Transcript Do Now - dlib.info

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Do Now
• Name one element that has similar chemical
properties to calcium and why they are
chemically similar.
• Any element in the same group is chemically
similar because it would have the same number
of valence electrons.
Trends in the
Periodic Table
Influenced by three factors
1. Energy Level
• A higher energy level is further
away.
2. Charge on nucleus (# protons)
• More charge pulls electrons in
closer.
• 3. Shielding effect (a blocking effect?)
#1. Atomic Size - Group trends
• As we go down a
group:
• each atom has
another energy
level,
• so the atoms get
bigger.
H
Li
Na
K
Rb
#1. Atomic Size - Period Trends
• Going from left to right across a period, the size
gets smaller.
• Electrons are in the same energy level.
• But, there is more nuclear charge.
• Outermost electrons are pulled closer.
Na
Mg
Al
Si
P
S Cl Ar
Rb
K
Atomic Radius (pm)
Period 2
Na
Li
Kr
Ar
Ne
H
3
10
Atomic Number
Atomic size increases in these
directions:
#2. Trends in Ionization Energy
• Ionization energy is the amount of
energy required to completely remove
an electron to form an ion.
• Removing one electron makes a 1+
ion.
• The energy required to remove only
the first electron is called the first
ionization energy.
Ionization Energy
• The second ionization energy is the
energy required to remove the second
electron.
• Always greater than first IE.
• The third IE is the energy required to
remove a third electron.
• Greater than 1st or 2nd IE.
Symbol First
H
He
Li
Be
B
C
N
O
F
Ne
1312
2731
520
900
800
1086
1402
1314
1681
2080
Second
Third
5247
7297
1757
2430
2352
2857
3391
3375
3963
11810
14840
3569
4619
4577
5301
6045
6276
What factors determine IE
• The greater the nuclear charge, the
greater IE.
• Greater distance from nucleus
decreases IE
Shielding
• The electron on the
outermost energy level
has to look through all
the other energy levels to
see the nucleus.
• Second electron has
same shielding, if it is in
the same period
Ionization Energy - Group trends
• As you go down a group, the
first IE decreases because...
• The electron is further away
from the attraction of the
nucleus
• There is more shielding.
Ionization Energy - Period trends
• All the atoms in the same period have
the same energy level.
• Same shielding.
• But, increasing nuclear charge
• So IE generally increases from left to
right.
First Ionization energy
He
H
• He has a greater IE than
H.
• Both elements have the
same shielding since
electrons are only in the
first level
• But He has a greater
nuclear charge
Atomic number
First Ionization energy
He
l
l
H
l
l
Li
Li has lower IE
than H
more shielding
further away
These outweigh
the greater
nuclear charge
Atomic number
Ne
First Ionization energy
He
N F
H
C O
Be
B
Li
Na
Atomic number
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Do Now
• Which atom is larger and why:
• Ca or Ba
• Which atom has a higher ionization energy
and why:
• Na or Fr
#3. Trends in Electronegativity
• Electronegativity is the tendency for an
atom to attract electrons to itself when it
is chemically combined with another
element.
• They share the electron, sometimes it’s
not equal sharing.
• An element with a large electronegativity
pulls electrons toward itself strongly!
Electronegativity Group Trend
• Down a group
• Electrons are farther from the
nucleus
• More electrons cause shielding,
• Atoms are more willing to share
electrons.
• Low electronegativity.
Electronegativity Period Trend
• Metals
• On the left of the table.
• They let their electrons go easily
• low electronegativity
• Nonmetals
• At the right end of the PT
• They want more electrons.
• They try to take them away from others
• High electronegativity.
The arrows indicate the trend:
Ionization energy and Electronegativity
INCREASE in these directions