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Life’s Chemical Basis : 

Life’s Chemical Basis Chapter 2

Impacts, Issues:What Are You Worth? : 

Impacts, Issues:What Are You Worth? Fifty-eight elements make up the human body

1.1 Start With Atoms : 

1.1 Start With Atoms The behavior of elements, which make up all living things, starts with the structure of individual atoms

Characteristics of Atoms : 

Characteristics of Atoms Atoms are the building blocks of all substances Made up of electrons, protons and neutrons Electrons (e-) have a negative charge Move around the nucleus Nearly negligible in mass Charge is an electrical property Attracts or repels other subatomic particles

Characteristics of Atoms : 

Characteristics of Atoms The nucleus contains protons and neutrons Protons (p+) have a positive charge Neutrons have no charge Atoms differ in number of subatomic particles Atomic number= number of protons Number on periodic table Determines identity of the element Elements consist only of atoms with the same atomic number

Atomic Number identifies the element : 

Atomic Number identifies the element Atoms differ in number of subatomic particles Atomic number= number of protons Number on periodic table Determines identity of the element Elements consist only of atoms with the same atomic number

Characteristics of Atoms : 

Characteristics of Atoms Isotopes Naturally occuring Different numbers of neutrons For example, 12C 13C 14C Mass number # Protons + # Neutrons Used to identify isotopes

Atoms : 

Atoms

Slide 9: 

Fig. 2-2, p. 22 proton neutron electron

The Periodic Table : 

The Periodic Table Periodic table of the elements An arrangement of the elements based on their atomic number and chemical properties Created by Dmitry Mendeleev

Periodic Table of the Elements : 

Periodic Table of the Elements

2.2 Putting Radioisotopes to Use : 

2.2 Putting Radioisotopes to Use Some radioactive isotopes – radioisotopes – are used in research and medical applications

Radioisotopes : 

Radioisotopes Henri Becquerel discovered radioisotopes of uranium in the late 1800s Radioactive decay Radioisotopes emit subatomic particles of energy when their nucleus breaks down, transforming one element into another at a constant rate Example: 14C → 14N

Tracers : 

Tracers Tracer Any molecule with a detectable substance attached Examples: CO2 tagged with 14C used to track carbon through photosynthesis Radioactive tracers used in medical PET scans

PET Scanning : 

PET Scanning

Slide 16: 

Fig. 2-4a, p. 23 A A patient is injected with a radioactive tracer and moved into a scanner like this one. Detectors that intercept radioactive decay of the tracer surround the body part of interest.

Slide 17: 

Fig. 2-4b, p. 23

Slide 18: 

Fig. 2-4b, p. 23 tumors B Radioactive decay detected by the scanner is converted into digital images of the body’s interior. Two tumors (blue) in and near the bowel of a cancer patient are visible in this PET scan.

Animation: PET scan : 

Animation: PET scan

2.1-2.2 Key Concepts:Atoms and Elements : 

2.1-2.2 Key Concepts:Atoms and Elements Atoms are particles that are the building blocks of all matter; they can differ in numbers of protons, electrons, and neutrons Elements are pure substances, each consisting entirely of atoms with the same number of protons

2.3 Why Electrons Matter : 

2.3 Why Electrons Matter Atoms acquire, share, and donate electrons Whether an atom will interact with other atoms depends on how many electrons it has All atoms WANT 8 electrons in their OUTER shell because this is MOST STABLE

Atoms and Energy Levels : 

Atoms and Energy Levels Electrons move around nuclei in orbitals Each orbital holds two electrons Each orbital corresponds to an energy level An electron can move in only if there is a vacancy vacancy no vacancy

Why Atoms Interact : 

Why Atoms Interact The shell model of electron orbitals diagrams electron vacancies; filled from inside out First shell: one orbital (2 electrons) Second shell: four orbitals (8 electrons) Third shell: four orbitals (8 electrons) Atoms with vacancies in their outer shell tend to give up, acquire, or share electrons

Shell Models : 

Shell Models

Slide 25: 

Fig. 2-5a, p. 24

Slide 26: 

Fig. 2-5a, p. 24 electron argon 18p+, 18e− sodium 11p+, 11e– chlorine 17p+, 17e– carbon 6p+, 6e– oxygen 8p+, 8e– neon 10p+, 10e– hydrogen 1p+, 1e– helium 2p+, 2e–

