bio ch02 chemistry basis
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2.1 Atoms, Ions, and Molecules
KEY CONCEPTAll living things are based on atoms and their interactions.
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2.1 Atoms, Ions, and Molecules
• refers to anything that has mass and takes up space.– 92 naturally occurring elements.
- Only six make up 98% body weight of organisms.
· CHNOPS
Matter
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2.1 Atoms, Ions, and Molecules
Living and non-living matter consist of atoms of different elements.• An atom is the smallest basic unit of matter.• An element is one type of atom.
H
O
Hydrogen atom (H)
Oxygen atom (O)
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2.1 Atoms, Ions, and Molecules
– The nucleus has protons and neutrons.– Electrons are in energy levels outside nucleus.
Oxygen atom (O)
Nucleus:8 protons (+)8 neutrons
outermost energy level: 6 electrons (-)
inner energy level: 2 electrons (-)
• An atom has a nucleus and electrons.
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2.1 Atoms, Ions, and Molecules Atomic Number
• Number of protons in the nucleus Atomic mass/ mass number
• Sum of the protons and neutrons in the nucleus Isotopes
• Atom of the same element having the same atomic number but different mass number due to number of neutrons
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2.1 Atoms, Ions, and Molecules
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2.1 Atoms, Ions, and Molecules
– water (H2O)
OHH
_
++
• Elements- 92 naturally occurring and 6 found in living things
• A compound is made of atoms of different elements bonded together.
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2.1 Atoms, Ions, and Molecules
– carbon dioxide (CO2)
• A compound is made of atoms of different elements bonded together.
– water (H2O)
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2.1 Atoms, Ions, and Molecules
– many other carbon-based compounds in living things
• A compound is made of atoms of different elements bonded together.
– water (H2O)
– carbon dioxide (CO2)
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2.1 Atoms, Ions, and Molecules
Ions form when atoms gain or lose electrons.
• An ion is an atom that has gained or lost one or more electrons.– positive ions– negative ions
• Ionic bonds form between oppositely charged ions.
Sodium atom (Na) Chlorine atom (CI) Sodium ion (Na+) Chloride ion (CI-)
Na loses anelectron to CI ionic bond
gained electron
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2.1 Atoms, Ions, and Molecules
Atoms share pairs of electrons in covalent bonds.
• A covalent bond forms when atoms share a pair of electrons.
covalent bonds
Oxygen atom (O) Carbon atom (C) Oxygen atom (O)
Carbon dioxide (CO2 )
– multiple covalent bonds– diatomic molecules
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2.1 Atoms, Ions, and Molecules
KEY CONCEPTWater’s unique properties allow life to exist on Earth.
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2.1 Atoms, Ions, and Molecules
OHH
_
++
Life depends on hydrogen bonds in water.
• Water is a polar molecule.– Polar molecules have slightly charged regions.
– Nonpolar molecules do not have charged regions.– Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms.
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2.1 Atoms, Ions, and Molecules
OH
H
_
+
+
OH
H
_
+
+
OHH
_
++
OHH
_
++
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2.1 Atoms, Ions, and Molecules
• Hydrogen bonds are responsible for important properties of water.
– High heat capacityLarge number of hydrogen bonds absorb heat without
a large change in temperature.
Properties of Water
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2.1 Atoms, Ions, and Molecules
Properties of Water
• High Heat of Vaporization– Large number of hydrogen bonds must be broken to
evaporate water.• Universal Solvent• Cohesive and Adhesive• High Surface Tension
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2.1 Atoms, Ions, and Molecules
Many compounds dissolve in water.
• A solution is formed when one substance dissolves in another.– A solution is a homogeneous mixture.– Solvents dissolve other substances.– Solutes dissolve in a solvent.
solution
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2.1 Atoms, Ions, and Molecules
• “Like dissolves like.”
– Polar solvents dissolve polar solutes.– Nonpolar solvents dissolve nonpolar solutes.– Polar substances and nonpolar substances generally
remain separate.– Hydrophilic molecules
Attract water.– Hydrophobic molecules
Cannot attract water.
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2.1 Atoms, Ions, and Molecules
• “Like dissolves like.”
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2.1 Atoms, Ions, and Molecules
Some compounds form acids or bases.
• An acid releases a hydrogen ion when it dissolves in water.– high H+ concentration– pH less than 7
more acidic
stomach acid pH between 1 and 3
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2.1 Atoms, Ions, and Molecules
• Frozen water is less dense than liquid water Ice acts as an insulator on top of a frozen body of water.
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2.1 Atoms, Ions, and Molecules
• Acids and Bases• pH
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2.1 Atoms, Ions, and Molecules
Some compounds form acids or bases.
• An acid releases a hydrogen ion when it dissolves in water.– high H+ concentration– pH less than 7
more acidic
stomach acid pH between 1 and 3
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2.1 Atoms, Ions, and Molecules
• Base
– either removes hydrogen ions (H+) or release hydroxide ions (OH-).
– low H+ concentration– pH greater than 7
bile pH between 8 and 9
more basic
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2.1 Atoms, Ions, and Molecules
• A neutral solution has a pH of 7.
pure water pH 7
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2.1 Atoms, Ions, and Molecules
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2.1 Atoms, Ions, and Molecules