vwt 272 class 4 - napa valley college lecture 4.… · vwt 272 class 4 quiz 3 number of quizzes...

VWT 272 Class 4

Quiz 3

Number of quizzes taken

Min 7

Max 30

Mean 22.7

Median 28

Mode 30

Week 4 The Molecule and Bonding

Once we understand how molecules are formed, we can manipulate them. If you can manipulate molecules, you can manipulate genes and matter, you can synthesize new material - the implications are just unbelievable.

Ahmed Zewali (1946 - ?)

Plan of Study

• Review of the Atom & the Periodic Table

• The Molecule

– Ionic Bonds

– Covalent Bonds

• Simple Chemical Structures

What We Learned About the (Bohr) Atom

• Atoms are the smallest unit of an element • Elements are different due to the mass of their atoms

– The mass is mostly in the nucleus – The nucleus is the home of positive and neutral particles

• Negatively charged electrons move around the nucleus in fixed orbits

• Atoms are have no charge so the number of electrons (-) and protons (+) are equal

• The chemical properties of each element is determined by the number of electrons in the outer orbits of its atoms

What We Learned About the (Bohr) Atom

The Shell Model of the (Bohr) Atom

The Orbital Shells

• Electrons

– Outside of the Nucleus

– Occupy discrete areas/energy levels - “shells”

• 4 types of shells (s, p, d, h)

– Negative charge (-)

– “Light” (5.486 x 10-4 u)

– Responsible for chemical bonding

– Can move between nuclei to form ions

• Ion is an atom that has more or fewer electrons than protons

The Ion

•Note that the LOSS of an negatively (-) charged electron makes the resulting ion positive (+) •Ions with a positive charge are called cations •Ions with a negative charge are called anions

“You Can’t Buy Ions!” a cation (+) can’t exist without an anion (-)

Modern Periodic Table So two months ago!

The Periodic Table • Horizontal Rows are called Periods

– Left to Right • Mass increases slowly

• Properties change – metals → metalloids → non-metals → Nobel gasses

• Vertical Columns are called Groups – Top to Bottom

• Mass increases rapidly

• Properties remain similar – Alkali Metals (Li, Na, K, etc.) – highly reactive – form 1+ ions

– Alkaline Earth Metals (Be, Mg, Ca, etc.) – very reactive – form 2+ ions

– Halogens (F, Cl, Br, etc.) – low boiling temperatures – form 1- ions

– Noble Gasses (He, Ne, Ar, etc.) – Very unreactive – form NO ions

Chemistry is the “Search for Nobility”

Chemistry is the “Search for Nobel-ity”

Chemistry is the “Search for Nobility”

Noble Gasses • Neon (Ne)

Noble Gasses • Argon (Ar)

The Octet Principle

• Gilbert Lewis (1875 - 1949)

– American

– “In chemical compounds, atoms tend to have the electron configuration of a noble gas.”

– Coined “The Rule of 8” • There are 8 valence electrons in

most atoms in chemical compounds

– Nominated 35 times for a Nobel Prize

The Octet Principal

• Noble Gasses have a “Full” outer shell

– 8 electrons in 4 pairs

• Except H and He which have an outer shell of 2 electrons

– Outer electrons called Valence Electrons

Lewis Dot Structure of Ne

Lewis Dot Structures

• More Lewis Dot Structures

“You Can’t Buy Ions!” a cation (+) can’t exist without an anion (-)

Opposites Attract

• Ionic Bonding

Na + Cl → Na+ + Cl- → NaCl

Opposites Attract

• Ionic Bonding

– Is a type of chemical bond that involves the electrostatic attraction between oppositely charged ions, and is the primary interaction occurring in ionic compounds. (Wikipedia)

Opposites Attract

• Ionic Bonding

Mg + Cl + Cl → Mg2++ Cl- + Cl- → MgClCl

Mg + 2Cl → Mg2++ 2Cl- → MgCl2

Opposites Attract

• Ionic Bonding Examples – Sodium bromide - NaBr

– Potassium Chloride – KCl

– Calcium Chloride – CaCl2

– Magnesium Oxide – MgO

• Metals to Nonmetals

Sharing is Caring

• Covalent Bonding

Cl + Cl → ClCl→ Cl2

Sharing is Caring

• Covalent Bonding Examples – Hydrogen Cloride – HCl

– Oxygen Dihydroxide – H20

– Methane - CH4

• Nonmetals to Nonmetals

Sharing is Caring

• Covalent Bonding Examples

H + Cl → HCl

Sharing is Caring


2H + O → H2O

Sharing is Caring


4H + C → CH4

The Worst Bond Movie Ever!

