Chapter 2 - ChemistryChapter 2 - Chemistry

All Matter is Composed of All Matter is Composed of AtomsAtoms

ElectronsElectrons

ProtonsProtons

NeutronsNeutrons

Atoms have Volume and MassAtoms have Volume and Mass

Mass of one protonMass of one proton

or one neutron = 1 or one neutron = 1 dalton (Da)dalton (Da)

Mass of one electron = 9 Mass of one electron = 9 ×× 10 10––2828

((usually ignored).usually ignored).

ElementsElements

Element: pure substance containing only Element: pure substance containing only one kind of atom.one kind of atom.

Elements are arranged in the Elements are arranged in the periodic periodic table.table.

Each element has a unique chemical Each element has a unique chemical symbol.symbol.

The Periodic Table The Periodic Table

Periodic TablePeriodic Table

The Periodic Table The Periodic Table 98 % of living organisms are made up of C, H, N, O, S, P

IsotopesIsotopesSome isotopes are unstable:

Radioisotopes give off energy in the form of alpha, beta, and gamma radiation from the nucleus.

ElectronsElectrons

The number of electrons determines how The number of electrons determines how atoms will interact.atoms will interact.

Chemical reactions involve changes in Chemical reactions involve changes in the distribution of electrons between the distribution of electrons between atoms.atoms.

Orbital TheoryOrbital TheoryLocations of electrons in Locations of electrons in an atom are described by an atom are described by orbitals. orbitals.

Orbital: region where Orbital: region where electron is found at least electron is found at least 90% of the time.90% of the time.

Orbitals have Orbitals have characteristic shapes and characteristic shapes and orientations, and can be orientations, and can be occupied by two occupied by two electrons.electrons.

Orbitals are filled in a Orbitals are filled in a specific sequence.specific sequence.

Orbital TheoryOrbital TheoryOrbitals occur in a series called electron shells or Orbitals occur in a series called electron shells or energy levelsenergy levels..

First shellFirst shell: one : one ss orbital (holds 2 electrons) orbital (holds 2 electrons)

Second shellSecond shell: 1 : 1 ss and 3 and 3 pp orbitals (holds 8 electrons) orbitals (holds 8 electrons)

Additional shells: 4 orbitals (8 electrons)Additional shells: 4 orbitals (8 electrons)

Octet Rule!Octet Rule!

So how does Orbital Theory work?So how does Orbital Theory work?

Fill electrons from the inside out.Fill electrons from the inside out.

The outermost energy shell is called theThe outermost energy shell is called the

Valence Shell Valence Shell

How Do Atoms Bond to Form How Do Atoms Bond to Form Molecules?Molecules?

Chemical bond: attractive force that Chemical bond: attractive force that links atoms together to form links atoms together to form molecules.molecules.

Valence shells of each atom interactValence shells of each atom interact

Covalent BondsCovalent BondsAtoms Atoms shareshare one or more one or more pairs of pairs of electrons, so electrons, so that the outer that the outer shells are filled.shells are filled.

Strongest BondsStrongest Bonds(takes a lot of energy to (takes a lot of energy to

break)break)

CompoundCompound: a : a molecule made up of molecule made up of two or more elements two or more elements bonded together in a bonded together in a fixed ratio.fixed ratio.

The molecular weightThe molecular weight of a compound is the of a compound is the sum of the atomic sum of the atomic weights of all atoms in weights of all atoms in the molecule.the molecule.

ElementElement Usual # of Usual # of Covalent BondsCovalent Bonds

Hydrogen (H)Hydrogen (H) 11

Oxygen (O)Oxygen (O) 22

Sulfur (S)Sulfur (S) 22

Nitrogen (N)Nitrogen (N) 33

Carbon (C)Carbon (C) 44

Phosphorus (P)Phosphorus (P) 55

Types of Covalent BondsTypes of Covalent Bonds

Covalent bonds can beCovalent bonds can be

• SingleSingle—sharing 1 pair of electrons —sharing 1 pair of electrons

• DDoubleouble——sharing 2 pairs of electronssharing 2 pairs of electrons

• TripleTriple——sharing 3 pairs of electrons sharing 3 pairs of electrons

ElectronegativityElectronegativity

Sharing of electrons in a covalent bond Sharing of electrons in a covalent bond is not always equal.is not always equal.

Electronegativity:Electronegativity: the attractive force the attractive force that an atomic nucleus exerts on that an atomic nucleus exerts on electrons.electrons.

ElementElement ElectronegativityElectronegativity

Oxygen (O)Oxygen (O) 3.53.5

Chlorine (Cl)Chlorine (Cl) 3.13.1

Nitrogen (N)Nitrogen (N) 3.03.0

Carbon (C)Carbon (C) 2.52.5

Phosphorus (P)Phosphorus (P) 2.12.1

Hydrogen (H)Hydrogen (H) 2.12.1

Sodium (Na)Sodium (Na) 0.90.9

Potassium (K)Potassium (K) 0.80.8

Electronegativity Video

Polar / Non-polar Covalent BondsPolar / Non-polar Covalent Bonds

• A A polar covalent bondpolar covalent bond results when results when electrons are drawn to one nucleus more electrons are drawn to one nucleus more than to the other, because one atom has than to the other, because one atom has more electronegativitymore electronegativity

What type ofWhat type of

polar polar

moleculemolecule

Is this?Is this?

• What about a What about a non-polar covalent bondnon-polar covalent bond??

Ionic BondsIonic Bonds

When one atom is much more electronegative When one atom is much more electronegative than the other, a complete transfer of electrons than the other, a complete transfer of electrons may occur.may occur.

This results in two This results in two ionsions with fully paired with fully paired electrons in their outer shells. electrons in their outer shells. (Not an ionic bond!) (Not an ionic bond!)

