Date post: | 11-Jan-2016 |
Category: |
Documents |
Upload: | oliver-barrett |
View: | 216 times |
Download: | 4 times |
Molecules of Life
Chapter 2
Part 1
2.1 Impacts/IssuesFear of Frying
All living things consist of the same kinds of molecules, but small differences in the ways they are put together have big effects on health
Artificial trans fats found in manufactured and fast foods raise cholesterol and increase risk of atherosclerosis, heart attack, and diabetes
Video: Fear of frying
Fear of Frying
Trans fats are made by adding hydrogen atoms to liquid vegetable oils
Fig. 2-1, p. 20
trans fatty acid
2.2 Start With Atoms
All substances consist of atoms
Atom• Fundamental building-block particle of matter
Life’s unique characteristics start with the properties of different atoms
Subatomic Particles and Their Charge
Atoms consist of electrons moving around a nucleus of protons and neutrons
Electron (e-) • Negatively charged subatomic particle that
occupies orbitals around the atomic nucleus
Charge• Electrical property of some subatomic particles• Opposite charges attract; like charges repel
Subatomic Particles in the Nucleus
Nucleus• Core of an atom, occupied by protons and
neutrons
Proton (p+)• Positively charged subatomic particle found in the
nucleus of all atoms
Neutron• Uncharged subatomic particle found in the atomic
nucleus
An Atom
Fig. 2-2a, p. 21
an atom
Elements: Different Types of Atoms
Atoms differ in numbers of subatomic particles
Element• A pure substance that consists only of atoms with
the same number of protons
Atomic number• Number of protons in the atomic nucleus• Determines the element
Elements in Living Things
The proportions of different elements differ between living and nonliving things
Some atoms, such as carbon, are found in greater proportions in molecules made only by living things – the molecules of life
Same Elements, Different Forms
Isotopes • Forms of an element that differ in the number of
neutrons their atoms carry• Changes the mass number, but not the charge
Mass number• Total number of protons and neutrons in the
nucleus of an element’s atoms
Radioactive Isotopes
Radioisotope• Isotope with an unstable nucleus, such as
carbon 14 (14C)
Radioactive decay• Process by which atoms of a radioisotope
spontaneously emit energy and subatomic particles when their nucleus disintegrates
Carbon 14: A Radioisotope
Most carbon atoms have 6 protons and 6 neutrons (12C)
Carbon 14 (14C) is a radioisotope with six protons and eight neutrons
When 14C decays, one neutron splits into a proton and an electron, and the atom becomes a different element – nitrogen 14 (14N)
Radioactive Tracers
Researchers introduce radioisotope tracers into living organisms to study the way they move through a system
Tracers• Molecules with a detectable substance attached,
often a radioisotope• Used in research and clinical testing
Why Electrons Matter
Electrons travel around the nucleus in different orbitals (shells) – atoms with vacancies in their outer shells tend to interact with other atoms• Atoms get rid of vacancies by gaining or losing
electrons, or sharing electrons with other atoms
Shell model• Model of electron distribution in an atom
Shell Models
Fig. 2-3 (top), p. 22
Fig. 2-3 (a-c), p. 22
Fig. 2-3 (a-c), p. 22
1 proton 1 21 electron
first shell hydrogen (H) helium (He)
6 8 10
second shell carbon (C) oxygen (O) neon (Ne)
11 17 18
third shell sodium (Na) chlorine (Cl) argon (Ar)
Fig. 2-3 (a-c), p. 22
Stepped Art
1 proton 1 21 electron
first shell hydrogen (H) helium (He)
A) The first shell corresponds to the first energy level, and it can hold up to 2 electrons. Hydrogen has one proton, so it has one vacancy. A helium atom has 2 protons, and no vacancies. The number of protons in each shell model is shown.
6 8 10
second shell carbon (C) oxygen (O) neon (Ne)
B) The second shell corresponds to the second energy level, and it can hold up to 8 electrons. Carbon has 6 protons, so its first shell is full. Its second shell has 4 electrons, and four vacancies.Oxygen has 8 protons and two vacancies. Neon has 10 protons and no vacancies.
