Chapter 2 Atoms and Molecules: The Chemical Basis of Life.
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Transcript of Chapter 2 Atoms and Molecules: The Chemical Basis of Life.
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Chapter 2
Atoms and Molecules: The Chemical Basis of Life
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Inorganic vs. Organic
Inorganic compounds - simple substances that do not contain carbon Ex. water
Organic compounds – carbon-containing compounds that are large and complex Ex. Glucose
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Organic compounds all contain:
6%0%
94%
0%
1. Oxygen2. Nitrogen3. Carbon4. Zinc
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Elements
Elements – substances that cannot be broken down into simpler substances
4 elements responsible for more than 96% of the mass of most organisms: Oxygen Carbon Hydrogen Nitrogen
See table 2-1 in book p.24
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Other elements that make up living organisms
Calcium Phosphorus Potassium Magnesium Sodium Iron Sulfur
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What is the most abundant element in the human body?
29%
12%
53%
6%
1. Oxygen 2. Carbon3. Hydrogen4. Nitrogen
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Chemistry Quick Review
Atom – the smallest portion of an element that retains its chemical properties
Subatomic particles: Electron – negative charge Proton – positive charge Neutron – uncharged
# of electrons = # of protons Nucleus – protons and neutrons Electrons – move rapidly through space
around nucleus
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Atomic Number
Each kind of element has a fixed number of protons in the atomic nucleus
Written as a subscript to the left of the chemical symbol Example: 8O Oxygen nucleus contains 8 protons Determines the atom’s identity and
defines the element
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Which element has an atomic number of 7?
0% 0%
100%
0%
1. Hydrogen2. Carbon3. Nitrogen4. Helium
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The Periodic Table
Chart in which elements are arranged in order by atomic number
Can be used to determine electron configurations Bohr model – shows the electrons
arranged in a series of concentric circles around the nucleus
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Bohr Model
What element is this?
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Atomic Mass Mass of protons + neutrons Mass of electron = 1/1800 the mass of
a proton or neutron Atomic mass number is a superscript
to the left of the symbol Example: 16O
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Isotopes
Atom with different number of neutrons (different masses)
Most elements mixture of isotopes Ex. Carbon-12, Carbon-14
Mass of element is average of the masses of its isotopes Atomic mass of Carbon = 12.011
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Isotopes
Radioisotopes – unstable isotopes Tend to break down (decay) to a more
stable isotope Emit radiation when they decay Ex. Carbon-14 decays to Nitrogen
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Electrons move in orbitals
Orbitals are more like “electron clouds”
The farther away from the nucleus, the more energy the electrons have
Valence electrons – the most energetic electrons Occupy valence (outer) shell
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Chemical Reactions
Valence electrons participate in chemical reactions
When valence shell is full, it is stable
When valence shell is not full, atoms tend to lose, gain, or share electrons
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To be full, the first electron shell has how many electrons?
0%
94%
0%6%
0%
1. 12. 23. 44. 85. 18
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Compounds and Molecules
Atoms combine to form compounds and molecules
Compounds - 2 or more different elements combined in a fixed ratio Ex. NaCl (table salt)
Molecules - 2 or more atoms combine chemically Ex. O2, DNA
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Are all molecules compounds?
71%
29%
1. Yes2. No
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Molecule or Compound? O2
65%
24%
12%
1. Molecule2. Compound3. Both
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Chemical Formulas
Represents chemical composition Simplest formula – most simple ratio
Ex. NH2
Molecular formula – actual numbers of each type of atom per molecule Ex. N2H4
Structural formula – shows arrangement of atoms Ex. Water H – O – H
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Chemical Equations
Reactants – participate in reaction Products – formed by the reaction Example – cellular respiration C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy
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Chemical Bonds
Valence electrons dictate # of bonds
2 types of chemical bonds: Covalent – atoms share electrons Ionic - attraction between positive
cations and negative anions Transfer electrons
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Covalent Bonds
Ex. H2 gas Each atom has 1 electron 2 electrons fill valence shell Both atoms attract the electrons
(share) Valence shell is full w/ 2 electrons
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Types of Covalent Bonds
Single covalent bond – 1 pair of electrons is shared
Double covalent bond – 2 pairs of electrons shared
Triple covalent bond – 3 pairs of electrons shared
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Covalent Bonds
Electronegativity - measure of atom’s attraction for shared electrons in chemical bonds
Oxygen, Nitrogen, Fluorine, Chlorine very electronegative
Can be polar or nonpolar Similar electronegativities = nonpolar bonds Different electronegativities = polar bonds
Electrons are pulled closer to the nucleus of the atom with the higher electronegativity
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Polar Molecules
Molecule with one or more polar covalent bonds
One end with a partial positive charge and other end a partial negative charge
Ex. Water (p.31)
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A water molecule is polar because
24%
0%
76%1. The electrons orbit
the H atoms more closely
2. The electrons orbit the O atom more closely
3. The electrons orbit all atoms equally
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Ionic Bonds
Ionic compound – consists of anions and cations bonded together
Ex. NaCl (p.31 & 32) Na – 1 valence electron Cl – 7 valence electrons Cl takes electron from Na to complete
valence shell
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Hydrogen Bonds
Weak attractions Important in determining the 3-D
structure of large molecules DNA Proteins
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Why are hydrogen bonds essential to the function of DNA?
33% 33%33%1. They keep the 2
strands tightly bonded together
2. They allow the 2 strands to separate for replication
3. They are strong bonds
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Redox Reactions
Reaction that involves electron transfer
Cellular Respiration and Photosynthesis
Oxidation – atom/ion loses electron Reduction – atom/ion gains electron
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Water
70% of total body weight Reactant/product in many chemical
reactions Solvent for most biological reactions
Hydrophilic – react with water Hydrophobic – not disrupted/dissolved
by water
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Which of the following substances is hydrophobic?
Salt
Suga
r O
il
33% 33%33%1. Salt2. Sugar3. Oil
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Properties of Water
Cohesive – water molecules stick to each other
Adhesive – water molecules stick to other substances
Capillary action – cohesion and adhesion working together Water will move against gravity in a
narrow tube In plants, water moves from soil to roots
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Properties of Water
Surface tension – water molecules crowd together at the surface strong layer
High specific heat Maintains a stable temperature
High heat of vaporization Much heat required to change to water
vapor
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Acids and Bases
Acids – proton donors Acid -> H+ + Anion Acidic solutions have higher hydrogen
ion concentration Turn blue litmus paper red Sour taste HCl – inorganic acid Acetic Acid – from vinegar, Lactic Acid –
from sour milk (organic acids)
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Acids and Bases
Bases – proton acceptors Base -> OH- + Cation Basic solutions have lower hydrogen
ion concentration Turn red litmus paper blue Feel slippery to the touch Ex. Sodium Hydroxide, Ammonia –
inorganic Purine and Pyrimidine – organic
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pH scale
Logarithmic expression of the hydrogen ion concentration of solution
7 = neutral Below 7 = Acid Above 7 = Base