Slide 27: 

Fig. 2-5a, p. 24 C) Third shell. This shell corresponds to the third energy level. It has four orbitals with room for eight electrons. Sodium has one electron in the third shell; chlorine has seven. Both have vacancies, so both form chemical bonds. Argon, with no vacancies, does not. B) Second shell. This shell, which corresponds to the second energy level, has four orbitals—room for a total of eight electrons. Carbon has six electrons: two in the first shell and four in the second. It has four vacancies. Oxygen has two vacancies. Both carbon and oxygen form chemical bonds. Neon, with no vacancies, does not. A) First shell. A single shell corresponds to the first energy level, which has a single orbital that can hold two electrons. Hydrogen has only one electron in this shell, so it has one vacancy. A helium atom has two electrons (no vacancies), so it does not form bonds. Stepped Art

Animation: The shell model of electron distribution : 

Animation: The shell model of electron distribution

Atoms and Ions : 

Atoms and Ions Ion An atom with a positive or negative charge due to loss or gain of electrons in its outer shell Examples: Na+, Cl- Electronegativity A measure of an atom’s ability to pull electrons from another atom Oxygen , Nitrogen, Fluorine have a LOT of electronegativity

Ion Formation : 

Ion Formation

Slide 31: 

Fig. 2-6, p. 25 Chlorine atom 17p+ 17e– ______ no net charge electron loss electron gain Chloride ion 17p+ 18e– ______ net negative charge Sodium ion 11p+ 11e– ______ no net charge Sodium atom 11p+ 10e– ______ net positive charge

Slide 32: 

Fig. 2-6, p. 25 Stepped Art

Animation: How atoms bond : 

Animation: How atoms bond

From Atoms to Molecules : 

From Atoms to Molecules Chemical bond An attractive force existing between two atoms when their electrons interact Molecule Two or more atoms joined in chemical bonds

Combining Substances : 

Combining Substances Compounds Molecules consisting of two or more elements whose proportions do not vary Example: Water (H2O) Mixture Two or more substances that intermingle but do not bond; proportions of each can vary

A Compound: Water : 

A Compound: Water

2.3 Key Concepts:Why Electrons Matter : 

2.3 Key Concepts:Why Electrons Matter Whether one atom will bond with others depends on the element, and the number and arrangement of its electrons

2.4 What Happens When Atoms Interact? : 

2.4 What Happens When Atoms Interact? The characteristics of a bond arise from the properties of the atoms that participate in it The three most common types of bonds in biological molecules are ionic, covalent, and hydrogen bonds

Different Ways to Represent the Same Molecule : 

Different Ways to Represent the Same Molecule

Ionic Bonding : 

Ionic Bonding Ionic bond A strong mutual attraction between two oppositely charges ions with a large difference in electronegativity (an electron is not transferred) Example: NaCl (table salt)

Ionic Bonds : 

Ionic Bonds

Slide 42: 

Fig. 2-7a, p. 26

Slide 43: 

Fig. 2-7a, p. 26 A A crystal of table salt is a cubic lattice of many sodium and chloride ions.

Slide 44: 

Fig. 2-7b, p. 26

Slide 45: 

Fig. 2-7b, p. 26 B The mutual attraction of opposite charges holds the two kinds of ions together in a lattice. Chloride ion B 17p+, 18e– Sodium ion. 11p+, 10e–

Animation: Ionic bonding : 

Animation: Ionic bonding

Covalent Bonding : 

Covalent Bonding Covalent bond Two atoms with similar electronegativity and unpaired electrons sharing a pair of electrons Can be stronger than ionic bonds Atoms can share one, two, or three pairs of electrons (single, double, or triple covalent bonds)

Characteristics of Covalent Bonds : 

Characteristics of Covalent Bonds Nonpolar covalent bond Atoms sharing electrons equally; formed between atoms with identical electronegativity Polar covalent bond Atoms with different electronegativity do not share electrons equally; one atom has a more negative charge, the other is more positive

Polarity : 

Polarity Polarity Separation of charge into distinct positive and negative regions in a polar covalent molecule Example: Water (H2O)

Covalent Bonds : 

Covalent Bonds

Slide 51: 

Fig. 2-8, p. 27 Molecular hydrogen (H—H) Two hydrogen atoms, each with one proton, share two electrons in a nonpolar covalent bond. Molecular oxygen (O=O) Two oxygen atoms, each with eight protons, share four electrons in a double covalent bond. Water molecule (H—O—H) Two hydrogen atoms share electrons with an oxygen atom in two polar covalent bonds. The oxygen exerts a greater pull on the shared electrons, so it has a slight negative charge. Each hydrogen has a slight positive charge.

