chemical foundations for cells chapter 2. you are chemical, and so is every living and nonliving...
TRANSCRIPT
Chemical Foundations Chemical Foundations for Cellsfor Cells
Chapter 2Chapter 2
You are chemical, and You are chemical, and so so
is every living and is every living and nonliving thing in the nonliving thing in the
universe. universe.
ElementsElements
Fundamental forms of Fundamental forms of
mattermatter
• Can’t be broken apart by Can’t be broken apart by
normal meansnormal means 92 occur naturally on Earth92 occur naturally on Earth
Most Common Elements in Most Common Elements in Living OrganismsLiving Organisms
OxygenOxygen
HydrogenHydrogen
CarbonCarbon
NitrogenNitrogen
What Are Atoms?What Are Atoms?
Smallest particles that retain Smallest particles that retain
properties of an elementproperties of an element Made up of subatomic particles:Made up of subatomic particles:
Protons (+)Protons (+) Electrons (-) Electrons (-) Neutrons (no charge) Neutrons (no charge)
Atomic NumberAtomic Number
Number of protonsNumber of protons All atoms of an element have the All atoms of an element have the
same atomic numbersame atomic number Atomic number of hydrogen = 1Atomic number of hydrogen = 1 Atomic number of carbon = 6Atomic number of carbon = 6
Mass NumberMass Number
Number of protonsNumber of protons
++Number of neutronsNumber of neutrons
Isotopes vary in mass numberIsotopes vary in mass number
IsotopesIsotopes
Atoms of an element with different Atoms of an element with different numbers of neutrons (different mass numbers of neutrons (different mass numbers)numbers)
Carbon 12 has 6 protons, 6 neutronsCarbon 12 has 6 protons, 6 neutrons Carbon 14 has 6 protons, 8 neutronsCarbon 14 has 6 protons, 8 neutrons
What Determines What Determines whether Atoms Will whether Atoms Will
Interact?Interact?
The number and arrangement The number and arrangement of their electronsof their electrons
ElectronsElectrons
Carry a negative Carry a negative chargecharge
Repel one another Repel one another Are attracted to Are attracted to
protons in the nucleusprotons in the nucleus Move in orbitals - Move in orbitals -
volumes of space that volumes of space that surround the nucleussurround the nucleus
Z
X
When all p orbitals are full
y
Shell ModelShell Model
First shell First shell Lowest energyLowest energy Holds 1 orbital with up to 2 Holds 1 orbital with up to 2
electronselectrons
Second shellSecond shell 4 orbitals hold up to 8 4 orbitals hold up to 8
electronselectronsCALCIUM20p+ , 20e-
Electron VacanciesElectron Vacancies
Unfilled shells Unfilled shells make atoms make atoms likely to reactlikely to react
Hydrogen, Hydrogen, carbon, oxygen, carbon, oxygen, and nitrogen all and nitrogen all have vacancies in have vacancies in their outer shellstheir outer shells
CARBON6p+ , 6e-
NITROGEN7p+ , 7e-
HYDROGEN1p+ , 1e-
Chemical Bonds, Molecules, Chemical Bonds, Molecules, & Compounds& Compounds
Bond is union between electron Bond is union between electron structures of atomsstructures of atoms
Atoms bond to form moleculesAtoms bond to form molecules Molecules may contain atoms of only Molecules may contain atoms of only
one element - Oone element - O22
Molecules of compounds contain Molecules of compounds contain more than one element - Hmore than one element - H22OO
Chemical BookkeepingChemical Bookkeeping
Use symbols for elements when Use symbols for elements when writing formulaswriting formulas
Formula for glucose is CFormula for glucose is C66HH1212OO66
6 carbons 6 carbons
12 hydrogens12 hydrogens
6 oxygens6 oxygens
Chemical BookkeepingChemical Bookkeeping
Chemical equation shows reactionChemical equation shows reaction
Reactants ---> ProductsReactants ---> Products
Equation for photosynthesis:Equation for photosynthesis:
6CO6CO22 + 6H + 6H22O ---> + CO ---> + C66HH1212OO12 12 + 6H+ 6H22OO
Important Bonds in Important Bonds in Biological MoleculesBiological Molecules
Ionic BondsIonic Bonds
Covalent BondsCovalent Bonds
Hydrogen BondsHydrogen Bonds