Ionic BondsIonic Bonds

• The charged The charged ions ions the interact to form the interact to form an ionic bondan ionic bond

• Opposites attract…Opposites attract…

IonsIons

IonsIons: electrically charged particles— when : electrically charged particles— when atoms lose or gain electronsatoms lose or gain electrons

CationsCations—positive—positive

AnionsAnions—negative —negative

Ionic bondsIonic bonds are formed by the electrical are formed by the electrical attraction of positive and negative ions.attraction of positive and negative ions.

SaltsSalts are ionically bonded compounds. are ionically bonded compounds.

Water is a polar compound Water is a polar compound which can dissolve a saltwhich can dissolve a salt

Hydrogen BondsHydrogen Bonds

Hydrogen bondsHydrogen bonds::

attraction betweenattraction between

the the δδ–– end of end of oneone

molecule and the molecule and the δδ++

hydrogen end ofhydrogen end of

another molecule.another molecule.

Water/DNA/ProteinsWater/DNA/Proteins

Hydrophobic InteractionsHydrophobic Interactions

Polar molecules that form Polar molecules that form hydrogen bonds with water hydrogen bonds with water are are hydrophylichydrophylic (“water- (“water-loving”).loving”).

Nonpolar molecules such Nonpolar molecules such as hydrocarbons that as hydrocarbons that interact with each other, but interact with each other, but not with water, are not with water, are hydrophobichydrophobic

(“water-hating”).(“water-hating”).

van der Waals forcesvan der Waals forces

van der Waals forcesvan der Waals forces: attractions between : attractions between nonpolar molecules that are close nonpolar molecules that are close together. together.

Individual interactions are brief and weak, Individual interactions are brief and weak, but summed over a large molecule, can be but summed over a large molecule, can be substantial.substantial.

Chemical ReactionsChemical Reactions

Occur when atoms collide with enough Occur when atoms collide with enough energy to combine or change their energy to combine or change their bonding partners.bonding partners.

Water has a unique structure which Water has a unique structure which allows it to have “Special Properties”allows it to have “Special Properties”

- Polar molecule- Polar molecule

- Forms hydrogen bonds- Forms hydrogen bonds

- Tetrahedral shape- Tetrahedral shape

Phase Shift of WaterPhase Shift of Water

• Latent HeatLatent Heat – heat – heat given off or given off or absorbed during absorbed during phase changephase change

www.piercecollege.com/offices/weather/water.html

Special Properties of Water: Special Properties of Water: Ice FloatsIce Floats

– Less DenseLess Dense– Most Stable Most Stable

(lower energy state)(lower energy state)

EnvironmentalEnvironmental

Significant?Significant?• Oceans Oceans • HorticultureHorticulture

Special Properties of Water: Special Properties of Water: Heat CapacityHeat Capacity

Heat Storage Heat Storage

Water has Water has high specific high specific heat:heat:

the amount of heat the amount of heat energy required to energy required to raise the temperature raise the temperature of 1 gram of water by of 1 gram of water by 11°°C.C.

Environmental Environmental Significance?Significance?

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Special Properties of Water:Special Properties of Water:Evaporational CoolingEvaporational Cooling

Heat of Vaporization (Latent)Heat of Vaporization (Latent)• Uses Energy to break H-bondsUses Energy to break H-bonds

• Energy is absorbed during the transition from Energy is absorbed during the transition from liquid to water vaporliquid to water vapor

Environmental Significance?Environmental Significance?

Special Properties of Water:Special Properties of Water:CohesionCohesion

In liquid 3.4 H-In liquid 3.4 H-bonds at all timesbonds at all times

Environmental Environmental SignificanceSignificance

– Surface TensionSurface Tension– TranspirationTranspiration

Aqueous SolutionsAqueous Solutions

A A solutionsolution is a substance ( is a substance (solutesolute))

dissolved in a liquid (dissolved in a liquid (solventsolvent).).

Acids/BasesAcids/Bases

BuffersBuffers

Acids and BasesAcids and Bases

AcidsAcids: dissolve in water : dissolve in water and release hydrogen and release hydrogen ions: Hions: H+ + (protons).(protons).

\\ BasesBases: accept H: accept H++ ions. ions.

ClHHCl

HCOOHCOOH

OHNaNaOH

OHHOH 2

323 COHHHCO

Strong Acid

Weak Acid

Strong Base

Weak BaseReduces H+

Is water an acid or a base?Is water an acid or a base?

• Water acts as Water acts as bothboth a weak acid and a a weak acid and a weak base.weak base.

• Water has a slight tendency to ionize.Water has a slight tendency to ionize.

OHHOH 2

pHpHpH = negative log of the pH = negative log of the molar concentration of Hmolar concentration of H+ +

ions.ions.

HH++ concentration of concentration of purewater is 10purewater is 10––77 M M pH = 7.pH = 7.

1010––77 [H [H++] + ] + 1010––77 [OH [OH--] ] == 10 10––1414

Lower pH numbers mean Lower pH numbers mean higher Hhigher H++ concentration, or concentration, or greater acidity.greater acidity.

HpH log

pH QuestionspH Questions

• If the pH of a If the pH of a solution was 2.solution was 2.– [ H[ H++]=?]=?– [OH[OH--]=?]=?

• If a solution has a If a solution has a [ H[ H++]=10]=10-5-5

– pH=?pH=?– [OH[OH--]=?]=?

BuffersBuffersLiving organisms Living organisms maintain constant internal maintain constant internal conditions (conditions (homeostasishomeostasis).).

Buffers help maintain Buffers help maintain constant pH.constant pH.

A buffer is a weak acid A buffer is a weak acid and its corresponding and its corresponding base.base.

323 COHHHCO