Chapter 2

Matter and Energy

• Matter is anything that occupies space and has mass

• Matter exists in three states: solid, liquid, and gaseous

  • Solids have a definite shape and volume
  • Liquids have a definite volume but take the shape of their container
  • Gases have neither a definite shape nor volume

• Matter can be changed physically or chemically

  • Physical changes do not alter the basic nature of a substance
    • Examples include changes in state (solid, liquid, or gas)
  • Chemical changes alter the chemical composition of a substance

• Energy is the ability to do work

  • Has no mass and does not take up space
  • Types of energy:
    • Kinetic energy: energy in motion
    • Potential energy: stored energy

• Forms of energy:

  • Chemical energy: stored in chemical bonds of substances
  • Electrical energy: results from movement of charged particles
  • Mechanical energy: directly involved in moving matter
  • Radiant energy: travels in waves (electromagnetic spectrum)

• Energy form conversions

  • ATP (adenosine triphosphate) traps the chemical energy of food in its bonds

Composition of Matter

• Elements are fundamental units of matter

  • 96% of the body is made from four elements:
    • Oxygen (O): most common (65% of body mass)
    • Carbon (C)
    • Hydrogen (H)
    • Nitrogen (N)

• Periodic table lists all elements

Atoms

• Building blocks of elements
• Atoms of elements differ
• Atomic symbol is chemical shorthand for each element

The Basic Atomic Subparticles

• Protons (p+) are positively charged
• Neutrons (n°) are uncharged or neutral
• Electrons (e-) are negatively charged
• Atoms are electrically neutral (number of protons equals number of electrons)
• Ions are atoms that have gained or lost electrons

Planetary and Orbital Models of an Atom

• Planetary model:

  • Atom analogous to a miniature solar system
  • Protons and neutrons are in the atomic nucleus
  • Electrons are in orbitals around the nucleus

• Orbital model:

  • Electrons are depicted as an electron cloud, a haze of negative charge outside the nucleus

• Electrons determine an atom's chemical behavior and bonding properties

Identifying Elements

• To identify an element, one needs its atomic number, atomic mass number, and atomic weight.
• Atomic number equals the number of protons in an atom
• Unique to atoms of a specific element
• Indirectly indicates the number of electrons
• Atomic mass number is the sum of protons and neutrons in an atom's nucleus
• Atomic weight is approximately equal to the mass number of the most abundant isotope

Atomic Weight and Isotopes

• Isotopes are atoms with the same number of protons and electrons but different numbers of neutrons
• Isotopes have the same atomic number but different atomic masses
• Radioisotopes are heavy isotopes that are unstable and decompose into more stable isotopes
• Radioactivity is the process of spontaneous atomic decay

Molecules and Compounds

• Molecule: two or more atoms of the same element combined chemically
• Compound: two or more atoms of different elements combined chemically

Chemical Bonds and Chemical Reactions

• Chemical reactions occur when atoms combine with or dissociate from other atoms
• Chemical bonds are energy relationships involving interactions among the electrons of reacting atoms

Role of Electrons

• Electrons occupy energy levels (electron shells)
• Electrons closest to the nucleus are most strongly attracted to it
• Distant electrons are likely to interact with other atoms
• Each electron shell has distinct properties (how to fill an atom's electron shells)
  • Shell 1 has a maximum of 2 electrons
  • Shell 2 has a maximum of 8 electrons
  • Shell 3 has a maximum of 8 electrons
• Subsequent shells can hold more electrons
• Bonding occurs between electrons in the outermost (valence) shell
• Atoms with full valence shells do not form bonds.
• Rule of eights: Atoms are considered stable when their outermost valence shell has 8 electrons, except for shell 1, which can hold only 2 electrons
• Reactive elements gain, lose, or share electrons to complete their outermost orbitals

Types of Chemical Bonds

• Ionic bonds involve complete transfer of electrons between atoms forming ions

  • Anions have negative charges
  • Cations have positive charges
  • Ions stay close together due to opposite charges attract

• Covalent bonds involve sharing electrons between atoms

  • Nonpolar covalent bonds: electrons shared equally
  • Polar covalent bonds: electrons shared unequally
  • Molecule has a positive and negative side (pole)

• Hydrogen bonds are extremely weak chemical bonds formed between a hydrogen atom and a negative portion (oxygen or nitrogen atom) of a polar molecule

Patterns of Chemical Reactions

• Synthesis reaction (A + B → AB): atoms or molecules combine to form a larger, more complex molecule

  • Energy is absorbed for bond formation
  • Represents anabolic activities in the body.

