Periodic Trends
History of the Periodic Table
Click to add an outline
1817 - Johann Dobereiner grouped elements
into triads
1869 - Dmitri Mendeleev and Lothar Meyer
published near identical tables
1913 – Henry Moseley reordered tables based
on atomic number
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2
Effective Nuclear Charge
Properties of atoms we need to understand
how strongly valence electrons are held
Coloumb's law of attraction
Sizes of Atoms and Ions
F = k·q1·q2
r2
Atoms do not have a
sharply defined
exteriors
Non-bonding / Van der
Waals Radii
Covalent Radius = ½
the distance between
2 nuclei
Used radius to
estimate bond length
Effective Nuclear Charge = Pull of nucleus
Zef f = Z – S
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Atomic Radius
Estimating Bond Length Example
5
Natural gas used in home heating and cooking
is odorless. Because natural gas leaks pose the
danger of explosion or suffocation, various
smelly substances are added to the gas to
allow detection of a leak. One such substance
is methyl mercaptan, CH3SH, whose structure is
shown in the margin. Predict the lengths of the
C—S, C—H, and S—H bonds in the molecule.
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Estimating Bond Length Practice
Trends in Atomic Radius
Which bond length will be greater, the P—Br
bond in PBr3 or the As—Cl bond length in
AsCl3?
Atomic Radius increases as you move down a
column
Principle quantum number (n) increases
Shielding increases
Atomic Radius decreases as you move across
a row from left to right
Zef f increases
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Arranging Atoms in Size Practice
Trends in Ionic Size
Arrange the following atoms in order of
increasing size: P, S, As, Se
Arrange the following atoms in order of
increasing size: Na, Be, Mg
Ionic size based on how far apart ions are in ionic
compounds
Size determined by:
Nuclear charge
Number of electrons
Orbitals occupied
Cations – smaller than parent atom
Anions – larger than parent atom
For ions with same charge, size increases as you move
down a group
Isoelectronic – same number of electrons
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Arranging Ions in Size Practice
Ionization Energy
Arrange these atoms and ions in order of
decreasing size: Mg2+ , Ca2+ , and Ca.
Defn: Energy needed to remove an electron
from the ground state of a gaseous atom/ion
Which of the following atoms and ions is the
largest: S2- , S, O2-
I1, I2, .....
Successive IE become higher and higher
Increases in IE occur when removing electrons
from inner shells and stable configurations
Arrange the following ions in order from
smallest to largest: Mg2+ , O2- , Na+,Al3+ , F11
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Ionization Energy Practice Pt 1
Periodic Trends in Ionization Energy
Which of the following elements will have the
largest second ionization energy? Sodium,
Calcium, Phophorus
Which will have the greater third ionization
energy, Ca or S?
1s t ionization energy increases as we go from
left to right along a period
1s t ionization energy decreases as we go from
top to bottom
The IE's of representative elements vary more
than d-block and f-block elements
Why?
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Ionization Energy Practice Pt 2
Electron Configuration for Ions
Referring to a periodic table, arrange the following
atoms is order of increasing first ionization energy:
Ne, Na, P, Ar, K.
Predict which of the following atoms – B, Al, C, or Si
– has the lowest first ionization energy and which
has the highest ionization energy.
Cations lose valence electrons
Li 1s22s1 Li+1 1s2
Fe [Ar] 4s23d6 Fe2+ [Ar]3d6
Fe2+ [Ar] 3d6 Fe3+ [Ar]3d5
Anions gain electrons to fill the valence shell
S [Ne] 3s23p4 S2- [Ne]3s23p6
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Electron Configuration for Ions
Practice
Electron Affinity
Write the electron configuration for the following
ions: Ga3+ , Cr+3 , Br -, Mn7+ , Cu2+ , Cu+1
Energy change that occurs when electrons are
added to a gaseous atom
For most atoms E is released when electrons
are added
IE = ease of losing e-'s
EA = ease of gaining e-'s
When EA >> 0 the ion does not form
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Cl + e- Cl- E = -349kJ/mol
Ar + e- Ar- E > 0
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Metals, Non Metals, Metalloids
Most elements are metals
Are located to the left of the staircase line
Metallic character increases and Properties
Non-metals
Metals
Are located to the right of the staircase line
Metalloids
Form the staircase line
B, Si, Ge, As, Sb, Te, At
Shiny (have luster)
Various colors
Malleable/Ductile
Good conductors of heat and electricity
High Melting points
Form cations in solution
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Most metal oxides are ionic solids that are basic
–
CaO + H2O Ca(OH)2
–
NiO + 2HCl NiCl2 + H2O
Metals Cont.