Hydrogen Bonding : 

Hydrogen Bonding Hydrogen bond A weak attraction between a highly electronegative atom and a hydrogen atom taking part in a separate polar covalent bond Hydrogen bonds do not form molecules and are not chemical bonds Hydrogen bonds stabilize the structures of large biological molecules

Hydrogen Bonds : 

Hydrogen Bonds

Slide 54: 

Fig. 2-9a, p. 27

Slide 55: 

Fig. 2-9a, p. 27 hydrogen bond A A hydrogen (H) bond is an attraction between an electronegative atom and a hydrogen atom taking part in a separate polar covalent bond. water molecule water molecule

Slide 56: 

Fig. 2-9b, p. 27

Slide 57: 

Fig. 2-9b, p. 27 B Hydrogen bonds are individually weak, but many of them form. Collectively, they are strong enough to stabilize the structures of large biological molecules such as DNA, shown here.

Animation: Examples of hydrogen bonds : 

Animation: Examples of hydrogen bonds

2.4 Key Concepts:Atoms Bond : 

2.4 Key Concepts:Atoms Bond Atoms of many elements interact by acquiring, sharing, and giving up electrons Ionic, covalent, and hydrogen bonds are the main interactions between atoms in biological molecules

2.5 Water’s Life-Giving Properties : 

2.5 Water’s Life-Giving Properties Living organisms are mostly water; all the chemical reactions of life are carried out in water Water is essential to life because of its unique properties The properties of water are a result of extensive hydrogen bonding among water molecules

Polarity of the Water Molecule : 

Polarity of the Water Molecule Overall, water (H2O) has no charge The water molecule is polar Oxygen atom is slightly negative Hydrogen atoms are slightly positive Hydrogen bonds form between water molecules Gives water unique properties

Water: Essential for Life : 

Water: Essential for Life

Slide 63: 

Fig. 2-10a, p. 28

Slide 64: 

Fig. 2-10a, p. 28 slight negative charge on the oxygen atom A The polarity of a water molecule arises because of the distribution of its electrons. The hydrogen atoms bear a slight positive charge, and the oxygen atom bears a slight negative charge. slight positive charge on the hydrogen atoms

Slide 65: 

Fig. 2-10b, p. 28

Slide 66: 

Fig. 2-10b, p. 28 B Many hydrogen bonds (dashed lines) that form and break rapidly keep water molecules clustered together in liquid water.

Slide 67: 

Fig. 2-10c, p. 28

Slide 68: 

Fig. 2-10c, p. 28 C Below 0°C (32°F), the hydrogen bonds hold water molecules rigidly in the three-dimensional lattice of ice. The molecules are less densely packed in ice than in liquid water, so ice floats on water. The Arctic ice cap is melting because of global warming. It will probably be gone in fifty years, and so will polar bears. Polar bears must now swim farther between shrinking ice sheets, and they are drowning in alarming numbers.

Animation: Structure of water : 

Animation: Structure of water

Water’s Solvent Properties : 

Water’s Solvent Properties Solvent A substance (usually liquid) that can dissolve other substances (solutes) Water is a solvent The collective strength of many hydrogen bonds pulls ions apart and keeps them dissolved

Water’s Solvent Properties : 

Water’s Solvent Properties Water dissolves polar molecules Hydrogen bonds form between water molecules and other polar molecules Polar molecules dissolved by water are hydrophilic (water-loving) Nonpolar (hydrophobic) molecules are not dissolved by water

Water Molecules Surrounding an Ionic Solid : 

Water Molecules Surrounding an Ionic Solid

Animation: Spheres of hydration : 

Animation: Spheres of hydration

Water’s Temperature-Stabilizing Effects : 

Water’s Temperature-Stabilizing Effects Compared with other molecules, water absorbs more heat before it becomes measurably hotter Temperature A way to measure the energy of molecular motion Molecules move faster as they absorb heat

Water’s Temperature-Stabilizing Effects : 

