CHM209 Exam Questions With 100%
Correct Answers
isotopes - ANSWER -Atoms which have the same # protons but different # neutrons are
isotopes of the same element
-Isotopes have different masses but behave the same chemically
cation: - ANSWER positively charged ion; atom lost electron(s)
anion: - ANSWER negatively charged ion; atom gained electron(s)
covalent bond - ANSWER involves two atoms linked together through the sharing of two
electrons
the positively charged nuclei of both atoms are attracted to and pull on the two shared
electrons in the bond
this holds the two atoms together in a very strong interaction
In chemistry, purity refers to - ANSWER the extent to which something consists only one
chemical species (element or compound)
does water like to interact with many food molecules like sugars, proteins, and
carbohydrates?
Which molecules does it repulse?
These interactions/repulsions control the structures and properties of food - ANSWER
yes
fats and oils
Changes of state
ice cream - ANSWER liquid water -> ice
Changes of state
popcorn - ANSWER liquid water -> vapour
Changes of state
freeze dried fruit - ANSWER ice -> vapour
Changes of state
,Reduction (soups, sauces) - ANSWER liquid water -> vapour
What bond is water - ANSWER Covalent bonds (electrons are shared between two
atoms)
Polar bond (an uneven distribution of electrons in a covalent bond)
Electrons are localized more on the O than on the H's
What does higher electronegativity tell us?
On the periodic table it increases from left to right - ANSWER -stronger attraction for
electrons
-ability of an atom to attract shared electrons in a covalent bond toward itself
Non-polar covalent bonds - ANSWER between atoms with identical or similar EN,
difference of ≤0.5
C= 2.5, H = 2.1
• Polar covalent bonds - ANSWER - EN difference of 0.5-2
- C-N, C-O, N-H, O-H, C-Cl bonds - these are not ions!!!
Ionic bonds - ANSWER - EN difference > 2
- electrons are transferred between atoms
- Na+ Cl-
- makes ions with a full negative or positive charge
Hydrogen bond - ANSWER -The most important type of non-covalent interaction in
biological (food) molecules
-Much weaker than a covalent bond, but is strong among non-covalent attractions
Hydrogen bonds occur between which types of molecules - ANSWER Occurs between
the lone pair of a very electronegative element (i.e., nitrogen, oxygen) in one molecule,
and a hydrogen in another molecule that is bonded to a very electronegative element
(nitrogen, oxygen)
Hydrogen bonding occurs extensively in water• Every water molecule is H-bonded with
multiple other water molecules
On average how many? - ANSWER 3 H bonds per molecule
The polarity of molecules affects the solubility
- polar substances:
, - non-polar substances: - ANSWER - polar substances: soluble in polar solvents (e.g.
water)
-non-polar substances are insoluble in water but soluble in other non- polar solvents
In food molecules, the most common polar covalent bonds are C-O and H-O, also C-N,
and H-N.
What do polar molecules dissolve in? - ANSWER Polar solvents like water
With an increase in temperature is there an increase or decrease in average kinetic
energy of the system - ANSWER increased
Latent heat - ANSWER the "hidden" energy that needed to keep increasing the
temperature
Chemesthesis - ANSWER -detects chemical species that trigger sensations usually
associated with the sense of touch (e.g. temperature, pressure, pain)
- many species responsible for chemesthesis are irritants (but we can learn to enjoy
these sensations)
Double bonds - ANSWER Double bonds are simply two single covalent bonds that occur
between the same two atoms (2 sets of 2 shared electrons).
Each bond in a double bond counts toward the expected number of bonds on an atom by
the HONC rule.
for ex. All C's have 4 bonds and no lone pairs.
To determine formal charge: - ANSWER -count all non-bonding (lone pair) electrons
-count 1 electron from each covalent bond around the atom
-add the above; if this number = # valence electrons in neutral atom, the formal charge is
0
-if number < # valence electrons, the difference gives the value of positive (+) formal
charge
if number > # valence electrons, the difference gives the value of negative (-) formal
charge
Drawing Organic Molecules - ANSWER Three general rules:
-Carbon atoms are not usually shown.
-Hydrogen atoms bonded to carbon are not shown, assume enough hydrogens are
attached to each carbon to satisfy the number of bonds needed by carbon.
