1 chapter 2 the chemical context of life and properties of water
TRANSCRIPT
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Basics You Should KnowMatterElementsCompoundsAtomsSubatomic ParticlesAtomic Number Atomic Mass IsotopesElectron
Shells/Energy LevelsElectron Orbitals
AP BiologyProton Neutron Electron
Hydrogen1 proton1 electron
Oxygen8 protons8 neutrons8 electrons
+ 0 –
Everything is made of matter Matter is made of atoms
AP Biology
The World of Elements
C
Different kinds of atoms = elementsDifferent kinds of atoms = elements
H
ON
P SNa
K
Mg
Ca
AP Biology
Life requires ~25 chemical elements
About 25 elements are essential for life Four elements make up 96% of living
matter:
• carbon (C) • hydrogen (H)
• oxygen (O) • nitrogen (N) Four elements make up most of
remaining 4%:
• phosphorus (P) • calcium (Ca)
• sulfur (S) • potassium (K)
AP Biology 8
Deficiencies
(a) Nitrogen deficiency(b) Iodine deficiency
(Goiter)
If there is a deficiency of an essential element, disease results
AP Biology 9
Trace Elements
Trace elements Are required by an organism in only minute quantities
Minerals such as Fe and Zn are trace elements
AP Biology
Bonding properties
Effect of electrons electrons determine
chemical behavior of atom
depends on numberof electrons in atom’s outermost shell valence shell
How does this atom behave?How does this atom behave?
AP Biology
Bonding propertiesWhat’s themagic number?
How does this atom behave?How does this atom behave? How does this atom behave?How does this atom behave?
AP Biology
Elements & their valence shells
Elements in the same row have the same number of shellsElements in the same row have the same number of shells
Moving from left to right, each element has a sequential addition of electrons (& protons)Moving from left to right, each element has a sequential addition of electrons (& protons)
AP Biology
Elements & their valence shells
Elements in the same column have the same valence & similar chemical properties
Elements in the same column have the same valence & similar chemical properties
AP Biology
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–
–
Chemical reactivity Atoms tend to
complete a partially filled valence shell
or empty a partially filled valence shell
This tendency drives chemical reactions…This tendency drives chemical reactions…
and creates bondsand creates bonds
Ionic bonding
High electronegativity difference strips valence electrons away from another atom
Electron transfer creates ions (charged atoms)
Cation (positive ion); anion (negative ion)
Ex: Salts (sodium chloride)
Covalent Bonding
Sharing pair of valence electrons
Number of electrons required to complete an atom’s valence shell determines how many bonds will form
Ex: Hydrogen & oxygen bonding in water; methane
Nonpolar covalent bond
Pair of electrons shared equally by 2 atoms example: hydrocarbons = CxHx
methane (CH4 )
balanced, stable,good building block
AP Biology
H
H
Oxygen
Polar covalent bonds Pair of electrons shared
unequally by 2 atoms example: water = H2O
oxygen has higher electronegativity
oxygen has stronger “attraction” for the electrons than hydrogen
water is a polar molecule + vs – poles leads to many interesting
properties of water…
+
+
––
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Hydrogen bonds
Hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom (oxygen or nitrogen)
Properties of Water
Earth is ¾ WaterSupports All of Life
Most animals and plants contain more than 60% water by volume.
All living organisms require water more than any other substance
Properties of Water
1.Cohesion/Adhesion
2.Surface tension
3.Temperature Moderation
4.High specific heat
5.Evaporative cooling
6.Universal solvent
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Water can dissociate Into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions
Changes in the concentration of these ions Can have a great affect on pH in living organisms
H
Hydroniumion (H3O+)
H
Hydroxideion (OH–)
H
H
H
H
H
H
+ –
+
Figure on p. 53 of water dissociating
Effects of Changes in pH
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Acids and BasesAn acid
Is any substance that increases the hydrogen ion concentration of a solution
A base Is any substance that reduces the hydrogen
ion concentration of a solution (more OH- ions)