Transcript SURVEY OF ELEMENTS

SURVEY OF ELEMENTS
• Atoms of most elem are hard to find.
Electron configuration
1s1
1s2
(stable)
1s22s1
1s22s2
1s22s22p 1
1s22s22p 2
...
1s22s22p 6
(stable)
1s22s22p 63s1
1s22s22p 63s2
1s22s22p 63s23p 1
...
1s22s22p 63s23p 6
(stable)
...
1s22s22p 63s23p 63d 10 4s246
(stable)
• Why? Valence (outer) shell usually not filled completely.
They react to form chem bonds to gain an octet!!!
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into groups with similar properties
 Know properties of elem based on e- config
Periodic Table
 Elements above and below each other have
similar e- config and therefore similar properties
Several properties show a periodic change across
or down the table = trends
e- Config and the Periodic Table
Discoveries
• Newlands Octaves early 1800's
– Placed elements in order by mass
• Many elements were unknown
– Every 8th element has similar properties
• F and Cl
• Li, Na, K
• Mendeleev
– Ordered elements in table by mass, placing elem with similar
properties above one another. He left gaps assuming some
elements were unknown
– Predicted properties of missing elements
• Moseley
– Determined # of + charges in the nucleus
– Order of elements on periodic table is now by increasing
atomic number
Structure of Per Table
• Periods = rows (1 -7)
• Groups or families = columns
– 1 - 18
– Know
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Alkali metals = grp 1 (very active metals)
Alkaline earth metals = grp 2 (active metals)
Halogens = grp 17 (very active nonmetals)
Noble or inert gases = grp 18 (inactive gases)
– Relate character of each group to it's econfiguration
Regions of Per Table
• Blocks
– s, p, d, f
• Main table elem = s and p blocks
• Transition elem = d block
• Rare earth elem = f block
– Lanthanides and actinides
• Metals, nonmetals, metalloids
– Know general characteristics of each
• e- sea model of metals
Periodic Trends
• Atomic radius - Size of the atom
– Effects of shielding of valence e-s by kernel e-s
• Ionization energy - meas of ability to lose an e– energy change when a valence e- is emitted from an atom
– High for nonmetals low for metals
• e- affinity - meas of ability to gain an e– Energy change associated with the acceptance of an e- into the
valence shell
• Usually (+) for metals and (-) for nonmetals electronegativity
• Electronegativity - meas of ability of atom to attract e-s in a
covalent bond
– High for nonmetals, low for metals
Periodic Trends
• Atomic radius
• Ionization energy
• Electronegativity
Section Review
Mn: [Ar]4s2 3d?
How many 3d electrons does Mn have?
4, 5, 6
Periodic Trends
Trends in thePeriodic Table
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Atomic radius
Ionic radius
Ionization energy
Electron affinity
Metallic character
Atomic Radius
• Hard to measure
• decrease left to right across a period
Zeff = Z - S
where
Zeff => effective nuclear charge
Z => nuclear charge, atomic number
S => shielding effect
Shielding Effect
Coulombic (electrostatic) forces are affected by
distance betwee the charges and size of the charges
Na
11+
2e-
8e-
1e-
Al
13+
2e-
8e-
3e-
Cl
17+
2e-
8e-
7e-
The inner (kernel) e-s shield the
valence shell e-s from the
protons in the nucleus
Sodium’s valence e-s see only 1
proton ([11+] – [10-]).
Aluminum’s valence e-s see 3+
charges from the nucleus ([13+]
– [10-]). How many positive
charges from the nucleus do the
valence e-s in Cl see?
Atomic Radius
• increase top to bottom down a group
– each additional electron “shell” increases the
diameter of the atom
• increases from upper right corner to the
lower left corner
– across a period as shielding is constant while
charges in nucleus and valence shell increase
Atomic Radii
Ionic Radius
• same trends as for atomic radius
• positive ions smaller than atom
• negative ions larger than atom
Ions are isoelectric with a noble gas atom
Al
Na
11+
2e-
8e-
O
1e-
13+
2e-
8e-
Ne
8+
2e-
6e-
10+
2e-
8e-
3e-
Ions are isoelectric with a noble gas atom
Al3+
Na1+
11+
2e-
8e-
O2-
8+
13+
2e-
8e-
Ne
2e-
8e-
10+
2e-
8e-
Atomic radius vs Ion radius
Ionic Radii
Ionic Radius
Isoelectronic Series
• series of negative ions, noble gas atom, and
positive ions with the same electronic
configuration
• size decreases as “positive charge” of the
nucleus increases
e- Configuration of Elements
Octet Rule
• Atoms of elements gain, lose, or share
electrons in order to obtain an octet (full
outer e- level)
– Eight e-s for all atoms except H and He
– Extra stability – lower energy
– Metals want to lose, and nonmetals gain e-s
M + energy  M+ + e- (endo)
NM + e-  NM- + energy (exo)
Ionization Energy
• energy necessary to remove an electron to form
a positive ion
• low value for metals, e-s easily removed
• high value for non-metals, e-s difficult to
remove
• increases from lower left corner of periodic
table to the upper right corner
1st Ionization Energy
Ionization Energies
» Abnormalities caused by extra stability of full and half full sublevels
Ionization Energies
first ionization energy
• energy to remove first electron from an atom
second ionization energy
• energy to remove second electron from a +1
ion etc.
Successive Ionization Energies
Electron Affinity
• energy released when an electron is added to
an atom
• same trends as ionization energy, increases
from lower left corner to the upper right
corner
• metals have low “EA”
• nonmetals have high “EA”
M + e-  M- + energy
Electronegativity
• All atoms want an octet
– Nonmetals want to add e-s to complete their
outer level
• Nonmetals attract e-s strongly
• They have high electronegativities
– Metals want to lose their outer level e-s to obtain
an octet
• Metals do NOT attract e-s strongly
• They have low electronegativities
Electronegativity
• The atom’s attraction for the electrons in a
covalent bond