Transcript Chapter 14 Trends in the Periodic Table

Chapter 14
Chemical Periodicity
People who came up with trends:
1.J.W. Dobereiner (1780-1849)
stated there were triads
Li, Na, K
Ca, Sr, Ba
Cl2, Br2, I2
3 elements with similar
properties
atomic mass of the middle
element was about average of
the other two
2.Cannizzaro (1826-1910)
atomic masses were added to the
periodic table
3. J.A.R. Newlands (1837-1898)
62 known elements
found every 8th element had similar
properties
“Law of Octaves”
4.Dmitri Mendeleev (1834-1895)
Lothar Meyer (1830-1895)
1st periodic table based on atomic
masses
left gaps where undiscovered
elements would later go
Periodic Law – The chemical and
physical properties of the
elements
are periodic functions of
their
atomic number
some elements are out of order if
listed according to atomic mass
Te and I
Ar and K
Co and Ni
5.Mosely (1887-1915)
working with x-rays he determined
the atomic numbers of the
elements
periodic table based on atomic
number
Quick review of the periodic
table
 Trends
1. Atomic radius
Monatomic atoms – distance
from
the nucleus to the
outermost
electron of an atom
Diatomic – ½ the distance from
one adjacent atom to another
Group or family
Atomic number is directly
proportional to the atomic
radius
Li
2s1
Cs
6s1
Series or period
atomic number is a indirect
proportion to the atomic radius
ex. Which has a larger atomic
radius?
Li
2s1
3 p+
nuclear attraction
in close)
or
Ne
2p6
10p+
More protons has a
stronger
(pulls
Out of the following pairs state
which has a larger atomic radius.
S or Po
Mg or Cl
Li or Rn
If not in the same row or column, it may
not be possible to tell which is larger.
So, pick an element that is in the same row
or column as BOTH elements.
Li
Ne
Rn
So, Li > Ne
Ne < Rn
than
Can’t say which is
larger
Can say both Li, Rn are larger
Ne
Which is larger Cs or Ne?
Put in order from largest to smallest
radius.
Summary
Start with the last electron configuration
Look for same configuration, more energy
means it is larger
Look for same last energy level, more
protons makes it smaller
Look for adjoining element
2. Ionization Energy (IE)
Energy needed to remove the
outermost electron from an atom
in its gaseous state
Unit kJ/mole
Group or family
Atomic number is indirectly
proportional to the IE
Increasing atomic number leads
to a lower IE
Which would have a higher IE?
Li
Li
2s1
(high IE)
to
Cs
Cs
6s1
(low IE)
electrons further
away, so it’s easier
remove
Series or Periods
Atomic number is directly
proportional to the IE
Increasing atomic number equals
higher IE
Which would be higher Li or Ne?
Li
2s1
Ne
2p6
(same energy level)
3 protons
higher
10 protons (stronger
nuclear attraction)
Which is higher?
Mg or P
Na or Cl
Rank in terms of IE high to low
Sr, C, F
Which has higher IE, N or O?
**** ONLY TAKE BALANCE INTO CONSIDERATION
WHEN DEALING WITH ADJACENT ELEMENTS.
Summary
Look at:
1. How close to the nucleus
2. How many protons
3. Balance adjacent elements
Rank from low to high
Ca Sr As
Se
3. Second ionization energy, IE2
The energy needed to remove the
second outermost electron
AFTER
the outermost has already
been
removed.
Na + IE1  Na+ + e11p
11p
11e
10e
Na+ + IE2 
What will this produce?
Na+ + IE2  Na+2 + e11p
10e
11p
9e
4. Third ionization energy
Energy needed to remove the third
outermost electron after the two
outermost electrons have been
removed.
Na+2 + IE3  Na+3 + e11p
11p
9e
8e
IE3 is always applied to a (+2) ion.
IE2 is always applied to a (+1) ion.
How would you rank IE, IE2, IE3?
(high to low)
IE3 > IE2 > IE
Examples:
Which of the following elements would have the
higher IE2?
Be, C or F
*Remember IE2 is applied to something that has already
lost one electron.
Be+
2s1
4p+
lowest
2p1
6p+
C+
F+
2p4
9p+
highest
Which of these would have the highest IE3 ?
Be,
C, F
Remember that IE3 is applied to (+2 ion).
Be+2
C+2
F+2
1s2
2s2
2p3
6 p+
Highest
lowest
(closest to nucleus)
9p+
Rank the following elements in terms of IE2
from low to high.
O, S, F
O+
2p3
S+
3p3
F+
2p4
4. Chemical activity
An elements ability to replace another
element in a chemical compound
Li + H20 
Na + H20 
K + H2O 
Which was more active?
K
5. Metals
Group or family – activity increases
with increasing atomic
number
Series or Period – activity decreases
with increasing atomic number
Rank activity from low to high
Be, Ca, Ba
low
high
6.Nonmetals
Group or family- activity decreases
down the group
Series or period- activity increases
as atomic number increases
Rank from low to high
Se, S,Cl
What is the most active metal?
Fr
What is the most active nonmetal?
F
6. Ionic radius
the distance from the nucleus to
the outermost electron of a
naturally occurring ion
Want to achieve electron config of a Noble Gas
Examples:
Oxygen : 1s2 2s2 2p4
Gains 2 eatom of O  O -2-
Which would have a larger ionic
radius?
Sr, Mg, Al
First decide which ion is formed
Sr 2+ , Mg 2+ , Al 3+
Check electron configuration
4p6
largest
2p6
2p6
check protons
12 p+
13 p+
smallest
So Al, Mg, Sr
Rank in terms of ionic radius: large to small:
N,
S, F, Br
N3-,
S2-, F1-, Br1-
2p6
3p6 2p6 4p6
7p+
9p+
largest
Cations are SMALLER than the atom
from which they naturally come.
Anions are LARGER than the atom
from which they naturally come.
Cations are positive.
Anion are negative charge.
7.Electron Affinity
The energy absorbed or released
when an atom gains an
electron
X + electron + EA  X-
Higher energy less stable or balance
Lower energy more stable or balance
Which will have the highest EA
B
N
F
Before
2p1 __ __ __
2p3 __ __ __
2p5 __ __ __
After
2p2 __ __ __
2p4 __ __ __
2p6 __ __ __
Noble gas configuration will be the
lowest
Equations using EA
Show Na gaining an electron
Na + e- + EA  Na3s1 __
exothermic
-53 kJ
3s2 __ more balance negative
energy
Show Mg gaining an electron
Mg + e- + EA  Mg- endothermic
3s2 __
+19 kJ
3p1 __ __ _
becomes less balanced, positive
energy
Mg has a higher EA than Na
Element
IE
EA
(kJ/mol)
(kJ/mol)
Na
496
-53
As
944
-77
Mg
738
19
A. Write a chemical equation showing Mg losing one
electron.
B. Tell whether the reaction is exothermic or endothermic.
HOMEWORK
Write a chemical equation showing arsenic gaining an
electron.
Is this reaction endothermic or exothermic?