• Decomposition reaction (AB → A + B): a molecule breaks down into smaller molecules

  • Chemical energy is released
  • Represents catabolic activities in the body.

• Exchange reaction (AB + C → AC + B): simultaneous synthesis and decomposition reactions

  • The switch is made among molecule parts and different molecules are formed.

• Most chemical reactions are reversible, indicated by a double arrow

• Factors like temperature or concentration alter reaction rates

Table 2.4 Factors Increasing the Rate of Chemical Reactions

• Factors like temperature, concentration, particle size increase the number of collisions, which in turn increase the rate of chemical reactions shown in Table 2.4

Biochemistry: The Chemical Composition of Living Matter

• Inorganic compounds lack carbon; tend to be small and simple and include water, acids, bases, and salts
• Organic compounds contain carbon, are large covalent molecules, and include carbohydrates, lipids, proteins, and nucleic acids

Inorganic Compounds

• Water: the most abundant inorganic compound in the body (two-thirds of body weight)

  • High heat capacity: absorbs and releases large amounts of heat before changing temperature. Prevents sudden changes in body temperature
  • Polarity/solvent properties: dissolves various solutes (solids, liquids, or gases). Forms solutions
  • Chemical reactivity: important reactant in some chemical reactions (hydrolysis reactions)
  • Cushioning: protective function (cerebrospinal and amniotic fluid)

• Salts: ionic compounds

  • Contain cations other than H+ and anions other than OH-
  • Easily dissociate into ions in water
  • Vital for many body functions, eg; nerve impulses
  • All salts are electrolytes; electrolytes conduct electrical current

• Acids: electrolytes that release hydrogen ions (H+) in water; proton donors

• Bases: electrolytes that release hydroxyl ions (OH) in water; proton acceptors

• Neutralization reaction: exchange reaction where acids and bases react to form water and a salt

• pH: measures relative concentration of hydrogen (and hydroxide) ions in body fluids

  • pH Scale from 0 to 14
    • 7 (neutral) - hydrogen ions equal hydroxyl ions
    • Below 7 (acidic) - more H+ than OH-
    • Above 7 (basic/alkaline) - fewer H+ than OH-
  • Buffers regulate pH changes.

Organic Compounds

• Carbohydrates (contain carbon, hydrogen, and oxygen):

  • Monosaccharides: single sugar (eg., glucose, fructose, ribose)
  • Disaccharides: two sugars joined by dehydration synthesis (eg., sucrose, lactose)
  • Polysaccharides: long chains of linked simple sugars (eg., starch, glycogen)

• Lipids (contain carbon, hydrogen, and oxygen; C and H outnumber O) are insoluble in water, but soluble in other lipids,

  • Triglycerides (neutral fats): found in fat deposits, provide stored energy
    • Saturated fatty acids, unsaturated fatty acids
  • Trans fats: increase heart disease risk
  • Omega-3 fatty acids: decrease heart disease risk
  • Phospholipids: contain two fatty acids chains and a hydrophilic head, form cell membranes

• Steroids: four interlocking rings

  • Cholesterol, bile salts, vitamin D, some hormones
  • Cholesterol: basis for all steroids in the body

• Proteins (account for over half of body's organic matter):

  • Fibrous (structural) proteins: appear in body structures, exhibit secondary, tertiary, and quaternary structures that bind structures together (eg., collagen, keratin)
  • Globular (functional) proteins: function as antibodies, hormones, enzymes, exhibit tertiary structures, have active sites that interact with other molecules (eg., enzymes, antibodies, hormones)

• Nucleic acids (form genes): composed of carbon, oxygen, hydrogen, nitrogen, and phosphorus

  • DNA: genetic material, organized by complementary base pairing, contains deoxyribose sugar and bases: adenine, thymine, cytosine, guanine.
  • RNA: carries out DNA's instructions for protein synthesis, organized by complementary base pairing, contains ribose sugar and bases: adenine, uracil, cytosine, guanine

• ATP (adenosine triphosphate): nucleotide with ribose, adenine, and 3 phosphate groups, chemical energy used by all cells Energy released by breaking high-energy phosphate bonds.

  • ADP is formed from ATP when energy is used