Transcript Ch # 6 - Solano Community College

Ch # 6
Electronic Structure and
Chemical Periodicity.
The Periodic Law:
 It states that when elements are arranged in
increasing atomic number, the elements with
similar chemical behaviors occur
periodically.
The Periodic table:
 It is a tabular arrangement of elements in
order of increasing atomic number.
Elements having the same chemical
behaviors are grouped together in a vertical
column called a group.
The Periodic table:
 Each element is represented in a square
box, which contains:
 Symbol, atomic number, atomic mass
number of an element.
Periods and Groups of Elements:
 Period: A horizontal row of elements.
 There are 7 periods.
 The first period contains only two elements
H and He.
 Groups: A vertical column in the periodic
table.
 All elements in same groups have similar
chemical properties.
Periods and Groups of Elements:
 There are 18 groups.
 Group 1A= alkali metals. Except H. React
violently with water.
 Group II A= alkaline Earth metals. Do not
react in water.
 Group VII A=Halogens. Very reactive
colored gases.
 Group VIII A= Noble or inert gases. Very
unreactive
Periods and Groups of Elements:
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B groups= Transition elements.
Extension of period 6=Lanthanides.
Extension of period 7= Actinides.
The metals lie to the left of the table.
Nonmetals to the right. They are separated
by a step up ladder.
 In between this ladder are the metalloids.
The Shape of the Periodic Table:
 Lanthanides, Actinides.
The Energy of an electron:
 1. subatomic particle.
 2. They have very little mass compared to
proton and Neutrons.
3. Located outside the nucleus.
 4. Move around the nucleus in a volume that
defines the Size of the atom.
The Energy of an electron:
 In 1926 Schrodinger showed that laws of
quantum mechanics could be used to
characterize the motion of electrons.
 A quantized property is a property that can
have only certain values.
 The energy of an electron is quantized, only
certain behavior patterns are allowed.
Electron Shells
 Electrons with higher energy have higher
velocity and thus they move farther away
from the nucleus.
Electron shell
 A region in space about a nucleus that
contains electrons that have approximately
the same energy and that spend most of
their time approximately the same distance
from the nucleus.
Electron shell
 “n” is used to identify each electron shell.
 Electron energy increases as its distance
from nucleus increases.
 Shell energy capacity = 2n2, where n is
shell number.
 7 shells maximum.
 Shell # 1 has 2e, 2 has 8 es, 3 has 18 es, 4
has 32 es.
Electron Subshells:
 A region of space within an electron shell that
contains electrons that have the same energy.
 Number of subshells in a shell=n, n= shell number.
 The letters s, p, d, f in order indicate energies of
the subshells.
 S=2 es, p=6 es, d=10 es, f=14 es.
 Total number of electrons in shell 1=_______,
shell 2=____ shell 3=___ shell 4=___-.
Electron orbitals:
 A region of space within an electron subshell
where an electron with a specific energy is
most likely to be found.
 S subshell=1 orbital, p subshell=3 orbitals, d
subshell=5 orbitals, f subshell=7 orbitals.
 Maximum number of electrons in a subshell
is always 2.
 S orbital=spherical, p orbital =dumbbell
shaped.
Electron Spin
 : Property of an electron associated with its
spinning on its own axis.
 Pauli's exclusion Principle: The maximum
number of electrons in any orbital is two and
they are spinning in the opposite directions.
Electron Configurations
 A statement of how many electrons an atom
has in each of its subshells.
Aufbau Principle
 : It states that electrons normally occupy
electron subshells in an atom in order of
increasing subshell energy.
 Subshells are filled in order of increasing
energy.
Aufbau Diagram:
 Listing of electron subshells in the order in
which electrons occupy them.
Orbital Diagrams
 Two principles to be considered are The
Aufbau’s principle and Hund’s rule.
 A diagram that shows how many electrons
an atom has in each of its occupied electron
orbitals.
Hund’s Rule
 It states that when electrons are placed in a
set of orbitals of equal energy the order of
filling the orbitals is such that each orbital
will be occupied by one electron before any
orbital receives a second electron. This
minimizes the repulsion between the
electrons.
Orbital Diagrams
 Paired electrons: Two electrons of opposite
spin present in the same orbital.
 Unpaired electron: A single electron in an
orbital.
Orbital diagram
 Paramagnetic atom: An atom that has an
electron arrangement containing one or
more unpaired electrons.
 Diamagnetic atom: It is an atom that has an
electron arrangement in which all electrons
are paired.
Electronic configurations and The
periodic Law
 Chemical properties repeat themselves in a
repeated manner because electronic
configurations repeat themselves.
 Group number indicates the number of valence
electrons in atom.
 Valence electrons are the electrons that can loose,
gain or be shared in chemical reactions.
 Group 1=1 valence electron, group 7= 7 valence
electrons.
Electronic Configurations and The
Periodic Table
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S area has 2 columns.
P area has 6 columns.
D area has 10 columns.
F area has 14 columns.
Electronic Configurations and The
Periodic Table
 Distinguishing Electron: Last electron added
to the element’s electronic configuration
when the configuration is written according
to Aufbau principle.
 All elements in the first column of a specific
area contain 1 electron, second column
contains 2 electrons ------.
Electronic Configurations and The
Periodic Table
 Shell number=period number.
 For d area shell number=period number-1.
 For f area shell number=period number-2.
Classification Systems for the
Elements:
 A noble gas element: group VIII A. All
elements are gases. Do not react.All have 8
electrons around them , other than He.
 A representative element: Located in s area
or first 5 columns of the p area.
 Transition element: Element located in d
area
 Inner transition element: Located in the f
area of periodic table.
Based on physical properties:
 Metals: luster, thermal conductivity, electrical
conductivity, malleable, ductile.
 All metals are solid , except Hg.
 High density and high melting points.
 Ex: Al, Fe. Cu, Zn, Ag, Au.(91 elements)
 Left of periodic table, zigzag line
Based on physical properties:
 Nonmetals: no luster, not malleable, not
ductile, not good conductors.
 Gases at RT, except: Br-liquid.
 Lower densities, low Melting points.
 Ex: C,S, P.(22 elements)
 Right of periodic table, zigzag line.
 Earth’s crust contains: O,Si,H.
Chemical Periodicity:
 The variation in properties of elements as a
function of their positions in the Periodic
Table.
Metallic and Nonmetallic Character:
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Metallic character increases right to left, in
a period.
It increases from top to bottom in a group.
Nonmetallic character increases from left
to right in a period.
Nonmetallic character increases from
bottom to top in a group.
Metalloid:
 Element that possess properties both of
metals and nonmetals. Ex: Si, Ge Sb
Semiconductor:
 An element that does not conduct electric
current at room temperature but does so at
higher temperature.
Atomic Size:
 Unit for atomic radii is picometer.
 Range is 50-200 pm.
 Atomic radii decreases from left to right
within a period.
 Atomic radii increases from top to bottom
within a group.