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Chapter 2

Chapter Notes for Chapter 2 of Human Physiology 5e

Biological Sciences
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Human Physiology (Fifth Edition)
Silverthorn, D. U.
Chapter 2 Molecular Interactions
Chemistry Review
Atoms: building blocks of all matter, composed of protons (+ charge), electrons (-
charge), and neutrons (uncharged), most of an atoms volume is empty space
The protons and neutrons of the atom are clustered in the nucleus, electrons,
which are held in their orbits by their attraction to the protons, are contained in
the space around the nucleus
The Number of Protons in the Nucleus Determines the Element
oElement: simplest type of matter
oAtomic number of an atom is the number of protons in the nucleus, which
specifies what element the atom is
oOxygen, carbon, and hydrogen make up more than 90% of the body’s mass
oMajor essential elements of the body: oxygen, carbon, hydrogen, nitrogen,
phosphorus, sodium, potassium, calcium, magnesium, sulfur and chlorine
oThe body also requires trace amounts of other elements (i.e. selenium)
oAtomic mass: total mass of protons and neutrons in the atom
oElectrons are very light in comparison to protons and neutrons (1836
electrons = one neutron)
Isotopes of an Element Contain Different Numbers of Neutrons
onumber of protons in an element is constant
oisotopes: atoms of an element that have different numbers of neutrons,
isotopes of a particular element have the same chemical properties (which
depend on electron configuration, not proton numbers)
oradioisotopes: unstable isotopes that emit radiation (alpha, beta, gamma)
Electrons Form Bonds Between Atoms and Capture Energy
oArrangement of electrons in the outermost shell determines its binding
oCovalent bonds: atom bonding through electron sharing
oIons: atoms with an electric charge because of gain/loss of electron(s)
oHigh-energy electrons: electrons able to capture and transfer energy from
their environment for synthesis, movement, other life processes
oFree radicals: atoms with at least one unpaired electron who will try to
steal an electron in order to become more stable, thought to contribute to
aging and certain diseases
chain of free radical production disrupts cell function
oAntioxidants: substances that prevent damage to our cells by giving up
electrons without becoming a free radical
Molecular Bonds and Shapes
Molecules: two or more atoms linked by sharing electrons, most molecules are
compounds (contain more than one element)
Bonds: transfer or sharing of electrons between atoms

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oStrong bonds: covalent, ionic
oWeak bonds: hydrogen, Van der Waals
Covalent Bonds are Formed When Adjacent Atoms Share Electrons
oMost of the bonds within molecules are covalent
oCovalent bonds need energy in order to be broken apart
oThe number of unpaired electrons in an atoms outermost shell
indicates how many covalent bonds it can make
oEach shared electron pair represents a single covalent bond
oDouble bond: two electron pairs are shared between adjacent atoms
oPolar and Nonpolar Molecules
Electron pairs in covalent bonds are not always shared evenly
When there is uneven sharing, the atom with the stronger
electron attraction gains a slightly negative charge, and the
atom with the weaker attraction becomes slightly positive =
polar molecules (molecules with regions of partial
positive/negative charge that are said to have positive and
negative poles)
Hydrophilic: water-loving; dissolve easily
Nonpolar molecule: molecule with evenly shared electrons
Hydrophobic: water-hating; do not dissolve well
Ionic Bonds Form When Atoms Gain or Lose Electrons
oIonic bond: transfer of electron from one atom to another; an atom has
such a strong attraction for electrons that it pulls them away from
another atom
oPolar regions of molecules (such as water) are able to disrupt ionic
bonds and cause some molecules to dissolve
Hydrogen Bonds and Van der Waals Forces Are Weak Interactions
Between Atoms
oHydrogen bond: weak attractive force between a hydrogen and nearby
oxygen/nitrogen/fluorine atom
Occur between neighboring molecules or between atoms in
different parts of the same molecule
oSurface tension: (of water) attractive force that causes water to form
spherical droplets or to bead up when spilled on nonabsorbent
surfaces caused by hydrogen bonding between water molecules
oVan der Waals forces (VdW): weak, nonspecific attractions between the
nucleus of any atom and the electrons of nearby aroms
Atoms attracted by VdW keep moving closer together until they
Allows atoms to pack closely together to occupy minimum space
Individually weak, but strong as a group
Molecular Shape is Related to Molecular Function
oWeak bonds between atoms create noncovalent interactions that
influence molecular shape
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