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CHAPTER 2
The Chemistry of Life
Concept 2.1
Atoms, Ions and Molecules
ELEMENTSElement: pure
substanceCannot be broken down
into other substances by chemical means
25 elements are essential to life
ELEMENTS
4 elements make up 96% of all living matter
Hydrogen (H)Oxygen (O)Nitrogen (N)Carbon (C)
ELEMENTS
Calcium (Ca), phosphorus (P), potassium (K), sulfur (S) most of remaining 4%
Trace elements: less than 0.01 % of body massare essential to lifeE.g.: iodine (I), copper (Cu), fluorine (F),
manganese (Mn), and selenium (Se)
Iodine is a trace element that prevents goiter
COMPOUNDS
COMPOUNDS: substance containing two or more elements combined in a fixed ratio
Compound properties may differ greatly from the elements they contain
H2O – liquid at room temperature, while hydrogen and oxygen are both gases
NaClNaCl – white crystal (table salt), while sodium is a silver-gray metal and chlorine is a yellowish-green gas
Na+ + Cl- NaCl
ATOMS
Atom: smallest possible particle of an element
Made up of 3 subatomic particles:proton: single unit of (+) charge
electron: single unit of (-) charge
neutron: electrically neutral—no charge
ATOMIC NUCLEUS
Forms central core of atom
Made up of tightly packed protons and neutrons
Nucleus has a net (+) charge due to the protons it contains
ATOMIC NUMBERAll the atoms of a particular element
have the same number of protons
Atomic number: the number of protons in the nucleus of an element
Examples: Carbon has 6 protons atomic number is 6
Helium has atomic number of 2 helium has 2 protons
ELECTRONSSmall negatively
charged particles that travel around nucleus
Pictured as traveling
around nucleus in a “cloud”
ELECTRONS & REACTIVITY
Electrons are said to belong to different energy levels
First or lowest level contains 2 electrons and is closest to nucleus
Each of the other energy levels contains 8 electrons.
ELECTRON ENERGY LEVELS
If the outer most shell is not filled, the atom is reactive.
The electrons in the outermost shell are called valence electrons.
Valence Electrons (Bohr Model)
Valence Electrons (Lewis Structure)
Concept 4.3
CHEMICAL BONDS JOIN ATOMS TO ONE ANOTHER
CHEMICAL BONDS
Atoms react with one another to fill their outer energy levels One atom may transfer an electron to another
atom or two atoms may share electrons
Transferring or sharing electrons creates an attraction called a chemical bond that holds atoms together
IONIC BONDS
Ionic bond: one atom transfers an electron to another atom
Ions: atoms that become electrically charged as a result of gaining or losing an electron
Oppositely charged ions are attracted to one another forming a chemical bond an ionic bond
COVALENT BONDS
Formed when atoms share electrons
Electrons may be shared equally or unequally
Molecule: two or more atoms held together by covalent bonds
CHEMICAL REACTIONS
Breaking of old chemical bonds and formation of new chemical bonds resulting in the formation of new substances
Reactants: starting material for a chemical reaction
Products: material created as a result of a chemical reaction
CHEMICAL EQUATION
Concept 4.4
LIFE DEPENDS ON THE UNIQUE
PROPERTIES OF WATER
WATER MOLECULEWater is a polar molecule
Electrons in bond are not shared equally between hydrogen and oxygen
Electrons attracted to oxygen more strongly than to hydrogen
Results in an internal separation of charge
Note: Hydrogen atoms in the water molecule are slightly positive and the oxygen atom slightly negative
POLARITY & HYDROGEN BONDING
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WATER’S LIFE-SUPPORTING PROPERTIES
Polarity of water and effects of hydrogen bonding give water with unique properties:
Cohesion and adhesion
Temperature moderation
Low density of ice compared to water
Ability to dissolve substances
COHESION & ADHESION
Cohesion: an attraction between like moleculesWater’s polarity results in hydrogen bonds forming
between water moleculesAdhesion: an attraction between unlike
moleculesBoth cohesion and adhesion are important forces in
the living world
COHESION & ADHESIONKeep large molecules
organized so they function properly in cells
Help transport water through roots and leaves in plants
Provides surface tension on surfaces of ponds and lakes
TEMPERATURE MODERATION
Hydrogen bonds in water molecules allow water temperatures to change more slowly
Causes oceans and lakes to moderate temperatures of nearby land areas less extreme temperatures in coastal areas
Through evaporation (sweating), water moderates temperature absorbs heat energy from skin cooling the body
LOW DENSITY OF ICE
Density: amount of matter/given volume
For most substances, solids are more dense than liquid state of matter
Due to hydrogen bonding, water is the opposite
Liquid water more dense than solid water
Since less dense substances float in more dense substances, ice floats
LOW DENSITY OF ICE
Why is this important to living things?
If ice sank, bodies of water would freeze from the bottom up
Organisms could NOT get to nutrients on the bottom and would be trapped
Ice insulates the water below, allowing life to persist below the frozen surface
WATER DISSOLVES OTHER SUBSTANCES
Solution: uniform mixture of two or more substances
Solvent: the substance that dissolves the other substance; present in the greater amount
Solute: the substance that is dissolved; present in the lesser amount
Aqueous solution: solution where water is the solvent
SOLUTIONS
Salt Dissolving in Water.url
ACIDS, BASES, & pH
Acid: a compound that donates H+ ions to aqueous solutions
Base: a compound that removes H+ ions from an aqueous solution
pH scale: range of numbers that describes how acidic or how basic a solution is
pH scale ranges from 0 (most acidic) to 14 (most basic); pH of 7 is neutral
ACIDS, BASES, & pH
BUFFERSBuffers: substances that cause a solution to
resist changes in pH
Molecules in cells are very sensitive to even small changes in pH
Many biological fluids such as blood contain buffers that maintain its pH at or very near 7.4
THE END
BUFFERS
Buffers.url
COVALENT BONDS
covalent bond.url
Save Video - ionic bonds.url
STABLE ISOTOPES
Most isotopes are stable—their nuclei do not change over time
Other isotopes contain nuclei that will change or decay over time
ionic and covalent bonds .url
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