Transcript ch 8 periodic properties power point

Periodic properties of the
elements
Patterns of main group elements
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Atomic size
Ionic size
Ionic radii
Chemical reactivity
Atomic size
• Size of atom increases in any group as you go
down the column because the valence
electrons are found in energy levels farther
from the nucleus.
• Size of atom decreases across a period. The
addition of protons “pull in” the electrons
from the same energy level.
Ionic size
• Important factor for chemical reactivity,
solutions, and structure
• Metallic Ions (groups 1-3 that lose valence
electrons) form are smaller than original element
because the remaining electrons are at a lower
energy level are attracted more strongly to the
nucleus.
• Nonmetallic ion (groups 5-7 that gain valence
electrons) but the nuclear charge doesn’t
increase so the electrons are held less tight and
the ionic radii is larger than neutral atom
Pattern in ionic radii
• Ionic radii increases down the table in a group
because of the increasing distance of the
valence electrons.
Main group reactivity
• Elements that lose electrons (bonding) the
larger the atom, the more readily it gives up
electrons, the more reactive. Cesium most
reactive of metals.
• Elements that gain electrons, the larger the
atom, the less the attraction for the electrons,
the less reactive. It’s more reactive smaller.
Fluorine most reactive of nonmetals.
Alkali metal
• Group 1: Li, Na, K, Rb, Cs, Fr.
• Soft, silvery – white metals, good conductors heat and
electricity, highly reactive – not found free in nature
• Lose s valence electron to form +1 ion (like previous
noble gas)
• Cs is most reactive metal
• Reacts with water to form hydroxide (base / alkaline)
• Na, K supply positive ion for transmitting nerve
impulse for muscle contraction
• K essential nutrient for plants
Alkaline Earth Metals
• Group 2: Be, Mg, Ca, Sr, Ba, Ra
• +2 ion, less reactive than alkali, but still too
reactive to be found free in nature.
• Mg alloys are used in jet engines, MgO
protects from further reaction with oxygen.
Mg is needed for photosynthesis, Ca needed
for bones Hydroxyapatitie Ca5(PO4)3OH.
• Sr is used in fireworks, bright red
Group (1)3
• B (metalloid), Al, Ga, In, Tl are metals, less
reactive than previous, silvery, soft, tend to share
electrons instead of forming ionic compounds.
• +3 ion, Al most abundant metallic element in
Earth’s crust, turns to oxide preventing further
reaction. Hall-Heroult process removes from ore,
many items made of Al
• B found in cleaning solutions
• Ga melts in your hand
Group 14 – carbon family
C (nonmetal),Si and Ge (metalloids), Sn, and Pb
(metals)
+4 ,Share electrons during reactions, Sn / Pb lose
electrons
C – living things / food, pencil lead, diamond
Si – Sand (SiO2), Glass, sealant, ceramics,
semiconductors
Sn – protective coating on steel can for food
storage, bronze, solder, pewter, foil
Pb – batteries, pewter
Group 15
• N, P (nonmetals),As, Sb (metalloids), Bi (metallic)
• -3, gain 3 electrons
• N – proteins, DNA, RNA, 78% of air – not usable
so bacteria on legumes it to ammonia (fertilizer)
and nitrate, lightning (NO)
• P – Phosphate group (PO4-3), ATP, red matches
• As – with Ga for electronics
• Sb – improves hardness and corrosion resistance
in alloys.
Group 16
• O, S, Se, Te (nonmetals) Po (metalloid)
• -2 gains 2 electrons
• O – most abundant element, 21% atmosphere,
water, ozone – pollutant lower “smog” protect
from UV in upper atmosphere. Hydrogen
peroxide (H2O2),
• Sulfur – Frasch process, sulfuric acid – batteries,
rubber
• Se – security and mechanical devices,
photocopier
Group 17
• Halogen: F, Cl, Br, I, At,
• -1 gains 1 electron, very reactive and not
found free, diatomic – bound to itself
• F most reactive, toothpaste,
• I antibacterial, thyroid gland
• Cl – kill bacteria in water, bleach
• Br – photographic film – light sensitive coating
on film.
Group 18 – Noble gas
• He, Ne, Ar, Kr, Xe and Rn
• Full valence shell, inert. Kr and Xe have F
compounds
• He- used in balloons because “lighter than air”
and less reactive than Hydrogen.
Trends in properties of transitional
elements
• Have high melting point and boiling point
(except zinc column); increases from Group 3
to maximum group 5/6 and decrease across
the remainder. Tungsten – highest metal,
Mercury – lowest, liquid at room temperature
• Have many oxidation state due to involvement
of the d electrons (close energy to s orbital) in
chemical bond (only heavy main group display
this property)
Trends in atomic size of transitional
elements
• Similar trend to main group, just not as
dramatic.
• Atomic radii increase as go down the group
• Atomic radii decreases at you go down a
period.
Iron
• Needed in biology – Hemoglobin
• Magnetic
• Separated from Ore (oxides) in blast furnace, to
produce pig iron where slag is drawn off.
• Iron with additives (carbon or transitional) to give
steel with different properties. Surgical steel is
hardest.
• Heat treating – iron reacts with carbon to form a
carbide that dissolves in steel.
• Damascus steel
Other transitional elements
• Iron triad – Fe, Co, Ni
• Platinum group – Ru, Rh, Pd, Os, Ir, Pt: used as
catalyst to speed up reactions
• Coinage metals- Cu, Ag, Au: used for coins
because malleable, less reactive, rare
• Chromium – Corrosion – resistance, self
protecting, variety of colored compounds
• Zinc – corrosion – resistance, galvanize –
surface coating of steel, Brass when add Cu.
Inner transitional elements
• Little change in atomic size in period 5 and 6
so they have similar properties
• Cerium – misch metal alloy, flint for lighters,
glass polish
• Neodymium – welder’s shield
• Some in control rods – nuclear (absorb
neutrons)
• electronics
Actinides
• Uranium – radioactive element for nuclear
fuel
• Plutonium – nuclear fuel, power source in
pacemakers and buoys.