Transcript HNRS 227 Lecture 11 Chapter 8 and Chapter 9

HNRS 227 Lecture 11
Chapter 8 and Chapter 9
The Periodic Table and Chemical Reactions
presented by Prof. Geller with materials
from Prof. Taylor
Recall from Chapter 8
History of atomic theory
Electron and nucleus (protons and neutrons in
nucleus both made up of quarks)
The Bohr Model of the Atom
The Quantum Concept
Bohr’s Theory
Quantum Mechanics
Quantum numbers
Principal, angular momentum, magnetic, and spin
Electron Configuration
Pauli Exclusion Principle
Filling of orbital shells
Periodic Table of Elements
An underlying principle
most stable state for an atom is one in which
the outermost shell is filled with the maximum
number of electrons
1st Shell (1 orbit; 2 electrons)
Hydrogen (11H; 1 electron; stable ?)
Helium (24He; 2 electrons; stable ?)
Periodic Table’s 1st Row
Hydrogen and Helium
Periodic Table of Elements
2nd shell has 4 orbits with 2 electrons
(maximum) per orbit (total of 8
electrons/shell)
Most stable configuration is the following:
1st shell filled with 2 electrons
2nd shell filled with 8 electrons
Total of 10 electrons (1020Ne)
2nd row of Periodic Table
8 elements (list and relate to the above)
Periodic Table of Elements
3nd shell has 4 orbits with 2 electrons
maximum per orbit (total of 8
electrons/shell)
Most stable configuration is the following:
1st shell filled with 2 electrons
2nd shell filled with 8 electrons
3rd shell filled with 8 electrons
Total of ___ electrons (1840Ar)
3nd row of Periodic Table
8 elements (list and relate to the above)
Periodic Table of Elements
Rows
Number of elements in a row is not chance
but reflects the maximum number of electrons
in the outermost shell
Row
Row
Row
Row
etc
1
2
3
4
=
=
=
=
2
8
8
18
Periodic Table of Elements
Columns
Elements in a given column have similar
chemical properties
All elements in column have the same number
of valence electrons
Column IA has 1 electron in outer shell
Column IIA has 2 electrons in outer shell
Column IIIA has 3 electrons in outer shell
Column IVA has 4 electrons in outer shell
Column VA has 5 electrons in outer shell
Periodic Table of Elements
Taylor’s Take Home Message
 Atoms are the chemical building blocks of all matter
 Structure of atoms (electrons, neutrons, protons and
their arrangement) determine the unique
behavior/attributes of the elements
 Of the above (No. 2), the “place” and “pairing” of the
electrons are the most critical in chemical reactions
 Electrons reside in defined shells (orbits) surrounding the
nucleus of the atom and the electrons in the outermost
shell (valence electrons) determine an atom’s chemical
reactivity
 Utility and periodicity of the Periodic Table of Elements is
a function of the distribution of all electrons in shells, the
valence electrons in the outermost shell, and the mass of
the element
Chemical Reactions and Bonds
Chapter 9
Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions
Taylor’s Take Home Message
 When atoms combine to produce molecules and
compounds, expect the chemical properties of the
molecules/compounds to be far different than that of the
constituent atoms (hierarchy theory)
 Atoms bind together by re-arranging and sharing
electrons
Ionic bonds
Metallic bonds
Covalent Bonds
Intermolecular forces (e.g., hydrogen bond)
 Chemical interactions make and break bonds between
atoms and in so doing effect a change in energy
(potential and kinetic)
 Weak chemical bonds (e.g., covalent bonds) play a very
important role in the chemistry of life
Chapter Items that won’t be
emphasized from Chapter 9
p. 184
A Closer look
p. 186
A Closer Look
pp. 188-191
Percent Composition of Compounds
Ion Exchange Reactions
Atoms in Proximity:
Chemical Bonds
Chemical Action
when two atoms are brought together,
electrons will tend to re-arrange themselves to
the lowest energy state where the valence
electrons are most stable
Chemical Reaction
electrons are re-arranged into bonds
Give away electrons
Accept electrons
Share electrons
Ionic Bonds
Some atoms give away electrons
whereas other atoms receive
electrons
Example of lithium (Li) chloride (Cl)
3 Li
6
+
17
35.5Cl
= LiCl
Ionic Bonding
Lithium (Li)
Li gives up 1 electron and is left with 2 electrons (-) and 3 protons (+); net
positive (+) charge
Chlorine (Cl)
Cl has 1 unpaired electron in valence shell, so Cl tends to accept an electron
and is left with 18 electrons (-) and 17 protons; net negative (-) charge
Ionic Bonding Summary
 Some atoms give away electrons while other atoms
receive electrons
 Example of lithium chloride
Li + Cl = LiCl
 Bonding via electrical attraction between Li+ and ClLi+ + Cl - = Li+Cl-
