Chemical Bonds Flashcards
(27 cards)
What distinguishes a molecule from a compound?
A molecule is two or more atoms held by covalent bonds; if those atoms are different elements in a fixed ratio, the molecule is also a compound.
What is the atomic number?
The number of protons in an atom’s nucleus.
What is the mass number?
Total protons + neutrons in the nucleus.
Why are atoms with full valence shells chemically inert?
A complete valence shell makes them stable; they have no tendency to gain, lose, or share electrons.
How many valence electrons does carbon have?
Four.
How many additional electrons does oxygen need to fill its valence shell?
Two.
Define electronegativity.
An atom’s attraction for shared electrons in a covalent bond.
Describe a non‑polar covalent bond.
Electrons are shared equally because the atoms have similar electronegativity.
Describe a polar covalent bond.
Electrons are shared unequally; they spend more time near the more electronegative atom, creating partial charges.
Give the definition of a hydrogen bond.
A weak attraction between a slightly positive H (in a polar bond) and a slightly negative atom (often O or N) on another molecule.
List four life‑supporting properties of water explained by hydrogen bonding.
Cohesion, temperature moderation (high specific heat & evaporative cooling), lower density of ice vs. liquid, and excellent solvent ability.
Define cohesion vs. adhesion.
Cohesion: attraction between like molecules; Adhesion: attraction between different kinds of molecules.
Why does ice float on liquid water?
Hydrogen bonds stabilize into a lattice in ice, making it less dense than liquid water.
What is surface tension?
The difficulty of breaking the surface of a liquid; water’s is high due to cohesion.
Name the seven functional groups essential in biology.
Hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, methyl.
Which group is characteristic of alcohols and is polar?
Hydroxyl (‑OH).
What functional group acts as an acid by donating H⁺?
Carboxyl (‑COOH).
Which group acts as a base by accepting H⁺?
Amino (‑NH₂).
What is the key property of the phosphate group in molecules like ATP?
Contributes negative charge and can release energy when reacting with water.
How do two sulfhydryl (‑SH) groups help stabilize proteins?
They form covalent disulfide bridges upon oxidation.
What is the effect of adding a methyl group to DNA?
Can alter gene expression (epigenetic regulation).
In H₂O, which atom carries a partial negative charge and why?
Oxygen, because it is more electronegative and pulls shared electrons closer.
Are the H–C bonds in methane polar or non‑polar?
Non‑polar (similar electronegativity).
What type of bond forms between Na⁺ and Cl⁻ in table salt?
Ionic bond.
