Transcript PERIODIC TRENDS OF THE ELEMENTS

PERIODIC TRENDS OF THE ELEMENTS
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Chemical properties
Physical properties
Atomic radii
Ionic radii
Ionization energy
Electron affinity
Electronegativity
Metallic & nonmetallic character
PERIODIC
TABLE ?
I INVENTED
IT !
Mendeleev
DEFINITIONS OF PERIODIC PROPERTIES
• Chemical properties refers to the tendency of atoms to
combine with other elements and / or molecules to form
compounds.
• Physical properties refers to characteristics such as density,
physical state (solid, liquid or gas), electrical and thermal
conductivity, malleability (can be hammered into shape),
ductility (can be stretched), color, luster (shininess),
brittleness, etc.
Definitions of periodic properties (cont’d)
• Atomic radii is measured as one half of the distance
between the nuclei of two adjacent similar atoms
(it measures atomic size)
• Ionic radii is measured as one half of the distance
between the nuclei of two adjacent similar ions
(it measures ion size)
• Ionization energy measures the energy needed to
remove an electron from a free atom in the gas state (it
measures how tightly electrons are bound to an atom)
• Electron affinity measures the energy released when
an electron is added to a free atom in the gas state ( it
measures how well atoms attract electrons)
Definitions of periodic properties (cont’d)
• Electronegativity measures the electron attracting
ability of an atom when it is bonded to another atom
• Metallic character measures the tendency of an
element to act as a metal in things such as
conductivity, tendency to lose electrons, shininess,
maebility and ductility
• Nonmetallic character measures the tendency of an
element to act as a nonmetal in things such
nonconductivity, tendency to gain electrons, low
luster and brittleness.
General organization of the periodic table
• Columns (families or groups) contain
elements with similar valence electron
configurations: ns1, ns2, ns2 np3, etc. and
therefore similar chemical properties
• Rows (periods or series) contain elements
with valence electrons at the same energy
level (n=1, n=2, n=3, etc.)
• Blocks of elements contain atoms with the
same valence electron orbital type (s, p, d or
f)
Orbital Blocks on the Periodic Table
metals
s
B
L
O
C
K
non metals
d BLOCK
p BLOCK
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N
E
R
T
G
A
S
f BLOCK
METALLOIDS
Common Chemical Families & Their Properties
Column I (Alkali Metals) Li Na K Rb Cs and Fr
• Form +1 cations
• Are highly metallic
• Reaction readily and rapidly with water to form hydroxides and
hydrogen gas
• React with the halogens to form ionic salts with the formula type MX.
For example: NaCl or KBr.
• Valence Electrons are ns1
Column II (Alkaline Earth Metals) Be Mg Ca Ba Sr and Ra
• Form +2 cations
• Are highly metallic
• Reaction readily and rapidly with water to form hydroxides and
hydrogen gas
• React with the halogens to form salts with formula type MX2 (for
example MgBr2 or BaCl2)
• Valence Electrons are ns2
Common Chemical Familes & Their Properties
page 2
Column VII (Halogens) F2 Cl2 Br2 I2 and At2
• All are diatomic elements (occur as a
molecule consisting of two atoms
• Are highly nonmetallic
• React ready and rapidly with metals to form salts
• Occur in all three phases at room temperature F2
and Cl2 are gases, Br2 is a liquid and I2 is a solid.
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Valence Electrons are ns2 np5
Common Chemical Families & Their Properties
page 3
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Column VIII (Noble Gases or inert gases)
All are unreactive under ordinary conditions
All have completed outer energy levels
All are gases at room temperature and pressure
• Their electron configuration is ( ns2 np6 ) This is a filled
outer shell, which the other atoms attempt to achieve through
chemical reactions and bonding.
Alkali metals
CHEMICAL FAMILIES
Alkaline Earth Metals
C
O
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M
U
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C
O
L
M
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N
I
II
Halogens
I
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R
T
Transitional
Metals
LANTHANIDE SERIES
ACTINIDE SERIES
C
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G
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V
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What factors determine the periodic
trends of the elements ?
1. The number of protons and electrons an atom contains.
(more protons create a greater nuclear charge which
attracts electrons more strongly)
2. Distance separating the outer electrons (valence
electrons) and the nucleus. (when electrons are closer
to the nucleus they are held more tightly)
3. Pairing of electrons in the outer energy level orbitals.
(paired electrons are more stable than unpaired
electrons)
Periodic trends – Atomic Radii
• As we move across a row (period) from left to right on the
periodic table, atoms become smaller as the atomic
number becomes larger. This increase in nuclear charge
allows the nucleus to pull in the electrons more tightly
and thereby reduce atomic size (radius).
