Bonding

Neutral Atoms (as seen on the periodic table)

• 39 Mass Number p + nK

• 19 Atomic Number p

• (electrons = number of protons)

• (negative charges = positive )

Atomic Structure

• Click Here

Animation Periodic Table

Isotope• Atoms that differ in number of

neutrons

• Also differ in mass number (since it is p+n)

• 41 Note more nK

• 19 Note same p

Ion• Charged atom

• Differs in number of electrons

• 39 Same mass number

K+ means lost one electron

• 19 Same atomic number

ION

• Charged atom

• Na+ (has lost one electron)

• O-2 (has gained two electrons)

Bonding

• Covalent

• share electrons

• Ionic

• transfer of electrons

• (lose or gain)

IONIC BOND

• An atom may lose one or more electrons and become positive (+)

• An atom may gain one or more electrons and become negative (-)

• The (+) and (-) ions formed now attract each other and form an ionic bond.

Ionic Bonds

• Sodium loses Chlorine gains

• an electron an electron

• become + becomes -

NaCl: Ionic Bond

Tutorial 2.1 Chemical Bond Formation

Why do atoms bond?

•To have filled outer electron shells!

•Atom Heaven

•(stable)

Why do atoms bond?

•See the filled electron shells.

Filled outer e- shells

How many e- fill the first shell (nearest the nucleus)?How many e- fill the next two shells?2,8,8

nucleus

Gain 1 e- or lose 7 e-?

If gains 1 e-, then it becomes -1

Gain 7 e- or lose 1 e-?

If loses 1 e-, the it becomes +1.

Gain or Lose ?

If it could as easily lose or gain e-, then it will probably share them. It will form a covalent bond.

Covalent Bonding = Shared e-

Polar Covalent Bonding of Water:Unequal sharing of electrons

Covalent BondsClick HERE: Chemical Bonding

•Electrons are shared

•Usually if near the same number of e- in outer shells

Nonpolar Covalent Bond

• Equal sharing of electrons

• Like with carbon dioxide

Bonds

• Single Bond C-C C:C

• Double Bond C=C C::C

• Triple Bond C≡C C:::C

Single Bond and Double Bonds

Chemical Reaction

• A process to break or share electrons to form or break bonds

• Click Here Sodium and Chlorine Chemical Reaction

• Also scroll down for covalent bonding

• AND polar covalent bonding in water

Chemical Reactions

• Reactants on the left of the arrow

• Products on the right of the arrow

• IDENTIFY:

• 2Mg(s)  +  O2(g)  →    2MgO(s)

• MgO(s)  +   H2O(l)  →    Mg(OH)2(s)

• N2(g)  +  3H2(g)  →    2NH3(g)

Chemical Reaction Example

• A silver spoon tarnishes. The silver reacts with sulfur in the air to make silver sulfide, the black material we call tarnish.

2 Ag + S Ag2S

Chemical Reaction Example

• An iron bar rusts. The iron reacts with oxygen in the air to make rust.

4 Fe + 3 O2 2 Fe2O3

WATER

• Polar Covalent Bonds

H

H

O

Polarity of Water

• Uneven sharing of electrons

• Polar covalent

• Polar Bonding

Contrast

• Polar• Uneven distribution of

electrons• EX: Water•

• Non-polar• Even distribution of

electrons

• EX: CO, oil

Hydrogen Bonds

• O - to H+

• to 4 other water

Hydrogen Bonds

• Between slightly (+) H atom to a slightly (-) atom of a different molecule

• H-bonding of Water (nice animation)

Hydrogen Bonds

• Weak bonds

• But they are strong enough to cause water to needing a lot of heat to boil or to evaporate, and they form a less dense ice open lattice.

