trends in the periodic table trend: direction or pattern p. 70-75
TRANSCRIPT
Trends in the Periodic TableTrends in the Periodic Table
trend: direction or pattern
p. 70-75
s, p, d and f blocks of the periodic table
gro
up
s
periods
“Long form” periodic table
• Electronic structures are related to the position of the elements on the periodic table– s-block: s orbitals are filled– p-block: p orbitals are filled, etc.
Zumdahl p. 322
Atomic number
• Increases from left to right (across periods)
• Increases from top to bottom (down groups)
• Period number: number of energy levels containing electrons
• Group: same valence shell electron configuration 1
2
34 56 7 89101112
131415161718
Group names
• 1: alkali metals (1 valence electron)
• 17: halogens (7 valence electrons)
• 18: noble gases (all electron shells filled, little chemical reactivity)
• periodicity: repeating of similar properties because of similar valence electron configuration
117
18Important Groups
Physical Properties in the PTE
Atomic and Ionic Radii
• Atomic radius: half the distance between the nuclei of two touching atoms
• Increases going down a group– Additional filled energy levels of electrons
• Decreases going across a period– More electrons = increased attraction to
positive nucleus
Increasing Atomic Radius
Atomic Radius Increases
Ato
mic R
adiu
s Increases
• Radius of an atom always decreases when it loses an electron (becomes a cation +)– A whole energy level may be lost, or– There is less electron-electron repulsion
(pushing away) between the electrons in different energy levels
• The radius of an atom always increases when it gains an electron (becomes an anion -)– Increased electron-electron repulsion pushes
the valence shell away from the nucleus.
Ionic radius examples
• K
• K+
• Cl
• Cl-
Ionization energy
• The amount of energy that is required to remove an electron from a gaseous atom
• Decreases going down a group– Valence electrons are further from the
nucleus, less “pull” from the protons
- +15 -
- -
-
-
- -
-
-
-
-
-
-
-+15
+13+5
Effective Nuclear Charge
• Charge exerted on each electron by the positively charged nucleus
- +15 -
- -
-
-
- -
-
-
-
-
-
-
-+15
+13+5
Ionization Energy
• Increases going across a period– Electrons on the same energy level are more
strongly “pulled” by the nucleus (which is increasing in positive charge)
+11 +12
Ionization Energy IncreasesIo
niz
atio
n E
ner
gy
Incr
ease
s
Electronegativity
• How strongly an atom attracts other electrons in a chemical bond (electron affinity)
• Decreases going down a group– Valence electrons are further from the nucleus, less
“pull” from the protons– Atoms increase in radius
• Increases going across a period– Electrons on the same energy level are more strongly
“pulled” by the nucleus– Atoms decrease in radius
Electronegativity IncreasesE
lect
ron
egat
ivit
y In
crea
ses
Other Physical Properties
• Melting Point
• Boiling Point
• Density
• Types of bonds formed
Chemical Properties
• Elements in the same group have similar chemical properties
Increasing atomic and
ionic radii
Incr
easi
ng io
niza
tion
ener
gy
Incr
easi
ng
elec
tron
egat
ivity
Increasin
g reactivity
Alkali metals• Soft, malleable (can be shaped) metals• Low melting points
– Can only contribute one electron to a bond – easily broken
• Low density– Largest atomic radius in the period
• Very chemically reactive– One valence electron, easily lost, + ion
• Tarnish quickly• Combine with O, Cl, Br to form ionic compounds
sodium
potassium
rubidium
cesium (l)
• All react with water to form a solution of metal hydroxide and hydrogen
• 2M(s) + 2H2O(l) 2M+(aq) + 2OH-(aq) + H2(g)
• M = alkali metal
sodium potassium
Reaction is alkaline (base)
• What trend in reactivity did you see as we moved down the group?
Increasing atomic and
ionic radii
Incr
easi
ng io
niza
tion
ener
gy
Incr
easi
ng
elec
tron
egat
ivity
Incr
easi
ng
rea
ctiv
ity
Halogens
• Very reactive non-metals– Need only one electron to fill valence shell
• All exist as diatomic molecules– Cl2, Br2, I2 (all colored)
• Slightly soluble in water – non-polar bonds
Halogens – colored diatomic molecules
fluorine pale yellow gas
chlorine yellow-green gas
bromine red-brown liquid
iodine black-purple solid
purple gas
• X2(aq) + H2O(l) H+(aq) + X-(aq) + HOX(aq)
– X = halogen– HOX = acid
• Ex: Chlorine: HOCl (HClO: chloric acid), used as a bleach, toxic to microbes, treats water
• all quite electronegative (high electron affinity)
• easily gain electrons to form anions– halide ions
• Ability to gain electrons decreases going down a group
• reactivity decreases going down a group
• Halogens combine with metals to produce ionically bonded salts containing a halide ion.– white and soluble in water colorless solutions
– insoluble: lead and silver compounds
– lead(II) iodide: bright yellowyellow precipitate
• Test for a halide ion by adding nitric acid, then a solution of silver nitrate– a precipitate indicates Cl-, Br-, or I-
compound color
AgF no precipitate
AgCl white, then purple/black in sunlight
AgBr off-white
AgI pale yellow
silver bromideused to print black and white photos
silver chlorideused to print black and white photos
silver iodideused to “seed the clouds” to make it rain
• Oxidant: In a reaction, a higher halogen will replace a lower halogen.
• NaCl(aq) + Br-
• NaBr(aq) + Cl- NaCl(aq) + Br-(aq)
Ionization Energy Increases
Atomic Radius Increases
Electronegativity Increases
Metallic Character Increases
Your questions…
Answered!
• Q: Why don’t the electrons crash into the nucleus?
• A: Electrons have lots of their own energy. E=hf due to their position around the nucleus. Electrons are constantly moving, very fast.
• This kinetic energy overcomes the positive attraction of the nucleus.
• A: How does temperature affect ionization energy?• Q: Temperature has no affect on ionization energy. Heat is
only powerful enough to change kinetic energy of a particle or molecule.
• Microwaves and radio waves can affect nuclear spin. Gamma rays and X rays can effect the nucleus and the inner electrons.
• Electricity does have an affect on ionization energy.
• Q: How does temperature affect the movement of the subatomic particles, specifically electrons?
• A: Temperature does not have enough energy to affect subatomic particle movement, only molecule movement.
• Q: Where does ionization energy come from?
• A: Electricity
• Q: If there is just one electron in a px orbital, can it be located everywhere, or just on one side of the orbital?
•A: It can be located anywhere. An orbital is an area of probability inside of which the electron will be found. Electrons are constantly moving very fast, and can be anywhere within their orbitals.
• Q: Why does ionization energy increase going across a period? Why, oh Why?!?
• A: The effective nuclear charge DOES change on each valence electron!
+11 +12ENC=+1
ENC=+2
Mid-term
• Tuesday, April 22– 14:40-16:10– Room 407 or 408
• 19 questions – short answer or calculations– 2 definitions
• Answer all parts of all questions• No dictionary/translator• Bring calculator, Periodic Table on test