• As we move down a column on the periodic table, elements
contain more electrons and more energy levels become
populated resulting in an increase in atomic size
(radius). Remember that completing a period on the
periodic table results in a completed energy level within
the atom.
Periodic Trends – Atomic Radii
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SIZE OF ATOMS DECREASES
Periodic Trends - Ionic Radii
Metal atoms lose electrons to form ions so they are
smaller than the original atoms. In a sodium atom,
the last electron is in the 3rd energy level, but when
it is lost, the outer shell is now the second level.
Nonmetal atoms gain electrons to form ions. Since
the number of protons doesn’t change, the electrons
can’t be held as tightly and they are able to move
further away.
Anions in the same period are larger than cations in
that row.
Periodic Trends – Ionic Radii
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2e
8e
Na+1 has 2 filled energy levels
+11
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+19
2e
8e
8e
K+1 has 3 filled energy levels
Periodic Trends – Ionic Radii
+9
The fluoride ion has 9 protons attracting the
the 10 electrons so there is more attraction
2e
8e
+7
2e
The nitride ion (N-3) has only 7 protons attracting 10 electrons so the
electrons are not held as tightly and the ion is larger than the fluoride
ion.
Periodic Trends – Ionic Radii
Why is this important ?
Excellent question – glad you asked.
Explaining a lot of bonding and chemistry deals
with two ideas.
1. Electronic Factors – Chemistry occurs
because of the charge factors, this is why it
is NaCl and not NaCl2
2. Steric Factors – Chemistry occurs because
of the size of molecules, just like in our
macro world. Medicines and body
chemistry use this a lot.
?
Periodic Trends – Ionic Radii
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SIZE OF IONS INCREASES
Periodic Trends – Ionization Energy
8e
1e
2e
+11
1e
+19
2e
8e
18e
The outer electron
for the sodium ion
is in the 3rd energy
level so it is closer
to the nucleus than
the outer electron
for the potassium
ion which is in the
4th energy level.
The further away
from the nucleus,
the less force of
attraction and the
easier it is to
remove that
electron.
Periodic Trends – Ionization Energy
+9
2e
Fluorine has two options to
become an ion. It can gain 1 e-1
to have a filled second shell or it
can lose 7e-1 to have a filled first
shell. It will always be the choice
that deals with the lower number
of electrons.
7e
1e
8e
+11
2e
Sodium can either lose a single
electron or gain 7 electrons to
achieve a filled outer shell.
Remember that it is always
deal with the lower number of
electrons so Sodium will lose
one electron and in this case
form a positive ion.
Periodic Trends – Ionization Energy
Successive Ionization Energies
For a sodium ion to be formed, only one electron has to be
removed, and it takes energy to remove the electron because
it doesn’t just happen on its own. This energy is called the
Ionization Energy.
For a magnesium ion to be formed, two electrons have to be
removed. It would be simple if we can simply double the
Ionization Energy but it doesn’t work that way. We need to
have an Ionization Energy for the 2nd electron. After the first
electron, the others are called successive ionization energies.
Different factors affect the value of the these energies and will
be described on the next slide.
Periodic Trends – Ionization Energy
Successive Ionization Energy
1. Distance from the nucleus. The closer the e-1 is to the
nucleus the more energy is needed to remove it.
2. Proton to electron ratio.
The more protons present in
the nucleus, the more attraction and the more energy is
needed to remove an electron.
3. Filled and half-filled sets of orbitals.
Filled and halffilled sets of orbitals are more stable and therefore take
more energy to remove an electron from them.
4. Shielding effect. Since magnetic attraction can’t move
through magnetic material, electrons in inner shells, can
block the attraction to the electrons in the outer shell,
making it easier to remove those electrons.
Periodic Trends – Ionization Energy
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Across a row, the Ionization Energy increases.
Down a column, the ionization energy decreases.
Periodic Trends – Ionization Energy
Successive Ionization Energies
• The Blue line occurs when the next electron being removed is
from an inner shell.
Periodic Trends – Electron Affinity
• Elements which are more nonmetallic (to the
left & up on the periodic table) have greater
electron affinity.
• Those which are more metallic (to the right &
down on the periodic table) have lower
electron affinity.
Periodic Trends – Electron Affinity
• Across each row, electron affinity increases.
• Down a column, electron affinity decreases.
Periodic Trends - Electronegativity
• Electronegativity is the ability of an atom to grab onto the
shared electrons in a bond.
• Flourine has the highest electronegativity value of 4.0
• This concept was developed by Linus Pauling (2
unshared Nobel Prizes). It was devised by comparing
the different bonds to each other, then when fluorine was
discovered to have the highest value he assigned it a
value of 4. There are no units !
• As you move away from Fluorine, the values get lower.
Periodic Trends – Electronegativity (En)
• Across each row, electronegativity increases.
• Down a column, electronegativity decreases.