Chemical Basis of Life: Elements and Compounds

Chemical Substance

A material with definite chemical composition.

Element

Substance that cannot be broken down further.

Compound

Substance of two or more elements in fixed ratio.

Trace Element

Essential element required in minute amounts.

Fluoride

Trace element added to reduce tooth decay.

Atom

Smallest unit of matter retaining element properties.

Subatomic Particles

Protons, neutrons, and electrons in an atom.

Nucleus

Dense center of an atom containing protons and neutrons.

Atomic Number

Number of protons in an atom's nucleus.

Atomic Mass

Sum of protons and neutrons in nucleus.

Isotope

Atoms with same protons, different neutrons.

Carbon-14

Radioactive isotope used for carbon dating.

Radioactive Isotope

Unstable isotope that decays and releases energy.

Chemical Bond

Attraction between atoms due to electron interactions.

Electron Shell

Region around nucleus where electrons are found.

Goiter

Thyroid enlargement due to iodine deficiency.

Proton

Positively charged particle in an atom's nucleus.

Neutron

Neutral particle in an atom's nucleus.

Electron

Negatively charged particle orbiting the nucleus.

Mass Number

Total number of protons and neutrons.

PET Scan

Imaging technique using radioactive isotopes.

Chemical Properties

Characteristics determined by electron distribution.

Living Organisms

Composed of matter made from chemical elements.

Ionic Bond

Attraction between oppositely charged ions.

Ion

Atom or molecule with an electrical charge.

Covalent Bond

Atoms share electrons instead of transferring.

Valence Shell

Outer shell of an atom containing electrons.

Polar Covalent Bond

Unequal sharing of electrons between atoms.

Nonpolar Covalent Bond

Equal sharing of electrons due to similar electronegativity.

Hydrogen Bond

Weak bond between polar molecules, notably water.

Cohesion

Molecules of the same kind stick together.

Adhesion

Clinging of one substance to another.

Surface Tension

Measure of difficulty to break a liquid's surface.

Chemical Reaction

Process of making and breaking chemical bonds.

Reactants

Substances that undergo change in a chemical reaction.

Products

Substances formed as a result of a chemical reaction.

Electronegativity

Ability of an atom to attract electrons.

Water Molecule

Composed of two hydrogen and one oxygen atom.

Crystal of Table Salt

Ionic compound formed by sodium and chloride ions.

Thermal Energy

Energy associated with random movement of atoms.

Chemical Composition

Arrangement of atoms in a substance.

Molecule

Two or more atoms bonded together.

Cohesion in Water

Causes surface tension and droplet formation.

Hydrogen Bonding in Water

Enables water's unique properties and interactions.

Electron Transfer

Movement of electrons between atoms forming ionic bonds.

Polar Molecule

Molecule with an unequal distribution of charges.

Heat

Thermal energy transfer from warm to cool bodies.

Temperature

Measure of heat intensity in a substance.

Hydrogen Bonds

Strong interactions that stabilize water's temperature.

Evaporative Cooling

Cooling effect when a liquid evaporates.

Density of Ice

Ice is less dense than liquid water.

Aqueous Solutions

Uniform mixtures of water with solutes.

pH Scale

Measures acidity or basicity of a solution.

Acids

Substances that lower pH by adding H+ ions.

Buffers

Minimize pH changes by regulating H+ ions.

Chemical Elements

Fundamental substances essential for life.

Subatomic Particles

Protons, neutrons, and electrons in atoms.

Isotopes

Atoms with the same element but different mass.

Ionic Bonds

Electrostatic attraction between oppositely charged ions.

Covalent Bonds

Sharing of electron pairs between atoms.

Hydrogen Bonds

Weak attractions between polar molecules.

Chemical Reaction

Process that alters the composition of matter.

Polar Covalent Bonds

Unequal sharing of electrons between atoms.

Nonpolar Covalent Bonds

Equal sharing of electrons between atoms.

Reactivity of Elements

Determined by electron configuration and bonds.

Solvent of Life

Water's ability to dissolve many substances.

Life-Supporting Properties

Unique characteristics of water essential for life.