Water’s Temperature-Stabilizing Effects The surface temperature of water decreases during evaporation Evaporation Conversion of a liquid to a gas by heat energy Ice is less dense than liquid water Hydrogen bonds form a lattice during freezing

Water’s Cohesion : 

Water’s Cohesion Hydrogen bonds give water cohesion Provides surface tension Draws water up from roots of plants Cohesion Molecules resist separation from one another

Cohesion of Water : 

Cohesion of Water

2.5 Key Concepts:Water of Life : 

2.5 Key Concepts:Water of Life Life originated in water and is adapted to its properties Water has temperature-stabilizing effects, cohesion, and a capacity to act as a solvent for many other substances These properties make life possible on Earth

2.6 Acids and Bases : 

2.6 Acids and Bases Hydrogen ions have far-reaching effects because they are chemically active, and because there are so many of them Chemical reactions involving acids and bases are important to homeostasis

Biological Reactions Occur In Water : 

Biological Reactions Occur In Water Molecules in water (H2O) can separate into hydrogen ions (H+) and hydroxide ions (OH-) H20 ↔ H+ + OH-

The pH Scale : 

The pH Scale pH is a measure of the number of hydrogen ions in a solution The more hydrogen ions, the lower the pH pH 7 is neutral (pure water) Most life chemistry occurs around pH7

A pH Scale : 

A pH Scale

Slide 83: 

Fig. 2-13, p. 30 0 — 100 battery acid 1— 10–1 gastric fluid 2 — 10–2 acid rain lemon juice cola 3 — 10–3 orange juice tomatoes, wine vinegar more acidic 4 — 10–4 bananas beer 5 — 10–5 coffee bread urine, tea, typical rain 6 — 10–6 corn butter milk 7 — 10–7 pure water blood, tears 8 — 10–8 seawater egg white baking soda 9 — 10–9 phosphate detergents Tums 10 — 10–10 hand soap milk of magnesia toothpaste 11— 10–11 household ammonia more basic 10–12 hair remover 12 — bleach 13 — 10–13 oven cleaner 14 — 10–14 drain cleaner

Animation: The pH scale : 

Animation: The pH scale

How Do Acids and Bases Differ? : 

How Do Acids and Bases Differ? Acids donate hydrogen ions in a water solution pH below 7 Bases accept hydrogen ions in a water solution pH above 7

Acids: Weak or Strong : 

Acids: Weak or Strong Acids and bases can be weak or strong Gastric fluid, pH 2-3 Acid rain Example: Hydrochloric acid is a strong acid HCl ↔ H+ + Cl-

Acid Rain : 

Acid Rain Sulfur dioxide dissolves in water vapor to form an acidic solution

Salts and Water : 

Salts and Water Salt A compound that dissolves easily in water and releases ions other than H+ and OH- HCl (acid) + NaOH (base) → NaCl (salt) + H20

Buffers Against Shifts in pH : 

Buffers Against Shifts in pH Buffer system A set of chemicals (a weak acid or base and its salt) that can keep the pH of a solution stable OH- + H2CO3 (carbonic acid) → HCO3- (bicarbonate) + H20 H+ + HCO3- (bicarbonate) → H2CO3 (carbonic acid)

Buffering Carbon Dioxide in Blood : 

Buffering Carbon Dioxide in Blood Carbon dioxide in blood forms carbonic acid, which separates into H+ and bicarbonate H2O + CO2 (carbon dioxide) → H2CO3 (carbonic acid) → H+ + HCO3- (bicarbonate)

2.6 Key Concepts:The Power of Hydrogen : 

2.6 Key Concepts:The Power of Hydrogen Life is responsive to changes in the amounts of hydrogen ions and other substances dissolved in water

Summary: Players in the Chemistry of Life : 

Summary: Players in the Chemistry of Life

Animation: Buffer system : 

Animation: Buffer system

Animation: Covalent bonds : 

Animation: Covalent bonds

Animation: Electron arrangements in atoms : 

Animation: Electron arrangements in atoms

Animation: Isotopes of hydrogen : 

Animation: Isotopes of hydrogen

Animation: Shell models of common elements : 

Animation: Shell models of common elements

ABC video: The Wine of Life : 

ABC video: The Wine of Life

ABC video: Nuclear Energy : 

ABC video: Nuclear Energy

Video: What are you worth? : 

Video: What are you worth?

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