chapter 2 the chemical context of life. chemistry definition –study of matter and its...
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Chapter 2
The Chemical Context of Life
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Chemistry
• Definition– Study of matter and its
transformations
• Matter– Has mass and
occupies space
• Transformations– Chemical reactions– Break or form
chemical bonds
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Units of Matter
• Element– Substance that cannot be
broken down further by chemical means
• Compound– Substance composed of
more than one element
• Molecule– Substance composed of
more than one atom– Includes diatomic elements
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Elements found in Living Organisms
• 98 % of living mass composed of 4 elements– Oxygen– Carbon– Hydrogen– Nitrogen
• Minerals• Trace elements
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The AtomBasic Unit of Elements
• Most fundamental unit of an element that retains the properties of the element
• Structure determines properties of element
• Composed of sub atomic particles
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Subatomic Particles
• Proton• Neutron• Electron
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Protons
• Composed of quarks– 2 ups and a down– http://en.wikipedia.org/wiki/
Quark
• Positive charge of +1• Mass of 1 AMU or Dalton• Resides in atomic
nucleus• Confers identity• Atomic number
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Neutrons
• Composed of quarks– 2 downs and an up
• Electrically neutral• Mass of 1 AMU• Resides in atomic
nucleus• Stabilizes atomic nucleus• Contributes to atomic
mass• Number varies• Isotopes
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Quarks and Leptonsboth Fermions
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Isotopes
• Forms of an element that differ in the number of neutrons
• Atomic mass changes but atomic number does not
• May be radioactive if atomic nucleus is over crowded
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Isotopes
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Common Radioactive Isotopes
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Types of Radioactive emissions
• Alpha – Helium nucleus– 2protons, 2 neutrons
• Beta– Electron equivalent– Neutron converts to
proton
• Gamma– EM radiation– Accompanies other
particles
G-
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Electrons
• Fundamental particle called a lepton http://en.wikipedia.org/wiki/Lepton
• Electrical charge of -1
• Mass negligible(1⁄1836 of that of the proton)
• Located outside the atomic nucleus in the electron cloud
• Neutralizes the charge of the protons
• Participates in chemical bonding
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Electron location within the Electron Cloud
• Distance from atomic nucleus indicates electron energy level
• The farther from the nucleus, the higher the energy
• Levels called shells (1st quantum number,N)
• Named as numbers (1,2,3…)• Maximum number of electrons
in each shell= 2N2
• Outer shell=valence shell• Outer shell electrons most
readily available for chemical bonding
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Electron location within the Electron Cloud
• Orbitals (2nd quantum number (l)
• Specific region in which an electron is likely to be found
• Named with letters– s- sharp– p-principal– d- diffuse– f-fundamental– Named after groups of
lines in the spectra of alkali metals
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Electron location within the Electron Cloud
• Shapes of orbitals• s spherical- 2 electrons• p party balloons- 6 e-
• d complex 10 e-
• f complex 14 e-
• Energy increases from s-f• Electrons usually fill from
s→f with some exceptions
• 3rd quantum number is the axis or magnetic orientation of the orbital (m)
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Electron Fill
• Electron configuration of an element
• Fill from lowest energy to highest energy location
• Opposite spins for electrons in same orbital (Pauli exclusion principle)
• Spin is the 4th quantum number (s)
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Sub Atomic Particles
Proton Neutron Electron
Mass (kg) 1.6726231x10-27
1.6749286x10-27
9.1093897x10-31
Charge [C] +1.602 0.0 - 1.602
Radius 8x10-16 8x10-16 less than 10-16
Composition
uud ddu N/A
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Periodic table
• Periods– Horizontal rows– Represent electron
filling of a shell– Fill from left to right– s 1st 2 groups– d transition metal– p right block,
metaloids, non metals– f lanthides and
actinides
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Electron configurations
• C
• N
• O
• Li
• Cl
• F
• Ne
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Bohr Model
• C
• N
• O
• Li
• Cl
• F
• Ne
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Chemical bonding
• Forms by interactions between valence shell electrons
• Goal- full valence shell• Two main types
– Ionic– Covalent
• Type determined by electro negativity differential
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Ionic Bonds
• Electron transfer• Large electro negativity
differential• Between metals and non
metals• Ions formed
– Cation– Anion
• Attraction between oppositely charged ions
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Covalent Bonds
• Electrons shared between atoms
• Low electro negativity differential
• Hybrid orbitals• Electron timeshare• Single• Double• Triple
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Polar Covalent Bonds
• Electrons not shared equally
• Creates a dipole• Rotates in electrical
field• Fosters dipole
interactions
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Non-Polar Covalent Bonds
• No separation of charges
• Equal electron sharing
• Even distribution of charges
• Fosters induced dipole interactions
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Dipole Interactions
• Occur between polar covalent molecules
• Stronger than interactions between non-polar molecules
• Slightly negative region of one molecule is attracted to slightly positive region of a neighboring molecule
• Cohesive
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Hydrogen Bonds
• Special type of dipole interaction
• Involves H as the slightly + component
• Very significant in biological systems– 2 strands of DNA– Protein shape– Genetic code
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Induced Dipole Interactions
• May be referred to as Van der Waals interactions
• Very weak
• Between non-polar covalent molecules
• Volatility of non-polars compared to polars
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Induced Dipole Interaction
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Solubility
• Like dissolves like
• Test for polar substance- dissolve in water
• Non polar solvents clean non polar stains
• Polar solvents clean polar stains
• Oil and water