Topic 2 - The Nature Of Molecules And Water Flashcards
Atom
The smallest unit of matter that has the properties of an element
Isotope
One or more forms of an element that have a different number of neutrons
Atomic number
Number of protons
Mass number
Protons + neutrons
Where are the protons and neutrons located in an atom?
In the nucleus
Where are the electrons located in an atom?
In orbitals/clouds around the nucleus
True or false: in a neutral atom, protons = electrons
True
What determines the chemical behavior of atoms?
Electrons
What is the octet rule?
Atoms are most stable if their valence shell is full of electrons.
When is an atom reactive?
When it does not have the maximum number of electrons in its energy level.
Electronegativity
The tendency of an atom to attract electrons towards itself.
True or false: oxygen has the highest electronegativity
True
List the electronegativities of the following elements: O, N, C, H
O: 3.5
N: 3.0
C: 2.5
H: 2.1
Ionic bond
The attraction of 2 oppositely charged ions; a bond in which electrons are transferred from one ion to the other
Ions
Atoms that have an unequal number of protons and electrons
Cations
Positively charged ions
True or false: cations lose electron(s)
True
Anions
Negatively charged ions
True or false: anions gain electron(s)
True
Ionic bonds are strong as a crystal, but weak in water. Why?
Water is polar and interferes with the electrical charge holding ions together.
Covalent bonds
Bonds between two atoms sharing electrons
True or false: covalent bonds are strong bonds
True
What is the strongest type of covalent bond?
Triple bond
Polar covalent bond
Type of covalent bond that forms as a result of unequal electron sharing, resulting in creating slightly positive and negative charged molecule regions.
In other words, polarity is caused by atoms with different electronegativities sharing electrons in a covalent bond.
Intramolecular
Is a polar covalent bond intramolecular or intermolecular?
Intramolecular
Hydrogen bonds
Bonds that occur between two molecules that have polar covalent bonds.
The slightly positively charged atom (hydrogen) in one polar covalent bond is attracted to the slightly negatively charged atom in a second polar covalent bond.
Intermolecular
Are hydrogen bonds strong or weak?
Weak
Why are hydrogen bonds biologically important?
They can be easily broken and reform.
1. They hold proteins together at secondary and tertiary structure, allowing them to be flexible.
2. They hold the strands of DNA together in the double stranded helix, allowing it to break apart and reform easily for replication or protein synthesis.
3. They hold water together, essential for all life.
Van der Waals interactions
Fleeting interactions between atoms due to the movement of electrons
List bonds from strongest to weakest
Covalent, polar covalent, ionic, hydrogen, van der Waals
Why is water a unique substance?
Its polarity and hydrogen bonding give it special properties that tie to the processes of life.
What are the special properties of water?
High heat capacity, high heat of vaporization, ability to dissolve polar molecules (solvent), cohesion and adhesion, and dissociation into ions that generates pH
True or false: all the properties of water are due to its polarity.
True
Explain how water is polar and why it forms hydrogen bonds.
The hydrogen and oxygen within water form polar covalent bonds. Water molecules attract other water molecules (also polar covalent), creating hydrogen bonds.
Hydrophilic
“Water loving”
Polar substances that interact readily with or dissolve in water
Hydrophobic
“Water fearing”
Nonpolar substances that do not interact well with water
Water’s high heat capacity
Water has a high specific heat, meaning it can absorb or release a large amount of heat with only a slight change in its own temperature. It has the highest heat capacity of any liquid.
Heat
The measure of the total amount of kinetic energy due to molecular motion
Temperature
The intensity of heat due to the average kinetic energy of molecules
Kinetic energy
The energy of motion
Water’s high heat of vaporization
Water has a high heat of vaporization, the amount of energy required to change one gram of liquid to a gas.
Explain why water’s high specific heat is biologically important.
- Moderated temperature of organisms
- Moderated global temperatures
- Evaporative cooling
True or false: water acts as a heat sink/reservoir.
True
Why is water less dense in its solid form?
When water cools, water molecules lose kinetic energy. Hydrogen bonds become more stable, trapping pockets of air between water molecules.
True or false: water molecules push farther apart when water freezes and form a lattice structure.
True
Solvent
A substance capable of dissolving other polar molecules and ionic compounds; the dissolving agent of a solution
Solution
A liquid that is a mixture of substances
Solute
Substance that is dissolved
Why is water a versatile solvent?
Its polarity allows it to form hydrogen bonds with other polar (hydrophilic) substances easily. This allows water to dissolve these substances, facilitating their transport and interaction with other polar molecules (i.e. chemical reactions.)
True or false: nonpolar substances do not mix well with water
True. Nonpolar substances are hydrophobic.
Cohesion
Water molecules are attracted to each other because of hydrogen bonding
Adhesion
The attraction between water molecules and other molecules
Surface tension
The capacity of a substance to withstand rupturing when placed under tension or stress
Why are cohesion and adhesion biologically important?
They help the transport of water through xylem against gravity in plants via capillary action.
pH
“potential of hydrogen”
The measure of [H+] in a solution
Hydrogen ion
H+
Hydronium ion
H3O+
Hydroxide ion
OH-
Acid
Any substance that increases the H+ concentration of a solution
Base
Any substance that reduces the H+ concentration of a solution
True or false: as [H+] increases, [OH-] decreases, and vice versa
True
How is pH calculated?
pH is calculated as the negative of the base 10 logarithm of the concentration of H+
Ex. log10 of 1 x 10^-7 moles/liter of H+ is -7. The negative of this number yields a pH of 7.
Where on the pH scale are acids
<7 pH
Where on the pH scale are bases
> 7 pH
True or false: pure (distilled water) is neutral at a pH of 7
True
True or false: most living cells remain close to pH 7
True
True or false: human blood has a pH of 7.4, making it slightly basic; changes to 7.1 or 7.7 are fatal
True
Buffers
Substances that minimize changes in concentrations of H+ and OH- in a solution. Most buffers consist of an acid-base pair that reversibly combines with H+
What is the key buffer in human blood?
The acid-base pair of carbonic acid (H2CO3) and bicarbonate (HCO3-)
Explain how human blood is maintained at a narrow pH.
Water combines with carbon dioxide in the blood to produce carbonic acid, which then becomes a bicarbonate ion and H+. If the blood becomes too basic, carbonic acid will form making the blood more acidic. If the blood becomes too acidic, bicarbonate will form making the blood more basic.
Show the carbonic acid-bicarbonate buffer system.
CO2 + H2O ⇌ H2CO3 ⇌ HCO3- + H+
Explain how an increase in atmospheric CO2 leads to the acidification of oceans.
CO2 + H2O ⇌ H2CO3 (carbonic acid)