The Cutest Bond Movie Ever!

Polar Covalent Bonds

• Middle ground between Ionic and Covalent Bonds

Electronegativity

If the difference is between 0.0 and 0.4 → non-polar covalent bond If the difference is between 0.4 and 1.7 → polar covalent bond If the difference is > 1.7 → ionic bond

Pauling’s Teeter Totter


A B

If two atoms have equal electronegativity • both have the same desire to attract the bonding pair of electrons • electrons will be found on average half way between the atoms • Covalent Bond


Aδ+ Bδ-

If two atoms have slightly different electronegativity • one atom (B) will have more desire to attract the bonding pair of electrons • electrons will be found on average closer to the more electronegative atom • Polar Covalent Bond


A+ B-

If two atoms have highly different electronegativity • one atom (B) will have a lot more desire to attract the bonding pair of electrons • electrons will be found on average very close to the more electronegative atom • Ionic Bond

Electronegativity Increases Across a Period


Patterns of Electronegativity

• Factors that explain electronegativity

– The number of protons in the nucleus

• More positively charged protons – Na vs. Cl

» Na has 11 protons

» Cl has 17 protons

Electronegativity more protons - more better

11Na+ 17Cl-

Electronegativity Decreases Down a Group


Patterns of Electronegativity

• Factors that explain electronegativity

– The “shielding” by the electrons in closer shells

• More negatively charged electrons in the way – F vs. Cl

» F has 9 protons shielded by 2 electrons

» Cl has 17 protons shielded by 10 electrons

Electronegativity more electrons - more shielding

H+ Cl- H+

H+ F-

Polar Bonds and Polar Molecules

• Bar Magnet

– One end (pole) is attractive to positive charges

– Other end (pole) is attractive to negative charges

δ+ δ-

Polar Bonds and Polar Molecules J.J. Thompson - Movie Star!

The Atom & Dead White Men

• Joseph John Thomson (1856 – 1940)

– England

– Discovered the first sub-atomic particle, the Corpuscles (Electron) • About 1,840 times lighter than

Hydrogen

• Always the same

• Negatively charged

– Won the Nobel Prize 1906

Polar Bonds and Polar Molecules J.J. Thompson - Movie Star!


– Cl2

– Cl has an electronegativity of 3.0

– Cl has an electronegativity of 3.0 • So bond is Non-Polar Covalent

– Electrons and charge are equally distributed around the molecule

– Molecule is Nonpolar


• Carbon Tetrachloride

– CCl4


– C has an electronegativity of 2.5

• So bonds are Polar Covalent

– Partial charge is equally distributed around the molecule

– Molecule is Nonpolar


• Chloroform

– CHCl3


– C has an electronegativity of 2.5

– H has an electronegativity of 2.1

• So all bonds are Polar Covalent

– Partial charge is NOT equally distributed around the molecule

– Molecule is Polar

Polar Bonds and Polar Molecules Carbon Tetrachloride vs. Chloroform

δ+

δ-

Water – a Polar Covalent Molecule

Drawing a Single Bond

H2

Bond, Single Bonds

• Ethanol

• Octane

Sharing is Caring x2 & x3 Double and Triple Bonds

Carbon Dioxide • CO2

– One Carbon

• 4 valence electrons

– Two Oxygen

• 6 valence electrons

– Total valence electrons

• 4 + (6 x 2) = 16

Hydrogen Cyanide • HCN

• One Carbon – 4 valence electrons

• One Hydrogen – 1 valence electron Ḣ

• One Nitrogen – 5 valence electrons

• Total valence electrons – 4 + 1 + 5 = 10

Bond Length

Compound Simple

Formula Name Bond Order

Bond Length (pm)

Bond Dissociation

Energy (kJ/mol)

H3C–CH3 C2H6 Ethane 1 153.5 376

H2C=CH2 C2H4 Ethylene 2 133.9 728

HC≡CH C2H2 Acetylene 3 120.3 965

Methanol - 6 Ways

Our New BFF, Carbon

Propane - 4 Ways

Bond, Single Bonds The Sequel

• Ethanol

• Octane

Some Molecules in Wine

Ethanol (C2H6O or C2H5OH )

Glucose (C6H12O6)

Next Week

• More Chemical Nomenclature

• Introduction to Acids and Bases

– pH and TA

vwt 272 class 4 - napa valley college lecture 4.… · vwt 272 class 4 quiz 3 number of quizzes...

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