Atoms, Bonds, and Water Molecules

Element

A pure substance where every single atom has the same number of protons.

Molecule

A group of two or more atoms held together by a chemical bond.

Compound

A mix of elements where proportions are fixed.

Nucleus

The center of the atom that contains all of an atom's mass.

Atomic Number

The number of protons in the nucleus that distinguishes one atom from another.

Electrons in a Neutral Atom

The number of protons and electrons are the same in an electrically neutral atom.

Orbitals

Concentric rings or regions surrounding the nucleus containing electrons.

2-8-8 Rule

The electron shell filling rule where the 1st shell has 2, 2nd has 8, and 3rd has 8 electrons.

Valence Shell

The outermost shell containing electrons; elements need 8 valence electrons to become stable.

Atomic Mass

The sum of protons plus neutrons in an atom.

Ionic Bonds

Bonds formed when one atom transfers electrons to another, creating oppositely charged ions.

Covalent Bonds

Bonds formed when two atoms share electrons because they have nearly full valence shells.

Hydrogen Bonds

An attraction between a partially positive Hydrogen atom and a strongly negative atom like oxygen, nitrogen, or fluoride.

Cation Formation

A metal atom loses one or more electrons to achieve stability, becoming positively charged.

Anion Formation

A nonmetal atom gains extra valence electrons to complete its outer shell, becoming negatively charged.

Polar Covalent Bond

A bond where one atom attracts electrons more strongly, resulting in unequal sharing.

Nonpolar Covalent Bond

A bond where atoms share electrons equally.

Polarity of Water

Oxygen pulls shared bond electrons closer, giving oxygen a partial negative charge and hydrogen a partial positive charge.

Water as a Universal Solvent

Charged poles allow water to pull apart and dissolve other polar substances and ionic compounds.

Water Molecule Structure

One central oxygen atom covalently bonded to two hydrogen atoms (H₂O).

Cohesion

The tendency of water molecules to stick to each other via hydrogen bonds.

Adhesion

The tendency of water molecules to stick to other polar surfaces.

High Specific Heat Capacity of Water

Allows water to absorb or release large amounts of heat with only a tiny change in temperature.

High Heat of Vaporization of Water

Requires substantial heat to change from a liquid to a gas, providing a cooling mechanism upon evaporation.

Lower Density of Ice

Water expands upon freezing, forming a rigid open lattice that makes solid ice less dense than liquid water.