Download The Nature of Molecules Outline Atomic Structure All matter is

Outline
The Nature of Molecules
•
•
•
•
•
•
Describe the basic structure of an atom
Recognize the importance of electrons
Understand isotopes and radioactivity
Describe chemical bonds and why they form
Be aware of the properties of water
Understand pH and buffers
Atomic Structure
All matter is composed of atoms.
Understanding the structure of atoms is
critical to understanding the nature of
biological molecules.
Structure of an Atom
Atomic Structure
Atoms are composed of
-protons – positively charged particles
-neutrons – neutral particles
-electrons – negatively charged particles
Atomic Number & Mass Number
–
–
2e–
+
+
+
+
Electron
cloud
Nucleus
Helium atom
2
+
Neutrons
2
2
Protons
–
Atomic number = 2
Mass number = 4
Electrons
1
Periodic Table of the Elements
Atomic Structure
Neutral atoms have the same number of protons
and electrons.
Ions are charged atoms.
-cations – have more protons than electrons and
are positively charged
-anions – have more electrons than protons and
are negatively charged
Isotopes of Carbon
Radioactive Decay
neutron
proton
Chart of Isotopes
Radioactivity
Beta – neutron decay to loss of electron
+ electron
Alpha – loss of two neutrons and two protons
Gamma – loss of energy
Carbon
14
Nitrogen
14
2
Radioactive
Dating
Radioactive isotope
half life
C-14 5730 years
H-3
12.25 years
U-238 4.5 billion years
Summary of Isotopes
90 naturally occurring elements
270 stable isotopes
50 natural radioisotopes
1000’s artificial isotopes
Radioactivity
Energy from different sources
Energy (MJ/kg)
16
9-30
39
45
500,000
Source
Firewood
Coal
Natural Gas
Crude oil
Uranium
(nuclear fission)
Atomic Structure
1. Electrons travel in orbitals
2. Electrons have energy levels
Nuclear in origin
Releases energy energy (alpha, beta, gamma)
Uses: Energy, Dating Materials, Research & Medicine
2
Elements
Octet rule: Atoms tend to establish
completely-full outer energy levels.
Outermost
energy level
Electrons
increase in #
8
8
Periodic Table Groups &
Valence Electrons
Energy
Levels
Increase
Group 1
Number
of Outer
Energy
Electrons
1
2
3
4
5
6
7
8
2
3
4
5
6
7
8
3
Electron Energy Levels
Valence electrons are the electrons in the
outermost energy level of an atom.
An element’s chemical properties depend on interactions between
valence electrons of different atoms.
Chemical Bonds
Molecules are groups of atoms held
together in a stable association.
Compounds are molecules containing
more than one type of element.
Atoms are held together in molecules or
compounds by chemical bonds.
Chemical Bonds
Chemical Bonds
Molecules Have Emergent Properties
Ionic bonds are formed by the
attraction of oppositely charged ions.
Sodium
Chemical Bonds
Chlorine
Sodium Chloride
Chemical Bonds
Covalent bonds form when atoms share 2 or
more valence electrons.
Covalent bond strength depends on the number of
electron pairs shared by the atoms.
single
bond
<
double
bond
<
triple
bond
4
Water Structure and Hydrogen Bonding
Water Structure and Hydrogen Bonding
(–)
Hydrogen
bond
(+)
H
(+)
O
(–)
(–)
H (+
)
(–)
(+)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Properties of Water
Fig. 2.15(TE Art)
Properties of Water
High Surface Tension
Cohesion
Adhesion
Properties of Water
Fig. 2.11b
Ice Formation
Properties of Water
2260 kJ.kg-1
Heat of vaporization
High Specific Heat
High Heat of Vaporization
Specific Heat
Air
1.0 J g-1
Water 4.2 J g-1
Water
Ice
5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 2.17(TE
Art)
Properties
of Water
Cl–
forms
Hydration
Shells
Cl–
Na+
Properties of Water - Summary
Solvent
Na+
Cl–
1. Hydrogen bonding between water molecules
2. Cohesion, adhesion & surface tension
3. Specific heat Æ High
4. Heat of vaporization Æ High
Na+
5. Ice Æ less dense than liquid water
Na+
Cl–
6. Solvent Æ great with polar/charged molecules
Salt
crystal
Water
molecules
Acids and Bases
Acids and Bases
• Most biological buffers consist of a pair of
molecules, one an acid and one a base.
34
Acids and Bases
• Acid: a chemical that releases H+1 ions.
• Base: a chemical that accepts H+1 ions.
END Basic Chemistry
• Buffer: a chemical that accepts/releases
H+1 as necessary to keep pH constant
35
6