Transcript Chemistry: Atoms, Molecules and Water

Atoms, Molecules
and Water
Essential Building Blocks
for Living Organisms
Comparison of Terms
Atom
Smallest units of matter that can
exist separately.
Element
Chemical substance composed of
the same kind of atoms
Molecule Two or more atoms joined by
chemical bonds
Composition
of an Atom
• Nucleus
Proton = positively charged particle (+)
Neutron = uncharged particle (n or +)
Number of protons + Number of neutrons = Atomic mass
Number of protons = Atomic number
•Electrons = negatively charged particles
Number of electrons = Number of protons
Each electron circles the nucleus in an orbit
representing a specific energy level.
12
6
C
Isotopes
• Forms of same atom that differ in the
number of neutrons
• Less stable isotopes generate
radioactivity
12
6
C
13
6
C
14
6
C
radioactive
Atomic Models
Electron
Shell
Nucleus
Hydrogen (H)
Helium (He)
Different Kinds of Atoms
Innermost
electron shell
8e- +
8n 8p
Oxygen
Max 2e2e- +
2n 2p
+2p+
+2n±
+2e+7p+
+8n±
+7e-
Max 8e-
+4p+
Helium
+4n±
+4e-
15e- +
16n 15p
+5p+
+4n±
+5e
Phosphorus
6e- +
6n 6p
Carbon
20e- +
20n 20p
Calcium
Applying Your Knowledge
Magnesium
Chlorine
Atomic Number
12
17
Atomic Mass
24
35
Number of Protons
Number of Neutrons
Number of Electrons
Electron Energy Levels
Energy Capacity for
Level
Electrons
1
2
2
8
3
8
In forming molecules, atoms combine
to fill their outer energy levels.
Applying Your Knowledge
Total Number of
Electrons
Number of Electrons
in First Electron Shell
Number Electrons in
Second Electron Shell
Number of Electrons
In Third Electron Shell
Magnesium
Chlorine
12
17
Chemical Bonds
Forces holding atoms together
Bond
Ionic
Characteristics
One atom loses an electron,
another gains an electron
Covalent
Atoms share electrons
Polar
Covalent
Hydrogen
Atoms share electrons
unequally
Covalently-bound hydrogen is
attracted to another atom
Positive
charge
Ionic Bonding in NaCl
–
–
–
–
–
–
+±+
+
++±±
±
±
+
±
+
±±±
+
–
–
–
–
–
–
–
–
–
– –
–
–
–
–
–
–
+±+
+
++±±
±
±
+
±
+±±
±
+
–
–
– –
–
–
–
–
–
–
Sodium ion
#e=#p-1
Sodium
#e=2+8+1=#p
–
–
Chlorine
#e=2+8+7=#p
–
–
–
–
–
–
–
+±+
+
++±±
±
±
+
±
+
±±±
+
–
–
Electron
Completely
Transferred
–
–
–
–
+±+
+
++±±
±
±
+
±
+
±±±
+
–
–
–
–
–
–
–
–
Negative
charge
–
Chlorine
ion #e=#p+1
Ionic Bonding in NaCl
• Opposites
attract.
• Sodiums nestle
between
chlorines.
• Perfectly
cubical crystals
form.
Cl- +Cl- +Cl- +Cl-
Na Na Na Na+
Cl- +Cl- +Cl- +Cl- +
- ClNa Na
- Na
- Na
Cl
Cl
Cl
Na-+ Cl
Na+ Na+ Na+
Cl- + Cl- +Cl
+ - Na+ Na Na
Na
ClCl
Cl
Cl
Na-+ Cl
Na-+ Na+ Na+
Cl- +Cl- +Cl
+ - Na+ Na Na
Na
Cl Cl Cl ClNa+ Na+ Na+ Na+
- Cl- Cl-
Cl +Cl
Na
Na+
Na+
Na+
Covalent Bonding
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)
Polar Covalent Bonding
Slightly
positive
Slightly
negative
Slightly
negative
Slightly
positive
Hydrogen Bonds Join Water Molecules
Water molecules
carry slight
charges
Positive and
negative charges
attract
Hydrogen bonds
form between H
of one water
molecule and O
of another
H
H
+
–
O
+
H
+
O
–
+
H
+
Hydrogen
Bonds
Due to Hydrogen Bonding, Water Has
•Cohesion: water molecules associate
with each other
•Liquid at room temperature
•Fills blood vessels
•Flows freely to deliver materials
throughout the body
Due to Hydrogen Bonding,
Water Resists Temperature Change
Water has high values for
Specific Heat: heat needed
to change temperature
-keeps body temperature constant
Heat of Vaporization: heat needed to
convert liquid to gas
-evaporation of sweat uses body heatcooling
Due to Hydrogen Bonding,
Density Decreases Upon Freezing
Ice floats!
Water As a Solvent
• Substances that dissolve in water =
hydrophilic
– Polar
– Ionic
• Substances that are insoluble in
water = hydrophobic
– Non-polar
NaCl Dissolves in Water
Ionic bonds
of NaCl give
+/- charges
Water has
partial +/charges
O tends
to join
with Na+
H tends
to join
with Cl-
Dissociation
–
Water
Hydroxide
ion
+
+
Hydrogen
ion
A few water molecules
naturally dissociate into ions
• Hydroxide ion is negative and basic
• Hydrogen ion is positive and
acidic
Lime
Juice
The pH Scale
Sea
Water
Lemon
Stomach Juice
Acid
0
1
2
Beer
3
4
Urine
Coffee
5
6
Blood
Bleach
Baking
Soda
Water
7
8
9
Oven
Cleaner
Ammonia
10 11 12 13 14
Neutral
[H+] = [OH–]
Increasingly Acidic
[H+] > [OH–]
Increasingly Basic
[H+] < [OH–]
Each 1-unit change in pH represents a tenfold difference in [H+] and [OH-].
[H+] is highest at 0; [OH-] is highest at 14.
From 014, [H+] decreases and [OH-] increases.
From 140, [H+] increases and [OH-] decreases.
Applying Your Knowledge
Given: Coffee has a pH value of 5.
Pure water has a pH value of 7.
Complete this sentence:
Coffee has (A)______ fold
greater (B) _____ than water.
(A)
(B)
1. 1
2. 10
3. 100
4. 1000
5. None is correct
1. [H+]
2. [OH-]
3. [H+] and [OH-]
Maintaining Proper pH of Body Fluids
• Buffer: substance that resists pH
change by combining with H+ or
OH–Example: bicarbonate buffering
system of blood
water
hydrogen ion
bicarbonate ion
carbonic acid
OH- +H2CO3
carbon dioxide
HCO3- + H2O