Chapters 22, 2, 3 Flashcards
What is an Isotope?
Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element:
PROTON
Positively charged in the nucleus
What is the mass number of an ion with 109 electrons, 158 neutrons, and a +1 charge?
268
An ionic bond is formed when __________
one atom transfers an electron to another atom.
A carbon atom and a hydrogen atom form what type of bond in a molecule?
nonpolar covalent bond
Note:
Covalent bond : That carbon shares its outer valence electrons with up to four hydrogens. This completes both of their outer shells making them stable. The C−H bond is very strong, it is relatively unreactive.
Atoms with similar electronegativities form nonpolar covalent bonds.
A substance that cannot be broken down into other substances by ordinary chemical procedures is a(n) _______________________
Element
Note: This is the definition of an element.
What is a covalent bond?
Sharing of a pair of outer-shell electrons by two atoms.
Example: Two hydrogen atoms share electrons to complete their first outer shell that can hold a total of two electrons.
What is a Molecule?
Two or more atoms held together by a covalent bond
What is a double covalent bond?
Sharing of TWO pairs of outer-shell electrons by two atoms.
What is an atom?
Covalent bonds hold atoms together because they ___________________
(a) fill shells without giving atoms much charge.
(b) bring electrons closer to protons.
By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom’s charge stay close to zero?
Oxygen keeps 6 electrons to itself. The 4 shared electrons migrate between O and the other atoms, thus contributing 4 half-charges to oxygen. This gives oxygen about 8 units of negative charge, balancing the atom’s 8 protons.
Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds known as _____
hydrogen bonds
Note:
The polarity of a water molecule allows the oxygen of one water molecule to bond weakly to the hydrogen of another water molecule.
why does water have a high specific heat?
Water molecules can make 4 hydrogen bonds.
When you heat water, much of the heat is used to break hydrogen bonds. Only the remaining heat can increase molecular motion, raising the temperature.
What is a buffer?
A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added.
In this fashion, buffers minimize the change in the pH of a solution
electronegativity
The tendency of an atom to pull electrons toward itself
Which bond is the weakest?
Hydrogen Bonds are weaker than covalent bonds because they do not involve sharing of electrons, and they are weaker than ionic bonds because they involve the attraction of partial (not full) opposite charges.
neutral solution
hydrogen ions is equal to the concentration of hydroxide ions
Measurements show that the pH
of a particular lake is 4.0. What is the hydrogen ion concentration of the lake?
10^−4M
Specific heat of water
The table shown here lists the specific heat of several substances.
Substance Specific heat J/g/∘C
water 4.18
ethyl alcohol 2.44
benzene 1.80
sulfuric acid 1.40
Which answers are true?
1) Sulfuric acid is less resistant to temperature change than
water.
2) Ethyl alcohol likely exhibits more hydrogen bonding than
water.
3) Benzene is more resistant to temperature change than
sulfuric acid.
4) Water has a high specific heat due to the hydrogen bonding
between water molecules.
5) More heat is required to raise the temperature of 1 g of
benzene 1∘C than to raise the temperature of 1 g of water
1∘C.
6) More heat is required to raise the temperature of 1 g of
water 1∘C than to raise the temperature of 1 g of ethyl
alcohol 1 ∘C.
7) Water is less resistant to temperature change than ethyl
alcohol.
Answers: 1,3,4,6
Note;
Water has a high specific heat relative to other substances due to the hydrogen bonding that occurs between water molecules.
Water is very resistant to temperature increases because the hydrogen bonds between the water molecules must be disrupted to raise the temperature of the water.
By the same token, water must lose a large amount of heat and form many additional hydrogen bonds for its temperature to decrease.
Water’s high specific heat has some important consequences for life on Earth. For example, coastal areas generally have milder climates than inland areas due to the oceans’ high specific heat.
Oceans are able to absorb a large amount of heat during the daytime and summer, keeping air temperatures relatively cool. At night and during the winter, the oceans cool gradually, releasing heat and warming the air.
Water’s high specific heat also stabilizes ocean temperatures, resulting in a favorable environment for marine life.
What are hydrogen bonds?
Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds
Polar attractions are _______________
(a) forces between atoms with partial charges.
(b) weaker than covalent bonds.
(c) important because they are numerous.
(a) and (b) are true. (c) is false.
(a), (b), and (c) are correct.
Last one a,b,c are correct
A pH of 6 is how many times more acidic than a pH of 9?
A pH of 6 is 10 times more acidic than 7, which is 10 times more acidic than 8, which is 10 times more acidic than 9. 10 × 10 × 10 ≡ 1,000.
The partial charges on a water molecule occur because of ______________
Answer:
the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule
Notes:
The partial changes on a water molecule occur because of the unequal sharing of electrons between the hydrogen and oxygen atoms of the water molecule.
