Introducing the Elements
The Element Song
1869: Dmitri Mendeleev
• Russian chemist
• Arranged elements in
tabular form so that
elements with similar
properties were in the
same column
• When listed in order
by mass, elements
generally repeat
properties in groups
of 8 (Law of Octaves)
The First Periodic Table
• Most tables at the time listed elements by mass
• Mendeleev also arranged elements by mass, but
left several “holes” in his table and occasionally
reversed the order of elements to fit the
properties of others in that column
• The “holes” were later filled in with newly
discovered elements that had the properties
predicted by Mendeleev’s table.
• The reason for the reversal of elements was
explained later by Henry Moseley, who noted
that the elements were in order by atomic
number (number of protons) rather than by mass
Hydrogen
• Most abundant element in
the universe
Why?
• Makes up most the mass
of stars
• Can be H+ (hydrogen
ion) or H- (hydride ion)
• Used in Fuel Cells: How
Stuff Works
• In Fusion, H is converted
to He
Alkali Metals: Li, Na, K, Rb, Cs, Fr
• Most reactive of the
metals, +1 ions
• Stored under kerosene or
mineral oil
• Na and K most important
• Na2CO3 and NaHCO3 two
important compounds
• K is an important plant
nutrient (macronutrient)
• Fertilizers: N-P-K
Total Molar Composition of Seawater (Salinity = 35)[7]
Compone
nt
Concentration
(mol/kg)
H2O
53.6
Cl−
0.546
Na+
0.469
Mg2+
0.0528
SO2−
0.0282
4
Ca2+
0.0103
K+
0.0102
CT
0.00206
Br−
0.000844
BT
0.000416
Sr2+
0.000091
F−
0.000068
Alkaline Earth Metals: Be, Mg, Ca, Sr, Ba, Ra
• Harder, more dense,
and less reactive than
alkali metals
• Ca, Sr, and Ba most
alike
• Hard Water: Ca2+
and Mg2+ ions
• Epsom salt: MgSO4
Boiler Scale
…..more on the alkaline earths
• CaCO3 is limestone
becomes marble
• Limestone is most
abundant rock in the
earth’s crust
• CaO “Lime” or
“quicklime”
• CaSO4 “Plaster of
Paris” (building
material)
Plaster of Paris footprints
Aluminum Group: B, Al, Ga, In, Tl
• Aluminum by far the most important
• Third most abundant element in the
earth’s crust
• Important metal: abundant, light weight,
strong
• Al2O3 coating prevents corrosion
Carbon Group: C, Si, Ge, Sn, Pb
•
•
•
•
Very diverse group of elements
C is the basis for organic compounds
CO2 and CO3-2 inorganic carbon
CO2 one of the earliest gases in the
atmosphere
• Carbon cycling one of the most important
• Two basic parts: (1) photosynthesis (2)
respiration
Disrupting the carbon cycle
•
CO2 is a greenhouse
gas (GWP=1)
Increasing
concentration by:
•
1.
2.
Burning fossil fuels
Removing vegetation
•
Preindustrial 1800:
280 ppm
1959: 316 ppm
2010: 388 ppm
2011: 391 ppm
•
•
•
Growing CO2 Warms the Earth
• Greenhouse Effect is essential for Life!
– Earth’s radiative balance (solar input vs. IR
output) leaves <TEarth> ~ – 20°C
• Almost all water would be ice everywhere.
• But Life requires ℓiquid water!
– H2O(g) and CO2 absorb outbound IR and
reradiate it omnidirectionally.
• So Earth intercepts ~½ that absorbed IR and
gains <T> to +15°C.  H2O(ℓ) & we exist.
Venus, the Runaway
Greenhouse
• Being closer to the sun, Venus intercepts
twice the solar flux of Earth.
• But it is twice as reflective (albedo), so its
temperature would be ~ –29°C.
• But it’s surface T averages +435°C!
• 90 atm at the surface, mostly CO2
Keeling Curve
Silicon - Si
• Second most
abundant element in
the Earth’s crust
• Found in clay, sand,
sandstone, silica rock,
quartz, other minerals
• Many different
bonding combinations
• Is a semiconductor
(Silicon Valley)
Tin (Sn) and Lead (Pb)
• Many Industrial Uses
• Pb is a “heavy metal” and is toxic to many
organs in the human body
• Impedes the development of the nervous
system
• Taken out of gasoline in the late 1970’s
and removed from most paints
Ozone
• Ozone absorbs much of the radiation
between 240 and 310 nm.
• It forms from reaction of molecular oxygen
with the oxygen atoms produced in the upper
atmosphere by photodissociation (< 242 nm).
O + O2  O3
Ozone Depletion
In 1974 Sherwood Rowland and Mario
Molina (Nobel Prize, 1995) discovered that
chlorine from chlorofluorocarbons (CFCs)
may be depleting the supply of ozone in the
upper atmosphere.
Chlorofluorocarbons
CFCs were used for years as aerosol
propellants and refrigerants.