Ionic BondingIonic Bonding
One atom loses electrons, One atom loses electrons, becomes positively charged becomes positively charged ionion
Another atom gains these Another atom gains these electrons, becomes electrons, becomes negatively charged ionnegatively charged ion
Charge difference attracts Charge difference attracts the two ions to each otherthe two ions to each other
Formation of NaClFormation of NaCl
Sodium atom (Na) Sodium atom (Na) Outer shell has one electronOuter shell has one electron
Chlorine atom (Cl) Chlorine atom (Cl) Outer shell has seven electronsOuter shell has seven electrons
Na transfers electron to Cl, forming NaNa transfers electron to Cl, forming Na++ and Cland Cl--
Ions remain together as NaClIons remain together as NaCl
Covalent BondingCovalent Bonding
Atoms share a pair or pairs of Atoms share a pair or pairs of electrons to fill outermost shellelectrons to fill outermost shell
•Single covalent bond
•Double covalent bond
•Triple covalent bond
Molecular hydrogen
Polar or Nonpolar BondsPolar or Nonpolar Bonds
Nonpolar if atoms share Nonpolar if atoms share electrons equally electrons equally Hydrogen gas (H - H)Hydrogen gas (H - H)
Polar if electrons spend more Polar if electrons spend more time near nucleus with most time near nucleus with most protonsprotons Water Water Electrons more attracted to O Electrons more attracted to O
nucleus than to H nuclei nucleus than to H nuclei
Hydrogen BondingHydrogen Bonding
Atom in one polar covalent molecule is Atom in one polar covalent molecule is attracted to oppositely charged atom in attracted to oppositely charged atom in another such molecule or in same another such molecule or in same moleculemolecule
Water molecule
Ammonia molecule
Figure 2.11aPage 27
Hydrogen Bonding in DNAHydrogen Bonding in DNA
Figure 2.11dPage 27
Water Is a Polar Water Is a Polar Covalent MoleculeCovalent Molecule
Molecule has no net Molecule has no net chargecharge
Oxygen end has a Oxygen end has a slight negative chargeslight negative charge
Hydrogen end has a Hydrogen end has a slight positive chargeslight positive charge
H H
O
Figure 2.12aPage 28
Properties of WaterProperties of Water
Bonds to hydrophilic substances Bonds to hydrophilic substances Repels hydrophobic onesRepels hydrophobic ones Temperature stabilizingTemperature stabilizing Expands when it freezesExpands when it freezes CohesiveCohesive Capacity to dissolve substancesCapacity to dissolve substances
Liquid water Ice
Figure 2.12b,cPage 28
Hydrogen Ions: HHydrogen Ions: H++
Unbound protonsUnbound protons
Have important biological Have important biological
effectseffects
Form when water ionizesForm when water ionizes
The pH ScaleThe pH Scale
Measures HMeasures H++ concentration of fluid concentration of fluid Change of 1 on scale means 10X Change of 1 on scale means 10X
change in Hchange in H++ concentration concentration
Highest HHighest H++ Lowest H Lowest H++
0---------------------7-------------------140---------------------7-------------------14Acidic Neutral BasicAcidic Neutral Basic
Examples of pHExamples of pH
Pure water is neutral with pH of 7.0 Pure water is neutral with pH of 7.0 AcidicAcidic
Stomach acid: pH 1.0 - 3.0Stomach acid: pH 1.0 - 3.0 Lemon juice: pH 2.3Lemon juice: pH 2.3
BasicBasic Seawater: pH 7.8 - 8.3Seawater: pH 7.8 - 8.3 Baking soda: pH 9.0Baking soda: pH 9.0
Acids & BasesAcids & Bases
AcidsAcids Donate HDonate H++ when dissolved in water when dissolved in water
Acidic solutions have pH < 7Acidic solutions have pH < 7
BasesBases Accept HAccept H++ when dissolved in water when dissolved in water
Acidic solutions have pH > 7Acidic solutions have pH > 7
SaltsSalts
Compounds that release ions other Compounds that release ions other than Hthan H++ and OH and OH-- when dissolved in when dissolved in water water
Example: NaCl releases NaExample: NaCl releases Na++ and Cl and Cl––
Many salts dissolve into ions that Many salts dissolve into ions that play important biological roles play important biological roles