11 17 18
third shell sodium (Na) chlorine (Cl) argon (Ar)
C) The third shell, which corresponds to the third energy level, can hold up to 8 electrons, for a total of 18. A sodium atom has 11 protons, so its first twoshells are full; the third shell has one electron. Thus, sodium has seven vacancies. Chlorine has 17 protons and one vacancy. Argon has 18 protons and no vacancies.
Animation: Shell models of common elements
Ions
The negative charge of an electron balances the positive charge of a proton in the nucleus
Changing the number of electrons may fill its outer shell, but changes the charge of the atom
Ion• Atom that carries a charge because it has an
unequal number of protons and electrons
Ion Formation
Fig. 2-4, p. 23
electron loss
Sodium atom
1111p+
11e–
charge: 0
Sodium ion
11p+11
charge: +110e–
electron gain
Chlorine atom
17 17p+
17e–
charge: 0
Chloride ion
18e–
17 17p+
charge: –1
Fig. 2-4a, p. 23
Fig. 2-4a, p. 23
electron gain Chlorine
atom
17 17p+
17e–
charge: 0
Chloride ion
18e–1717p+
charge: –1
Fig. 2-4b, p. 23
Fig. 2-4b, p. 23
electron loss Sodium
atom
11 11p+
11e–
charge: 0
Sodium ion
11p+11
charge: +1
10e–
Fig. 2-4, p. 23
Sodium atom
1111p+
11e–
charge: 0
electron loss
Sodium ion
11p+11
charge: +110e–
Stepped Art
Chlorine atom
17 17p+
17e–
charge: 0
electron gain
Chloride ion
18e–
17 17p+
charge: –1
Animation: How atoms bond
Animation: PET scan
Animation: The shell model of electron distribution
Animation: Subatomic particles
Animation: Atomic number, mass number
Animation: Electron arrangements in atoms
Animation: Isotopes of hydrogen
Video: ABC News: Nuclear Energy
Animation: Electron distribution
2.3 From Atoms to Molecules
Atoms can also fill their vacancies by sharing electrons with other atoms
A chemical bond forms when the electrons of two atoms interact
Chemical bond• An attractive force that arises between two atoms
when their electrons interact
From Atoms to Molecules
Molecule• Group of two or more atoms joined by chemical
bonds
Compound• Type of molecule that has atoms of more than
one element
Referring to a Molecule
Same Materials, Different Results
Animation: Building blocks of life
Ionic Bonds and Covalent Bonds
Depending on the atoms, a chemical bond may be ionic or covalent
Ionic bond• A strong mutual attraction formed between ions of
opposite charge
Covalent bond• Two atoms sharing a pair of electrons
An Ionic Bond: Sodium Chloride
p. 24
ionic bond
11 17
sodium ion (Na+) chloride ion (Cl–)
Covalent Bonds
Molecular hydrogen (H—H) and molecular oxygen (O=O)
p. 24
1 1
molecular hydrogen (H2)
8 8
molecular oxygen (O2)
Polarity
A covalent bond is nonpolar if electrons are shared equally, and polar if the sharing is unequal
Polarity• Any separation of charge into distinct positive and
negative regions
Polar and Nonpolar Covalent Bonds
Nonpolar• Having an even distribution of charge• When atoms in a covalent bond share electrons
equally, the bond is nonpolar
Polar• Having an uneven distribution of charge• When the atoms share electrons unequally, the
bond is polar
Importance of Polar Molecules
A water molecule (H-O-H) has two polar covalent bonds – the oxygen is slightly negative and the hydrogens are slightly positive – which allows water to form hydrogen bonds
p. 25
p. 25
1 8 1
water (H2O)
Hydrogen Bonds
Hydrogen bond• Attraction that forms between a covalently
bonded hydrogen atom and another atom taking part in a separate covalent bond
p. 25
hydrogen bond
Importance of Hydrogen Bonds
Hydrogen bonds form and break more easily than covalent or ionic bonds – they do not form molecules
