Learn: Atoms, Water, and Carbon

Element

A pure substance that cannot be broken down into simpler substances.

Atom

The smallest unit of an element, composed of protons, neutrons, and electrons.

Valence Electrons

Electrons in the outermost energy level that determine an atom's chemical properties and reactivity.

Ion

A charged particle created by the addition or removal of electrons.

Anion

A negatively charged ion formed by gaining an electron.

Cation

A positively charged ion formed by losing an electron.

Ionic Bonding

Chemical attractions between atoms that completely gain or lose electrons.

Covalent Bonding

A chemical bond formed when atoms share valence electrons.

Polar vs. Nonpolar Covalent Bonds

Polar bonds involve unequal electron sharing due to electronegativity differences; nonpolar involve roughly equal sharing.

Electronegativity

An atom's ability to attract shared electrons towards itself.

Polarity of Water

Oxygen attracts shared electrons more strongly than hydrogen, creating a partial negative charge near oxygen and partial positive charges near hydrogens.

Hydrogen Bond

A force that occurs when a hydrogen atom is sandwiched between two strongly electronegative atoms (typically N, O, or F).

Ice Lattice Density

Ice is less dense than liquid water because its molecules are far apart and uniformly arranged in a rigid lattice.

High Specific Heat of Water

Water takes a lot of energy to raise in temperature, providing a stable environment for life due to hydrogen bonding.

Cohesion and Adhesion in Water

Cohesion is water molecules sticking to each other via hydrogen bonds; adhesion is water sticking to other surfaces.

Why Carbon over Silicon for Life?

Carbon is smaller, forms stronger C-C bonds, holds electrons closer to the nucleus, and forms up to four stable covalent bonds.

Four Major Families of Small Organic Molecules

Proteins, nucleic acids, lipids, and carbohydrates.

General Formula of Carbohydrates

(CH2O)n

Glycosidic Bond

A covalent bond that joins one sugar to another, formed through a dehydration reaction that releases H2O.

Aldose vs. Ketose Sugars

Aldoses have a carbonyl group at the end of the carbon chain; ketoses have it within the carbon chain.

Starch vs. Glycogen

Starch serves as energy storage in plants, while glycogen serves as energy storage in animals.

Cellulose and Chitin

Cellulose provides structural support in plants, and chitin provides structural support in fungi and arthropods.