Transcript Electron Energy Level

Unit 2 – Electrons and
Periodic Behavior
Cartoon courtesy of NearingZero.net
Mendeleev’s Periodic Table
• By the mid-1800s, about 70
elements were known to exist
• Dmitri Mendeleev – a Russian
chemist and teacher
• Arranged elements in order of
increasing atomic mass
• Thus, the first “Periodic Table”
A better arrangement
• In 1913, Henry Moseley –
British physicist, arranged
elements according to
increasing atomic number
• The arrangement used today
Group or Family
Period
The Periodic Table
Group or
family
Period
Periodic Table
Periodic table is divided into 3
classes
Metals
Non metals
Metalloids
The horizontal rows are called periods
while the vertical columns of the
periodic table are called Groups or
Families
Properties of Metals
 Metals are good
conductors of heat and
electricity
 Metals are malleable
 Metals are ductile
 Metals have high tensile
strength
 Metals have luster
Examples of Metals
Potassium, K
reacts with
water and
must be
stored in
kerosene
Copper, Cu, is a relatively soft
metal, and a very good electrical
conductor.
Zinc, Zn, is
more stable
than potassium
Mercury, Hg, is the only
metal that exists as a
liquid at room temperature
Properties of Nonmetals
Carbon, the graphite in “pencil lead” is a great
example of a nonmetallic element.
 Nonmetals are poor conductors of heat and
electricity
 Nonmetals tend to be brittle
 Many nonmetals are gases at room
temperature
Examples of Nonmetals
Sulfur, S, was
once known as
“brimstone”
Graphite is not the only
pure form of carbon, C.
Diamond is also carbon;
the color comes from
impurities caught within
the crystal structure
Microspheres
of phosphorus,
P, a reactive
nonmetal
Properties of Metalloids
Metalloids straddle the
border between metals
and nonmetals on the
periodic table.
 They have properties of both metals and
nonmetals.
Metalloids are more brittle than metals, less
brittle than most nonmetallic solids
 Metalloids are semiconductors of electricity
 Some metalloids possess metallic luster
Silicon, Si – A Metalloid
 Silicon has metallic luster
 Silicon is brittle like a nonmetal
 Silicon is a semiconductor of
electricity
Other metalloids include:





Boron, B
Germanium, Ge
Arsenic, As
Antimony, Sb
Tellurium, Te
The Properties of a Group:
the Alkali Metals
Easily lose valence electron
(Reducing agents)
React violently with water
Large hydration energy
React with halogens to form
salts
(valence electrons are electrons
in the outermost shell of an
atom)
Properties of Alkaline earth metals
• They are the group II A elements
• Denser, harder and stronger than
Group I A elements but less reactive
• Too reactive to be found pure in nature
Halogens and Noble Gases
• Halogens are the most reactive of the non
metals.
• They are the group VII A elements
• The noble gases are the group VIII A
elements.
• They are also called inert gases because
they undergo very few reactions.
Periodic Law
When elements are arranged in order of
increasing atomic number, there is a
periodic repetition of their physical and
chemical properties.
The Bohr Model of the Atom
I pictured
electrons orbiting
the nucleus much
like planets
orbiting the sun.
Neils Bohr
But I was
wrong! They’re
more like bees
around a hive.
WRONG!!!
Electron Energy Level (Shell)
Generally symbolized by n, it denotes the
probable distance of the electron from the
nucleus.
Number of electrons
that can fit in a shell:
2n2
An orbital is a region within an energy level where
there is a probability of finding an electron. This is a
probability diagram for the s orbital in the first
energy level…
Orbital shapes are defined as the surface that
contains 90% of the total electron probability.
Energy Levels, Sublevels, Electrons
Energy
Level
(n)
Sublevels in
main energy
level
(n sublevels)
Number of
orbitals per
sublevel
Number of
Electrons
per sublevel
Number of
electrons per
main energy
level (2n2)
1
s
1
2
2
2
s
p
1
3
2
6
8
3
s
p
d
1
3
5
2
6
10
18
4
s
p
d
f
1
3
5
7
2
6
10
14
32
Orbital filling table
Irregular conformations of Cr and Cu
Chromium steals a 4s electron to half
fill its 3d sublevel
Copper steals a 4s electron to FILL
its 3d sublevel
Periodic Trends
How do properties of elements
change as you go across a
periodic table?
Determination of Atomic Radius:
Half of the distance between nuclei in
covalently bonded diatomic molecule
"covalent atomic radii"
Periodic Trends in Atomic Radius
Radius decreases across a period
Increased effective nuclear charge due
to decreased shielding
Radius increases down a group
Addition of principal quantum levels
Table of
Atomic
Radii
ION
• An atom or a group of atoms that has a
positive or negative charge are called ions.
• Atoms get a positive charge when they
lose electrons
• Atoms get a negative charge when they
gain electrons
• Ionization is the process that results in the
formation of an ion.
Ionization Energy - the energy required to
remove an electron from an atom
Increases for successive electrons taken from
the same atom
Tends to increase across a period
Electrons in the same quantum level do
not shield as effectively as electrons in
inner levels
Irregularities at half filled and filled
sublevels due to extra repulsion of
electrons paired in orbitals, making them
easier to remove
Tends to decrease down a group
Outer electrons are farther from the
nucleus
Table of 1st Ionization Energies
Electronegativity
A measure of the ability of an atom in a chemical
compound to attract electrons
Electronegativities tend to increase across
a period
Electronegativities tend to decrease down a
group or remain the same
Periodic Table of Electronegativities
Summation of Periodic Trends
Ionic Radii
Cations
Positively charged ions formed when
an atom of a metal loses one or
more electrons
Smaller than the corresponding
atom
 Negatively charged ions formed
when nonmetallic atoms gain one
Anions
or more electrons
 Larger than the corresponding
atom