Non Metals
Properties Cont.
Non metallic character increases and Properties
Have low IE
Easily oxidized by oxygen and acids
Do not have luster / various colors
Alkali have + charge
Low Melting Points
Alkaline Earth have +2 charge
Transitional Metals form more than one ion except
for Zn, Cd, and Ag
Most are solid at room temp. except who?
Solids are usually brittle, some are soft some are
hard
Poor conductors of heat and electricity
Form anions or oxyanions in aqueous solution
Metals + non metals = ionic compounds
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Non Metals Cont.
Trends for Active Metals
Properties Cont.
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7 Diatomic Elements
Have all three states of matter
Alkali Metals (Group IA)
Soft metallic solids
Low density
Silvery shiny
–
Gas – H2, N2, O2, F2, Cl2
Very conductive
–
Liquid – Br2
Low 1st IE
–
Solid – I2
Reacts with most non-metals
React with water to form H2 and metal hydroxides
React with oxygen to from metal oxides or metal peroxides
–
Form acid solutions
–
CO2 + H2O H2CO3
–
CO2 + NaOH Na2CO3 + H2O
–
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–
2M + H2 2MH, 2M + S M2 S
2M + H2O 2MOH + H2
4Li + O2 2 Li2O, 2Na + O2 Na2O2
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Trends for Active Metals Cont.
Flame Tests
Red
Alkaline Earth Metals (Group IIA)
Solids
High MP
Low 1st IE
Higher density (than IA)
Less reactive than IA
Heavy IIA metals give colors in flame tests
Yellow
Sodium compounds, even in trace amounts. A yellow flame is not indicative
of sodium unless it persists and is not intensified by addition of 1% NaCl to
the dry compound.
Green
Emerald: Copper compounds, other than halides. Thallium.
Blue-Green: Phosphates, when moistened with H2SO4 or B2O3.
Faint Green: Antimony and NH4 compounds.
Yellow-Green: Barium, molybdenum.
Blue
Azure: Lead, selenium, bismuth, CuCl2 and other copper compounds
moistened with hydrochloric acid.
Light Blue: Arsenic and come of its compounds.
Greenish Blue: CuBr2, antimony
Violet
Potassium compounds other than borates, phosphates, and silicates.
Masked by sodium or lithium.
Purple-Red: Potassium, rubudium, and/or cesium in the presence of
sodium when viewed through a blue glass.
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Reaction Predictions
Carmine: Lithium compounds. Masked by barium or sodium.
Scarlet or Crimson: Strontium compounds. Masked by barium.
Yellow-Red: Calcium compounds. Masked by barium.
Trends for Non Metals
Write the balanced equations that predict the
reactions of cesium with chlorine, waterm and
hydrogen.
Hydrogen
Placed in group IA b/c electron configuration
High 1st IE
Can be both cation and anion
Reactions btwn hydrogen and non metals are very
exothermic
Reacts w/ reactive metals to form metal hydrides
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Trends for Non Metals
Trends for Non Metals
Group VIA
Group VIIA - Halogens
All non metals
Oxygen
Each exists as a diatomic molecule
Fluorine and Chlorine are the most reactive
React w/ Ionic Halides
Dissolved in water to form acids
–
–
Goes from non metals to metals
–
Only gas in the group
Two major forms of oxygen: O2, O3
2-
2-
Oxygen anions – O , O2 , O
2
Sulfur has several allotropes
Group VIIIA – Noble Gases
All monotomic
–
S8 (yellow solid) most common
Usually found as metal sulfides
Non-reactive
–
Does not form anions as easily as
High 1st IE
–
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Homework
Ch. 7 – 15, 20, 24, 27, 31, 35, 37, 47, 49, 51,
55, 59, 61, 63
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