Review concepts:
Chapter 2
Chemical Level of Organization
Chemical level of organization
o First level of studying the human body is chemical level of organization
o Chemistry studies the structure of matter
o Matter
Anything that takes up space and has mass
o Mass
The amount of material in matter
On Earth, mass is equivalent to weight
Atoms – smallest stable units of matter
o Composed of subatomic particles
Protons (p+)
o Have a positive electrical charge
Neutrons (n or n0)
o Are electrically neutral (uncharged)
Electrons (e–)
o Have a negative electrical charge
o Are much smaller than protons or neutrons (about 1/1836
the mass)
o An atom can be subdivided into:
Nucleus
o At the center of an atom
o Contains one or more protons
o May also contain neutrons
o Mass of atom mainly determined by number of protons
and neutrons
Electron cloud
o Created by whirl of electrons around the nucleus
Molecules
o When atoms interact, they produce larger, more complex structures
called molecules
All matter composed of varying arrangements of atoms
Variation in matter characteristics results from types of atoms
and ways they interact
Atoms and elements
© 2015 Pearson Education, Inc.
, o Atoms normally contain equal numbers of protons and electrons
o Atomic number
Total number of protons in an atom
o Mass number
o Total number of protons and neutrons in an atom
o Element
Substance composed only of atoms with same atomic number
Example: hydrogen
Hydrogen (H)
o Simplest atom
o Atomic number of 1
o Contains 1 proton and 1 electron
o Proton in the center of the atom (the nucleus)
o Electron whirls around the nucleus in the electron cloud
Electron cloud
o Area in which electrons whirl around the nucleus
o The negatively charged electron is attracted to the positively charged
proton, so it stays in “orbit”
Example of an electrical force
Electron shell
o Two-dimensional representation of the electron cloud
o Outermost shell represents the surface of the electron cloud
Isotopes
o Atoms with same number of protons but different numbers of neutrons
o Identical chemical properties
o Different mass number
Atomic mass
o Actual mass of an atom of a specific isotope
o Measured in atomic mass units (amu) or daltons
One amu 1/12 mass of a carbon-12 atom
Very close to the weight of one proton or one neutron
Atomic weight
o Equals average mass of an element, including different isotopes in
proportion
o Very close to mass number of most common isotope
o Example:
Hydrogen atomic number = 1 (one proton)
Hydrogen atomic weight = 1.0079
o Not all hydrogen atoms have 0 neutrons
o 0.015 percent have 1 neutron (mass number 2)
o Lower percentage have 2 neutrons (mass number 3)
Elements
o Principal elements
Thirteen most abundant elements by body weight
o Trace elements
Fourteen other elements present in the body in very small
© 2015 Pearson Education, Inc.
, amounts
o All elements represented by a chemical symbol based on:
o English names (e.g., O for oxygen; C for carbon)
o Other language names (e.g., Na for sodium from Latin natrium)
Atoms are electrically neutral
o Every positive proton is balanced by a negative electron
o Electrons occupy an orderly series of energy levels within the electron
cloud
Can be diagrammed as series of concentric electron shells
First shell (closest to nucleus) is the lowest energy level
Number of electrons in outermost shell determines chemical
properties of element
Energy levels
o Outermost energy level (valence shell) is atom’s “surface”
o Atoms with unfilled outer shells are reactive
Tend to react with other atoms to fill outer shell
Examples: hydrogen, lithium
o Atoms with full outer shells are inert
Do not readily react with other atoms; more stable
Examples: helium, neon
o Called noble gases
Ions
o Atoms that have gained or lost electrons and are no longer electrically
neutral
o Losing an electron means:
Fewer electrons (negative) than protons (positive)
Net positive charge
Called a positive ion or cation
One missing electron charge of 1
More electrons missing more positive charge (e.g., 2, 3, 4)
Ions (continued)
o Gaining an electron means:
More electrons (negative) than protons (positive)
Net negative charge
Called a negative ion or anion
One extra electron charge of 1
More electrons gained more negative charge (e.g., 2, 3, 4)
o Stabilizing interactions often form chemical bonds
Chemical bonding creates
o Molecules (substances with two or more atoms)
o Compounds (substances with two or more different atoms)
Ionic bonds
o One of the most common types of chemical bonds
o Created by electrical attraction between cations (positive ions) and
anions (negative ions)
© 2015 Pearson Education, Inc.
