02/12 02 Chemistry of Life Free Online FlashCards

What does an element’s atomic number identify?

The atomic number is the number of protons in an atom’s nucleus, and it identifies the element.

What distinguishes isotopes of the same element?

Isotopes are atoms of the same element that have different numbers of neutrons. Some radioactive isotopes are useful in imaging, tracing, and age determination.

Why is carbon especially important in biological molecules?

Carbon can form four stable covalent bonds, allowing it to serve as the structural framework for complex organic molecules.

What makes a covalent bond polar?

A polar covalent bond shares electrons unequally because one atom attracts them more strongly. In water, oxygen has a partial negative charge and hydrogen has a partial positive charge.

What is the hydrophobic effect?

The hydrophobic effect causes nonpolar groups to cluster in water, reducing their contact with water. It helps form membranes, protein interiors, lipid droplets, and binding sites.

How do dehydration synthesis and hydrolysis differ?

Dehydration synthesis joins smaller molecules by forming a covalent bond and removing H₂O. Hydrolysis adds H₂O to break a covalent bond.

What are oxidation and reduction?

Oxidation is the loss of electrons, whereas reduction is the gain of electrons. They always occur together in redox reactions.

How does a catalyst affect a chemical reaction?

A catalyst speeds a reaction by lowering its activation energy without being consumed. Enzymes are biological catalysts that bind particular reactants.

How do cohesion and adhesion differ?

Cohesion is attraction between water molecules; adhesion is attraction between water and other substances. Together, they contribute to capillary action.

Why does ice float on liquid water?

Ice is less dense than liquid water because hydrogen bonds hold its molecules in an open lattice. Therefore, ice floats and can insulate water below it.

What does the pH scale measure?

pH is the negative base-10 logarithm of hydrogen-ion concentration: pH = −log₁₀[H⁺]. A one-unit decrease in pH represents ten times more H⁺.

How does a buffer resist changes in pH?

A buffer minimizes pH changes by reversibly accepting or donating hydrogen ions. Biological buffers usually contain a weak acid and its conjugate base.