Transcript Unit 4 Periodicity

Chemistry
Unit 4: The Periodic Table
and Periodic Trends
(Periodicity)
Background on the Periodic Table
Dmitri Mendeleev: given credit
for Periodic Table (~1870)
-- organized Table by
increasing atomic mass
-- left spaces and predicted
properties of undiscovered
elements
•
put elements in
order of increasing
atomic number
______________.
Mendeleev
Regions of the Table
metals: left side of Table(1-3 valence e-); form
cations
properties:
•lustrous
(shiny)
•ductile
(can pull
into wire)
•good conductors
(heat and electricity)
•hard
•malleable
(can hammer
into shape)
Regions of the Table (cont.)
nonmetals: right side of Table(5-7 valence e; form anions by gaining electrons
properties: good insulators, poor conductors
gases or brittle solids
dull
neon
sulfur
iodine
bromine
Ne
S8
I2
Br2
Regions of the Table (cont.)
metalloids (semimetals): “stair” between metals
and nonmetals (B, Si, Ge, As, Sb, Te, At)
metals
computer chips
properties: (intermediate)in-between those of metals
and nonmetals; “semiconductors”
Si and Ge
computer chips
Periodicity
there are trends in properties of elements
-- left-right AND up-down trends
atomic radius: the size of a neutral atom
…increases as we go
WHY? add a new energy
level each time
…decreases as we go
WHY? it has to do with…
Increase in nuclear charge
Atomic Radii
IA
IIA
IIIA
IVA
VA
VIA
VIIA
Li
Be
B
C
N
O
F
1.52
1.11
0.88
0.77
0.70
0.66
0.64
Na
Mg
Al
Si
P
S
Cl
1.86
1.60
1.43
1.17
1.10
1.04
0.99
K
Ca
Ga
Ge
As
Se
Br
2.31
1.97
1.22
1.22
1.21
1.17
1.14
Rb
Sr
In
Sn
Sb
Te
I
2.44
2.15
1.62
1.40
1.41
1.37
1.33
Cs
Ba
Tl
Pb
Bi
2.62
2.17
1.71
1.75
1.46
= 1 Angstrom
ionic radius: the size of an ion
cations
Ca atom
anions
Ca2+ ion
Cl atom
Cl1– ion
20 p+
20 p+
17 p+
17 p+
20 e–
18 e–
17 e–
18 e–
Cl
Cl1–
Ca
Ca2+
cations lose electronssmaller
Anions gain electrons
larger
IA
Atomic
Radii
Li
1.52
Na
1.86
K
2.31
Rb
2.44
Cs
Ionic
Radii
IIIA
IVA
Be
B
C
0.88
0.77
Al
Si
1.60
1.43
1.17
Ca
1.97
Ga
Ge
1.22
Sr
1.11
Mg
VA
VIA
VIIA
N
O
F
0.70
P
0.66
S
0.64
Cl
1.10
1.04
0.99
As
Se
Br
1.22
1.21
1.17
1.14
In
Sn
Sb
Te
2.15
1.62
1.40
1.41
I
1.33
Ba
Tl
Pb
Bi
1.71
1.75
1.46
2.62
2.17
Li1+
Be2+
0.60
Na1+
0.31
0.95
0.65
K1+
Cations: smaller
than parent atoms
IIA
Mg2+
Ca2+
N31.71
Al3+
0.50
Ga3+
1.33
Rb1+
0.99
Sr2+
0.62
1.48
Cs1+
1.13
Ba2+
0.81
Tl3+
1.69
1.35
0.95
In3+
1.37
O21.40
F11.36
S21.84
Cl11.81
Se2-
Br1-
1.98
1.85
Te2-
I1-
2.21
2.16
= 1 Angstrom
Anions: LARGER
than parent atoms
ionization energy: the energy required to remove
an e– from an atom
Each successive ionization requires
more energy than the previous one.
As we go , 1st I.E…. decreases.
(due to the shielding effectincrease in the number of
energy levels)
As we go
, 1st I.E…. increases.
•Nonmetals tend to gain therefore having
a high first ionization energy.
•Metals tend to lose-low first ionization
energy
electronegativity: the tendency for
a bonded atom to
attract e– to itself
As we go , electronegativity… decreases.
As we go
, electronegativity… increases.
•Nonmetals tend to gain therefore having a high
electronegativity.
•Metals tend to lose-low electronegativity
Reactivity of Metals
• Increases down a column
– Reasons: Size (value of n), low ionization energy,
and the shielding effect
• Decreases left to right across a period
– Reasons: Stronger nuclear charge and Increase in
ionization energy
Reactivity of Nonmetals
• Increases left to right across a period
– Why?
• Smaller in size
• Stronger nuclear charge
• Increased ionization energy
• Decreases down a column
– Why?
• Decreased electronegativity
• Larger in size
Reactivity Overview
• Fr-most reactive metal
• F-most reactive nonmetal
• Exception: Elements with halffilled sublevels are more stable
than those with empty orbitals