (bottom of column) to lose val e- than
Li (top of column) so Cs is a more reactive metal!
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elements in same row: easier to take away val e- if less protons
Li has less “proton pulling power” than Ne so easier to
remove Li’s valence electrons
Reactivity of Metals
• judge reactivity of metals by how easily
give up electrons to form (+) ions
– metals are losers!
• most reactive metals: Fr (then Cs)
• for metals:
reactivity ↑ as ionization energy ↓
Trends for Reactivity
(Metallic Character) of Metals
• increases as go down column (top to bottom)
–easier to lose electrons!
• decreases as go across row (left to right)
–more difficult to lose electrons!
Reactivity of Non-metals
• judge reactivity of non-metals by how
easily gain electrons
– non-metals are winners!
• F: most reactive non-metal
• for non-metals:
reactivity ↑ as electronegativity ↑
Trend for Reactivity of Non-metals:
• depends on PPP
– ↑ PPP means more reactive the non-metal
• increases as go across row (left to right)
• decreases as go down column (top to bottom)
– shielded by more inner-shell electrons
positive ions (cations)
• formed by loss of e• cations always smaller than parent
atom
1e2e-
Li
Ca
2e-
Li+1
negative ions or (anions)
• formed by gain of e-
• anions always larger than parent
atom
Allotropes
• different structural forms of element in
same phase
– different structures and properties
– examples: C and O
graphite and diamond: both carbon in solid form
oxygen & ozone:
both forms of oxygen in gas form
O2 (g)
• form oxygen necessary for life
O3 (g)
• form oxygen toxic to life