Atoms in a molecule attract shared electrons to varying degrees, depending on the element. The attraction of a particular atom for the electrons of a covalent bond is called its electronegativity. The more electronegative an atom is, the more strongly it pulls shared electrons toward itself. Oxygen is one of the most electronegative of all the elements, attracting shared electrons much more strongly than hydrogen does. In a covalent bond between oxygen and hydrogen, the electrons spend more time near the oxygen nucleus than they do near the hydrogen nucleus. Because electrons have a negative charge and are pulled toward oxygen in a water molecule, the oxygen atom has a partial negative charge (indicated by the Greek letter δ with a minus sign, δ–, or “delta minus”), and each hydrogen atom has a partial positive charge (δ+, or “delta plus”). Because the oxygen atom in the water molecule is more electronegative than the hydrogen atoms the oxygen, the electrons of the bond are not shared equally. This type of bond is called a polar covalent bond.
“The achievement of a stable configuration by one atom of a bond but not by the other partner” is not correct because the entire water molecule is stabilized by covalent bonds joining the oxygen to the two hydrogen atoms, but because oxygen is highly electronegative a polar molecule is formed.
“Covalent bonding” is not correct because oxygen is highly electronegative forming a polar molecule.
“Widespread ionization” is not correct because the molecule is stabilized by polar covalent interactions. However, the partial charges on a water molecule contribute to its ability to dissociate.
“The high electronegativity of hydrogen” is not correct because hydrogen is not a highly electronegative element.
You can fill a glass of water to just slightly above the rim without it spilling over the glass. What property of water best explains this phenomenon?
Surface tension
Note:
You can fill a glass of water to just slightly above the rim without it spilling over the glass. The property of water best explains this phenomenon is surface tension.
Surface tension is a measure of how difficult it is to stretch or break the surface of a liquid. Water has a greater surface tension than most other liquids. At the interface between water and air is an ordered arrangement of water molecules, hydrogen-bonded to one another and to the water below. This makes the water behave as though coated with an invisible film. You can observe the surface tension of water by slightly overfilling a drinking glass; the water will stand above the rim. In a more biological example, some animals can stand, walk, or run on water without breaking the surface. This is the correct answer.
“Adhesion” is incorrect because this is the attraction of unlike substances.
“Its polarity” is incorrect because although the property that is responsible for this phenomenon is a result of the polarity of water molecules, is a better answer.
“Evaporative cooling” is not correct because evaporative cooling is the cooling of a liquid’s surface as some of the liquid evaporates.
A substance that reduces the hydrogen ion concentration of a solution is __________.
buffer
Note:
A substance that reduces the hydrogen ion concentration of a solution is called a base.
When bases dissolve in water, they donate additional OH+ to the solution, thereby increasing the hydroxyl ion concentration of a solution. For example, when sodium (NaOH) is added to water, hydroxyl ions dissociate from sodium ions: NaOH Na+ + OH– . This source of OH– (dissociation of water is the other source) results in an alkaline or basic solution—one having more OH– than H+.
“An acid” is incorrect because these are substances that increase the concentration of H+ in a solution.
“A buffer” is incorrect because buffers are substances that minimize changes in the concentration of H+ and OH– in a solution.
“Neutral” is incorrect because neutral substances have an equal concentration of H+ and OH– in a solution.
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A substance that reduces the hydrogen ion concentration of a solution is __________.
buffer
Note:
A substance that reduces the hydrogen ion concentration of a solution is called a base.
When bases dissolve in water, they donate additional OH+ to the solution, thereby increasing the hydroxyl ion concentration of a solution. For example, when sodium (NaOH) is added to water, hydroxyl ions dissociate from sodium ions: NaOH Na+ + OH– . This source of OH– (dissociation of water is the other source) results in an alkaline or basic solution—one having more OH– than H+.
“An acid” is incorrect because these are substances that increase the concentration of H+ in a solution.
“A buffer” is incorrect because buffers are substances that minimize changes in the concentration of H+ and OH– in a solution.
“Neutral” is incorrect because neutral substances have an equal concentration of H+ and OH– in a solution.
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Hydrophilic molecules __________.
are charged molecules that are attracted to the partial charge of the water molecule
Note:
Hydrophilic molecules are charged molecules that are attracted to the partial charge of the water molecule.
Any substance that has an affinity for water is said to be hydrophilic (from the Greek hydro, water, and philos, loving). In some cases, substances can be hydrophilic without actually dissolving. For example, some molecules in cells are so large that they do not dissolve. Another example of a hydrophilic substance that does not dissolve is cotton, a plant product. Cotton consists of giant molecules of cellulose, a compound with numerous regions of partial positive and partial negative charges that can form hydrogen bonds with water. Water adheres to the cellulose fibers. Thus, a cotton towel does a great job of drying the body, yet it does not dissolve in the washing machine. Cellulose is also present in the walls of water-conducting cells in a plant; the adhesion of water to these hydrophilic walls helps water move up the plant against gravity.
A water-soluble protein
“Are polar molecules that are attracted to the nonpolar portion of the water molecule” is incorrect because the water molecule is polar and charged.
“Are uncharged, nonionic substances that repel water” is incorrect because this describes hydrophobic molecules.
“Are nonionic molecules that are attracted to the nonpolar portion of the water molecule” is incorrect because hydrophilic molecules are charged and interact with the polar water molecule.
“Never have a partial charge at one end of the molecule” is incorrect because in order for a hydrophilic molecule to interact with water, it must have a charge.