Mostly = CFCl3, CF2Cl2.
They are not water soluble (so they do not
get washed out of the atmosphere by
rain)
and are quite unreactive (so they are not
degraded naturally).
Chlorofluorocarbons
• The C—Cl bond is easily broken,
though, when the molecule absorbs
radiation with a wavelength between
190 and 225 nm.
• The chlorine atoms formed react with
ozone:
Cl + O3  ClO + O2
Chlorofluorocarbons
In spite of the fact that the use of CFCs in
now banned in over 100 countries, ozone
depletion will continue for some time
because of the tremendously unreactive
nature of CFCs.
Sulfur
• Sulfur dioxide is a byproduct of the burning
of coal or oil.
• It reacts with moisture
in the air to form
sulfuric acid.
• It is primarily
responsible for acid
rain.
Sulfur
• High acidity in rainfall
causes corrosion in building
materials.
• Marble and limestone
(calcium carbonate) react
with the acid; structures
made from them, erode.
Sulfur
• SO2 can be
removed from flu
gases by injecting
powdered
limestone which is
converted to
calcium oxide.
• The CaO reacts
with SO2 to form a
precipitate of
calcium sulfite.
This process = “scrubbing”
Carbon Monoxide
• Carbon monoxide
binds preferentially to
the iron in red blood
cells.
• Exposure to CO can
lower O2 levels to the
point of causing loss
of consciousness and
death.
Carbon Monoxide
• Products that can
produce carbon
monoxide must contain
warning labels.
• Carbon monoxide is
colorless and odorless,
so detectors are a good
idea.
Nitrogen Oxides
• What we recognize as
smog, that brownish
gas that hangs above
large cities like Los
Angeles, is primarily
nitrogen dioxide, NO2.
• It forms from the
oxidation of nitric oxide,
NO, a component of
car exhaust.
Photochemical Smog
Nitrogen oxides react with
water to form nitric acid,
contributing to acid rain.
Smog also contains
ozone, carbon
monoxide,
hydrocarbons, and
particles.
Bonding: Influences
•
•
•
•
•
Valence Electrons
Nuclear Charge
Atomic Size/Radius
Distance between attractions
Screening or Shielding Effect
Valence Electrons
Core Configurations
• Why? – Shows/focuses on the valence
electrons.
• Write the configuration for arsenic.
• 1s22s22p63s23p64s23d104p3
• or
• [Ar] 4s23d104p3
• How many valence electrons?
Atomic Radius: How is it measured?
• Half the distance between nuclei of two
covalently bonded atoms of the same
element.
• Why not just measure from the nucleus to
the outer edge of the atom?
Atomic Radius
Radius trends
• Group trend?
Radius increases down a group
• Why?
Adding new energy levels
• Period trend?
Radius decreases across a period
• Why?
Increasing nuclear charge has the
effect of pulling electron cloud closer.
Ions and their formation
• Cations
• Formed by the loss of
electrons
• Positively charged
• Usually formed from
metals
• Are always smaller
than the atom they
are formed from
• Anions
• Formed by the gain of
electrons
• Negatively charged
• Usually formed from
nonmetallic elements
• Are always larger
than the atom they
are formed from
Ionization Energy
• The energy required to remove an electron from
an isolated, neutral, gaseous atom.
• First ionization energy – energy required to
remove a first electron from an atom.
• Second ionization energy – energy required to
remove a second electron from an atom.
• Third ionization energy - ????
• Etc . . . .
First Ionization Energies
First Ionization energies
• Group trend – IE1 decreases down a
group. Why?
• Valence electrons are further from the
nucleus and the shielding effect is greater
down a group.
• Shielding effect – occurs when core
electrons “shield” or interferes with the
attraction that the nucleus has for the
valence electrons.
. . . IE cont. . . .
• Period trend – IE1 is larger as you move
across a period, left to right. Why?
• Atoms are smaller so valence electrons
are closer to the nucleus and . . . . .
• . . . the nuclear charge is greater with no
change in shielding effect (electrons are
going in the same energy level)
Ionization Energy Increasing Trend
Periodic Table
Successive Ionization Energies
Where do the largest jumps occur for each
Element and why do you think this happens?
Electronegativity
• A measure of the ability of an atom to
attract electrons to itself when bonded to
other atoms.
• Trends in electronegativity are the same
as ionization energy and the reasons why
are essentially the same too.
Electronegativities
Electron Affinity
• The amount of energy released or gained
when an atom receives an electron.
• When this happens a negatively charged
ion, called an anion, forms.
Electron Affinity
Notice what groups have
(-) negative affinities and what
groups have (+) positive affinities
(negative values are shown here as
above zero.)
A negative affinity means energy
is released and a positive affinity
means that much energy is gained
when an atom acquires and electron.
1. Place these elements in order of increasing:
Ge, P, N, and Si
(a) atomic radius
(b) first ionization energy
(c) electronegativity
2. Write the core configuration for the following
elements: S, Ca, Sn
3. How many valence electrons does each
element in #2 have?