-Any atom other than carbon and hydrogen are shown, called "heteroatoms"
Correct Answers
isotopes - ANSWER -Atoms which have the same # protons but different # neutrons are
isotopes of the same element
-Isotopes have different masses but behave the same chemically
cation: - ANSWER positively charged ion; atom lost electron(s)
anion: - ANSWER negatively charged ion; atom gained electron(s)
covalent bond - ANSWER involves two atoms linked together through the sharing of two
electrons
the positively charged nuclei of both atoms are attracted to and pull on the two shared
electrons in the bond
this holds the two atoms together in a very strong interaction
In chemistry, purity refers to - ANSWER the extent to which something consists only one
chemical species (element or compound)
does water like to interact with many food molecules like sugars, proteins, and
carbohydrates?
Which molecules does it repulse?
These interactions/repulsions control the structures and properties of food - ANSWER
yes
fats and oils
Changes of state
ice cream - ANSWER liquid water -> ice
Changes of state
popcorn - ANSWER liquid water -> vapour
Changes of state
freeze dried fruit - ANSWER ice -> vapour
Changes of state
,Reduction (soups, sauces) - ANSWER liquid water -> vapour
What bond is water - ANSWER Covalent bonds (electrons are shared between two
atoms)
Polar bond (an uneven distribution of electrons in a covalent bond)
Electrons are localized more on the O than on the H's
What does higher electronegativity tell us?
On the periodic table it increases from left to right - ANSWER -stronger attraction for
electrons
-ability of an atom to attract shared electrons in a covalent bond toward itself
Non-polar covalent bonds - ANSWER between atoms with identical or similar EN,
difference of ≤0.5
C= 2.5, H = 2.1
• Polar covalent bonds - ANSWER - EN difference of 0.5-2
- C-N, C-O, N-H, O-H, C-Cl bonds - these are not ions!!!
Ionic bonds - ANSWER - EN difference > 2
- electrons are transferred between atoms
- Na+ Cl-
- makes ions with a full negative or positive charge
Hydrogen bond - ANSWER -The most important type of non-covalent interaction in
biological (food) molecules
-Much weaker than a covalent bond, but is strong among non-covalent attractions
Hydrogen bonds occur between which types of molecules - ANSWER Occurs between
the lone pair of a very electronegative element (i.e., nitrogen, oxygen) in one molecule,
and a hydrogen in another molecule that is bonded to a very electronegative element
(nitrogen, oxygen)
Hydrogen bonding occurs extensively in water• Every water molecule is H-bonded with
multiple other water molecules
On average how many? - ANSWER 3 H bonds per molecule
The polarity of molecules affects the solubility
- polar substances:
, - non-polar substances: - ANSWER - polar substances: soluble in polar solvents (e.g.
water)
-non-polar substances are insoluble in water but soluble in other non- polar solvents
In food molecules, the most common polar covalent bonds are C-O and H-O, also C-N,
and H-N.
What do polar molecules dissolve in? - ANSWER Polar solvents like water
With an increase in temperature is there an increase or decrease in average kinetic
energy of the system - ANSWER increased
Latent heat - ANSWER the "hidden" energy that needed to keep increasing the
temperature
Chemesthesis - ANSWER -detects chemical species that trigger sensations usually
associated with the sense of touch (e.g. temperature, pressure, pain)
- many species responsible for chemesthesis are irritants (but we can learn to enjoy
these sensations)
Double bonds - ANSWER Double bonds are simply two single covalent bonds that occur
between the same two atoms (2 sets of 2 shared electrons).
Each bond in a double bond counts toward the expected number of bonds on an atom by
the HONC rule.
for ex. All C's have 4 bonds and no lone pairs.
To determine formal charge: - ANSWER -count all non-bonding (lone pair) electrons
-count 1 electron from each covalent bond around the atom
-add the above; if this number = # valence electrons in neutral atom, the formal charge is
0
-if number < # valence electrons, the difference gives the value of positive (+) formal
charge
if number > # valence electrons, the difference gives the value of negative (-) formal
charge
Drawing Organic Molecules - ANSWER Three general rules:
-Carbon atoms are not usually shown.
-Hydrogen atoms bonded to carbon are not shown, assume enough hydrogens are
attached to each carbon to satisfy the number of bonds needed by carbon.
-Any atom other than carbon and hydrogen are shown, called "heteroatoms"
