HNRS 227 Lecture 11 Chapter 8 and Chapter 9

The Periodic Table and Chemical Reactionspresented by Prof. Geller with materials from Prof. Taylor

Recall from Chapter 8History 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 (1

1H; 1 electron; stable ?) Helium (2

4He; 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 (10

20Ne)

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 (18

40Ar)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 shellRow 1 = 2Row 2 = 8Row 3 = 8Row 4 = 18etc

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 BondsChapter 9

Review valence electronsPrinciples of “Bonds Away”Ionic BondsMetallic BondsCovalent BondsIntermolecular ForcesCommon 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 electronsAccept electronsShare electrons

Ionic Bonds

Some atoms give away electrons whereas other atoms receive electrons

Example of lithium (Li) chloride (Cl)

36Li + 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 chlorideLi + 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 bondsKey: 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)1

1H 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 scaleAny increase in H+ results in more acid

solution from 7 to 0Any increase in OH- results in more basic

solution from 7 to 14Examples

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