 Consequence: ionic bonds are underpinned by charged
ions and tend to form crystals of very specific and
repeating geometry (very rigid)
 Example: NaCl is based on ionic bonds and is salt
Ionic Bond Example: Salt
Metallic Bonds
Some elements do not give or take electrons
(ionic bonds) BUT share electrons
Valence electrons tend to move freely between
both atoms (contrast with ionic bonds)
Significance of sharing electrons: compounds
tend to show two features
Malleability (easily worked or pounded)
Conductive of electricity (good conductors)
Examples
Gold jewelry
Copper wire
Covalent Bonds
Extremes of behavior in bonding
Accept or give away electrons (ionic bonds)
No tendency to share (noble gases)
Intermediate between these two extremes but
Do not form ionic bonds
Do not form metallic bonds
Yet share 1, 2, 3 and 4 electrons in unique
arrangement called covalent bonds
Key: orbits of valence electrons are shared so that electrons
are shared (and move) between valence shells of adjacent
atoms
Covalent Bond Example
Example of hydrogen fluoride (HF)
11H and 919F
Note: Valence shell for both atoms are full
Single bond shared
Double bond
Covalent Bonds with Carbon
 612C is a special case (profoundly important)
 Valence electrons for C are 4 (1 in each orbit) and
intermediate between giving and accepting
 C - C single covalent bond (1 orbit)
C
 C - C two covalent bonds involving 2 orbits
 Unique behavior of C
C
C-C-C
(or H or N or __)
C
Behavior of Valence Electrons
Five Options
No action (e.g., inert gases)
Give away one or more electrons in valence
state (positive ion leading to ionic bond)
Accept one or more electrons to valence state
(negative ion leading to ionic bond)
Share an electron with many other atoms
without respect to an orbit (metallic bond)
Share one or more electrons plus their orbits
with another atom (covalent bond)
Regarding Next Week’s Lab:
Evaporation and Chemical Structure
Vaporization and chemical properties of
molecules
Liquid to gas state change
State change has energy cost: endothermic
(temperature decrease)
Temperature change is a function of
chemical structure of molecule
Bonding and polarity
Evaporation and Chemical Structure
Organic compounds
Carbon based or hydrocarbons bond with other
elements via covalent bonds)
Alkanes: C and H only
• Pentane (C5H12)
Alcohols: C, H and OH (hydroxyl group)
• Ethanol (C2H5OH)
• Structural formula
Hydrogen bonding: H bonded to N, O or F (tight
bond)
Process: as chemical vaporizes, temperature
change is chemical specific and is a “window”
onto the chemical structure of molecule
Evaporation and Chemical Structure
Hypothesis
temperature changes with vaporization in a
manner that is predictable, based on the
bonding among atoms involving C, H and OH
Method
Measure temperature change electronically
Record for 6 hydrocarbons
Analyze data (graphically) based on
understanding of the bonds for each molecule
Intermolecular Forces:
Polarization & Hydrogen Bonding
 Example of water (H2O)
+H
H+
O When one molecule’s distribution of atoms results in one
side of the molecule having either a + or – charge
 Resulting distribution of charges causes adjoining H2O
molecule to align itself with + and – charges to be most
stable
 Called “polarity” of molecule (e.g., magnet)
 Relate to lab exercise: greater polarity, greater bonding
and less evaporation (less temperature change)
Intermolecular Forces: Van
der Waal Forces
In polarity, specific and rigid + and – fields on
each molecule that does not change over time
When molecules converge, inevitable that
electrons shift and re-distribute (e.g., planar
compound)
In re-distribution, small net attraction between
molecules arise and two molecules for weak
bond
Graphite pencil lead
Stack of paper
Acid – Base Reaction:
Measurement
pH scale
Any increase in H+ results in more acid solution
from 7 to 0
Any increase in OH- results in more basic
solution from 7 to 14
Examples
Rainwater of 5.6 means what?
Cell pH value of 6-8 means what?
Importance to biological systems and buffering
Taylor’s Take Home Message
 When atoms combine to produce molecules and
compounds, expect the chemical properties of the
molecules/compounds to be far different than that of the
constituent atoms (hierarchy theory)
 Atoms bind together by re-arranging and sharing their
electrons
Ionic bonds
Metallic bonds
Covalent Bonds
Intermolecular forces (e.g., hydrogen bond)
 Chemical interactions make and break bonds between
atoms and in so doing effect a change in energy
(potential and kinetic)
 Weak chemical bonds (e.g., covalent bonds) play a very
important role in the chemistry of life