Hydrogen bonds impart unique properties to substances such as water, and hold molecules such as DNA in their characteristic shapes
Animation: Ionic bonding
Animation: Examples of hydrogen bonds
Video: ABC News: Fuel Cell Vehicles
Animation: Sucrose synthesis
Animation: Covalent bonds
2.4 Water
All living organisms are mostly water, and all chemical reactions of life are carried out in water
Hydrogen bonds between water molecules give water unique properties that make life possible• Capacity to dissolve many substances• Cohesion (surface tension)• Temperature stability
Polarity and theUnique Properties of Water
Fig. 2-7a, p. 26
Fig. 2-7a, p. 26
slight negative charge
slight positive charge slight positive charge
Fig. 2-7b, p. 26
Fig. 2-7c, p. 26
Animation: Structure of water
Water and Solutions
Polar water molecules hydrogen-bond to other polar (hydrophilic) substances, and repel nonpolar (hydrophobic) substances
Hydrophilic (water-loving)• A substance that dissolves easily in water
Hydrophobic (water-dreading)• A substance that resists dissolving in water
Water and Solutions
Water is an excellent solvent
Solvent• Liquid that can dissolve other substances
Solute• A dissolved substance
Water and Solutions
Salts, sugars, and many polar molecules dissolve easily in water
Salt• Compound that dissolves easily in water and
releases ions other than H+ and OH-
• Example: sodium chloride (NaCl)
Water and Solutions
Water molecules surround the atoms of an ionic solid and pull them apart, dissolving it
Animation: Spheres of hydration
Temperature Stability
Temperature stability is an important part of homeostasis• Water absorbs more heat than other liquids
before temperature rises• Hydrogen bonds hold ice together in a rigid
pattern that makes ice float
Temperature• Measure of molecular motion
Cohesion
Cohesion helps sustain multicelled bodies and resists evaporation
Cohesion• Tendency of water molecules to stick together
Evaporation • Transition of liquid to gas• Absorbs heat energy (cooling effect)
2.5 Acids and Bases
Water molecules separate into hydrogen ions (H+) and hydroxide ions (OH-)
pH• A measure of the number of hydrogen ions (H+) in
a solution• The more hydrogen ions, the lower the pH
Pure water has neutral pH (pH=7)• Number of H+ ions = OH- ions
Acids and Bases
Acid• Substance that releases hydrogen ions in water• pH less than 7
Base• Substance that releases hydroxide ions (accepts
hydrogen ions) in water• pH greater than 7
A pH Scale
Fig. 2-9, p. 27
— 0 battery acid
— 1 gastric fluid
lemon juice— 2 acid rain
cola
— 3vinegar
mo
re a
cid
ic
tomatoes, wine
orange juice
— 4 bananasbeer
— 5 black coffeebread
urine, tea, typical rain
butter— 6 corn
milk— 7 pure water
— 8 seawateregg whiteblood, tears
— 9 detergentsbaking soda
Tums
— 10 hand soaptoothpaste
milk of magnesiahousehold ammonia
— 11
mo
re b
asic
— 12 hair removerbleach
— 13
— 14 drain cleaner
oven cleaner
Animation: The pH scale
Acid Rain
Sulfur dioxide and other airborne pollutants dissolve in water vapor to form acid rain
Buffer Systems
Most molecules of life work only within a narrow range of pH – essential for homeostasis
Buffers keep solutions in cells and tissues within a consistent range of pH
Buffer• Set of chemicals that can keep the pH of a
solution stable by alternately donating and accepting ions that contribute to pH
CO2 and the Bicarbonate Buffer System
CO2 forms carbonic acid in water
• CO2 + H2O → H2CO3 (carbonic acid)
Bicarbonate buffer system• Excess H+ combines with bicarbonate
• H+ + HCO3- (bicarbonate) ↔ H2CO3
Video: ABC News: Bottle Backlash
Video: ABC News: Water Use
Video: ABC News: Water Wars
3D Animation: Dissolution