Topic 1 Structure of Water and Hydrogen Bonding

Atomic number

The number of protons in the nucleus of an atom.

Atomic mass

The number of protons plus neutrons averaged over all isotopes

Element symbol

A one- or two-letter abbreviation used to represent an element.

Group

A vertical column in the periodic table; elements in the same group have the same number of valence electrons.

Period

A horizontal row in the periodic table; elements in the same period have the same number of electron shells.

Valence electrons

Electrons in the outermost electron shell that determine chemical reactivity.

Electron shell

A region around the nucleus where electrons reside; the number of shells relates to the period.

Octet rule

Atoms gain, lose, or share electrons to obtain a full valence shell of eight electrons.

Valence shell

The outermost electron shell of an atom.

Chemical bonds

Attractions between atoms formed by sharing or transferring valence electrons.

Electronegativity

A measure of an atom’s ability to attract electrons toward itself.

Covalent bond

A bond formed by sharing electrons between atoms, usually nonmetals.

Single bond

A covalent bond with one shared pair of electrons.

Double bond

A covalent bond with two shared pairs of electrons.

Triple bond

A covalent bond with three shared pairs of electrons.

Polar covalent bond

A covalent bond in which electrons are not shared equally, creating partial charges.

Nonpolar covalent bond

A covalent bond in which electrons are shared equally.

Ionic bond

A bond formed by transfer of electrons resulting in attraction between oppositely charged ions.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Ion

An atom or molecule with a net electrical charge due to loss or gain of electrons.

Hydrogen bond

A weak, intermolecular attraction between a partially positive hydrogen and a electronegative atom in another molecule.

Electronegative atom

An atom (e.g., O, N, F) that strongly attracts electrons.

Partial positive charge

A small positive charge on a hydrogen atom in a polar bond due to unequal sharing.

Partial negative charge

A small negative charge on the electronegative partner in a polar bond.

Polarity

The distribution of electrical charge within a molecule due to polar bonds. Created by an unequal sharing of electrons between oxygen and hydrogen within the molecule of water

Cohesion

Attraction between like molecules (e.g., water to water) due to hydrogen bonding.

Adhesion

Attraction of other molecules that are polar or have charge

Capillary action

Upward movement of water driven by cohesion, adhesion, and surface tension; occurs when adhesion exceeds cohesion.

Surface tension

The cohesive tendency of water at a surface, creating a 'skin' and high resistance to external forces.

Xylem

Plant tissue that transports water from roots to leaves.

Transpiration

Evaporation of water from leaves that drives water movement through the xylem.

Specific heat

The amount of heat required to raise the temperature of a substance; water has a high specific heat due to hydrogen bonding.

Heat of vaporization

The energy required to convert liquid water to vapor; water has a high heat of vaporization due to hydrogen bonds.

Evaporative cooling

Cooling effect when water evaporates and carries away heat.

Density

Mass per unit volume; ice is less dense than liquid water, so ice floats.

Solvent

The dissolving agent in a solution; water is a versatile solvent.

Solute

Substance dissolved in a solvent.

Solution

A homogeneous mixture of solute dissolved in solvent.

Like dissolves like

Substances with similar polarity dissolve in each other.

The partially negative oxygen in water will interact with a positive atom, The partially positive hydrogen in water will interact with a negative atom

Matter

Anything that takes up space and has mass.

Element

A substance that cannot be broken down into other substances by chemical reactions.

Compound

A substance consisting of two or more different elements combined in a fixed ratio.

H₂O

A compound composed of two hydrogen atoms and one oxygen atom; an example of a molecule of water.

NaCl

Sodium chloride; a compound formed from sodium (Na) and chlorine (Cl); common table salt.

Essential elements

Elements required for an organism’s survival and reproduction; about 20–25% of the naturally occurring elements are essential.

CHOPN

An acronym for essential elements that make up the majority of living matter; CHOPN are said to make up about 96% of living matter.

Trace elements

Elements required by an organism in very small quantities.