Chapter 2
Chemical Level of Organization
Chemical level of organization
o First level of studying the human body is chemical level of organization
o Chemistry studies the structure of matter
o Matter
Anything that takes up space and has mass
o Mass
The amount of material in matter
On Earth, mass is equivalent to weight
Atoms – smallest stable units of matter
o Composed of subatomic particles
Protons (p+)
o Have a positive electrical charge
Neutrons (n or n0)
o Are electrically neutral (uncharged)
Electrons (e–)
o Have a negative electrical charge
o Are much smaller than protons or neutrons (about 1/1836
the mass)
o An atom can be subdivided into:
Nucleus
o At the center of an atom
o Contains one or more protons
o May also contain neutrons
o Mass of atom mainly determined by number of protons
and neutrons
Electron cloud
o Created by whirl of electrons around the nucleus
Molecules
o When atoms interact, they produce larger, more complex structures
called molecules
All matter composed of varying arrangements of atoms
Variation in matter characteristics results from types of atoms
and ways they interact
Atoms and elements
© 2015 Pearson Education, Inc.
, o Atoms normally contain equal numbers of protons and electrons
o Atomic number
Total number of protons in an atom
o Mass number
o Total number of protons and neutrons in an atom
o Element
Substance composed only of atoms with same atomic number
Example: hydrogen
Hydrogen (H)
o Simplest atom
o Atomic number of 1
o Contains 1 proton and 1 electron
o Proton in the center of the atom (the nucleus)
o Electron whirls around the nucleus in the electron cloud
Electron cloud
o Area in which electrons whirl around the nucleus
o The negatively charged electron is attracted to the positively charged
proton, so it stays in “orbit”
Example of an electrical force
Electron shell
o Two-dimensional representation of the electron cloud
o Outermost shell represents the surface of the electron cloud
Isotopes
o Atoms with same number of protons but different numbers of neutrons
o Identical chemical properties
o Different mass number
Atomic mass
o Actual mass of an atom of a specific isotope
o Measured in atomic mass units (amu) or daltons
One amu 1/12 mass of a carbon-12 atom
Very close to the weight of one proton or one neutron
Atomic weight
o Equals average mass of an element, including different isotopes in
proportion
o Very close to mass number of most common isotope
o Example:
Hydrogen atomic number = 1 (one proton)
Hydrogen atomic weight = 1.0079
o Not all hydrogen atoms have 0 neutrons
o 0.015 percent have 1 neutron (mass number 2)
o Lower percentage have 2 neutrons (mass number 3)
Elements
o Principal elements
Thirteen most abundant elements by body weight
o Trace elements
Fourteen other elements present in the body in very small
© 2015 Pearson Education, Inc.
, amounts
o All elements represented by a chemical symbol based on:
o English names (e.g., O for oxygen; C for carbon)
o Other language names (e.g., Na for sodium from Latin natrium)
Atoms are electrically neutral
o Every positive proton is balanced by a negative electron
o Electrons occupy an orderly series of energy levels within the electron
cloud
Can be diagrammed as series of concentric electron shells
First shell (closest to nucleus) is the lowest energy level
Number of electrons in outermost shell determines chemical
properties of element
Energy levels
o Outermost energy level (valence shell) is atom’s “surface”
o Atoms with unfilled outer shells are reactive
Tend to react with other atoms to fill outer shell
Examples: hydrogen, lithium
o Atoms with full outer shells are inert
Do not readily react with other atoms; more stable
Examples: helium, neon
o Called noble gases
Ions
o Atoms that have gained or lost electrons and are no longer electrically
neutral
o Losing an electron means:
Fewer electrons (negative) than protons (positive)
Net positive charge
Called a positive ion or cation
One missing electron charge of 1
More electrons missing more positive charge (e.g., 2, 3, 4)
Ions (continued)
o Gaining an electron means:
More electrons (negative) than protons (positive)
Net negative charge
Called a negative ion or anion
One extra electron charge of 1
More electrons gained more negative charge (e.g., 2, 3, 4)
o Stabilizing interactions often form chemical bonds
Chemical bonding creates
o Molecules (substances with two or more atoms)
o Compounds (substances with two or more different atoms)
Ionic bonds
o One of the most common types of chemical bonds
o Created by electrical attraction between cations (positive ions) and
anions (negative ions)
© 2015 Pearson Education, Inc.