Cohesion

• Water is attracted to other water molecules (similar polar molecules)

• H-bonding between water molecules hold them together

Cohesion is why a waterfall, a stream, a water drop forms

Adhesion

• Attraction of unlike substances

• Like water to the sides of a glass tube

Not so much with plastic

Strong adhesion to glass

Water is a Good Solvent

• Can dissolve many substances

Water is the “Universal Solvent”

• Dissolving NaCl in water movie

• dissolve

Water is the Universal Solvent

• WHY? Can dissolve a lot of things

• What types of compounds are good at dissolving?–Polar–Ionic

How does detergent work?Soap has a water-loving (hydrophilic) and a water-hating end (hydrophobic).

It attaches to the oil and then the water to wash away the oil.

Amphipathic

• Bipolar

• A molecule that is water-loving (polar) at one end and water-hating (non-polar, like oils) at the other end

Capillary Action

• The thinner the straw or tube the higher up capillary action will pull the water.

• Plant Capillarity

High Specific Heat• Takes a lot of heat to raise the

temperature of water (break the H-bonds)

• This is why coastal areas have mild climates

Surface Tension

-the attraction of molecules to each other on a liquid's surface --creates a “film”Surface Tension

Floating Penny

• And paper clip

H-bonds pull in water molecules and form a “film”

Water Strider

• Can stand on top of water

• Basilisk Lizard on Water

• Water strider skimming across pond

Can exist as...

• Gas Liquid Solid

• Note in the solid ice, it is not much denser

• Due to H-bonds opening a lattice

High Heat of Vaporization

• Takes a high temperature to evaporate, or boil water

• Need to break those

H-bonds

High Heat of Fusion

• Takes a low temperature to freeze water

• Those H-bonds must form

Water expands upon freezing

• If water worked like other liquids, then there would be no such thing as an ice berg, the ice cubes in your soft drink would sink to the bottom of the glass, and ponds would freeze from the bottom up!

Ice forms an Open lattice

• Below 4oC

• Ice floats

• H-bonds are more stable in the solid form of water

Ice Expands

Water Molecules

• Can bond to four other water molecules

• H+ end attracts the O-ends

• + +

• -

Solutions

• A SOLUTE is the substance to be dissolved (sugar). The other is a SOLVENT. The solvent is the one doing the dissolving (water). As a rule of thumb there is usually more solvent than solute.

Solution = solvent + solute

SOLUTIONS

• When one substance dissolves another substance.

• SOLVENT + SOLUTE = SOLUTION• Solvent=material in which the other

material is being dissolved• Solute=what is being dissolved

SALT SOLUTION

• Animation of Salt Dissolving in Water

• Dissolve Another Nice Animation

• When water is the solvent, the solution is called an aqueous solution.

Salt Solution

Which is the solvent?

Which is the solute?

Water is solvent. Salt is the solute.

FYI

• The solvent is defined as the substance that exists in a greater quantity than the solute(s) in the solution.

• Generally polar or ionic compounds will only dissolve in polar solvents.

Can you undissolve a dye?

• Undeniable Facts: Undeniable Friday: Un-dissolving Dye- a fact a day

• Scroll down web page for explanation.

Dissociation (break into its ions) of Water

• Acids release H+ (hydronium)

• Bases release OH- (hydroxide)

Hydronium Ion = H+ Hydroxide Ion = OH-

Animation of Dissociation of Water

pH

• * at pH 7.0, a solution is neutral

• * at lower pH (1-6), a solution is aacidic

• * at higher pH (8-14), a solution is basic

How much more?

• For every pH level lower there are 10 X’s more H+ ions

• So…… pH 2 has how many more H+ ions than pH 3?

• 10• So…pH 2 has how many more H+ ions

than pH 4?• 100

pH

• 1-6 = acid (the closer to “1” the stronger the acid) donates lots of H+ ions

• 8-14 = base (the closer to “14” the stronger the base) donate lots of OH- ions

• 7 = neutral or equal number of H+ and OH-

Buffer

• A substance that resists a change in pH when small quantities of acid or base are added

• (they are in the pH solutions for the duckweed)

Buffer

• A substance that resists a change in pH when small quantities of acid or base are added

• (they are in the pH solutions for the duckweed)

Buffer Animation

• Buffer Animation with narration (click here)