Trends in the Periodic Table

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Trends in the Periodic Table

• trend direction or pattern
• p. 70-75

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s, p, d and f blocks of the periodic table
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Long form periodic table
groups
periods
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• 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.

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Zumdahl p. 322
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Atomic number

• Increases from left to right (across periods)
• Increases from top to bottom (down groups)

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• Period number number of energy levels containing
  electrons
• Group same valence shell electron configuration

1
18
2
13
14
15
16
17
3
4
5
6
7
8
9
10
11
12
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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

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Important Groups
1
18
17
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Physical Properties in the PTE
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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

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Increasing Atomic Radius
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Atomic Radius Increases
Atomic Radius Increases
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• 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.

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Ionic radius examples

• K
• K
• Cl
• Cl-

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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

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Effective Nuclear Charge
-
-
-
-
-
-

• Charge exerted on each electron by the positively
  charged nucleus

-
-
-
-
-
-
-
-
15
15
-
-
-
-
-
-
-
-
-
-
15
15
13
13
5
5
-
-
-
-
-
-
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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
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Ionization Energy Increases
Ionization Energy Increases
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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

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Electronegativity Increases
Electronegativity Increases
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Other Physical Properties

• Melting Point
• Boiling Point
• Density
• Types of bonds formed

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Chemical Properties
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• Elements in the same group have similar chemical
  properties

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Increasing atomic and ionic radii
Increasing ionization energy
Increasing electronegativity
Increasing reactivity
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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

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sodium
potassium
cesium (l)
rubidium
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• 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

Reaction is alkaline (base)
sodium
potassium
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• What trend in reactivity did you see as we moved
  down the group?

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Increasing atomic and ionic radii
Increasing ionization energy
Increasing electronegativity
Increasing reactivity
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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

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Halogens colored diatomic molecules
fluorine pale yellow gas
chlorine yellow-green gas
bromine red-brown liquid
iodine black-purple solid purple gas
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• 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

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• 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

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• 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 yellow precipitate

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• 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
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silver chloride used to print black and white
photos
silver iodide used to seed the clouds to make
it rain
silver bromide used to print black and white
photos
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• Oxidant In a reaction, a higher halogen will
  replace a lower halogen.
• NaCl(aq) Br- ?
• NaBr(aq) Cl- ? NaCl(aq) Br-(aq)

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Atomic Radius Increases
Ionization Energy Increases
Electronegativity Increases
Metallic Character Increases
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Your questions

• Answered!

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• Q Why dont the electrons crash into the
  nucleus?
• A Electrons have lots of their own energy. Ehf
  due to their position around the nucleus.
  Electrons are constantly moving, very fast.
• This kinetic energy overcomes the positive
  attraction of the nucleus.

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• 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.
  
  
  
  
  
  
  
  
  
  
  
  
  

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• 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.

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• Q Where does ionization energy come from?
• A Electricity

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• 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.

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• Q Why does ionization energy increase going
  across a period? Why, oh Why?!?
• A The effective nuclear charge DOES change on
  each valence electron!

ENC2
ENC1
11
12
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Mid-term

• Tuesday, April 22
• 1440-1610
• 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