Matter and Its Forms

Definition and States of Matter

Matter is anything that occupies space and has mass. On Earth, matter exists in three primary physical states:

• Solid

• Liquid

• Gas

Elements and Compounds

• Element: A substance that cannot be broken down into other substances by ordinary chemical means. Each element is defined by its number of protons.

• Compound: A substance consisting of two or more different elements combined in a fixed ratio. Example: Table salt (sodium chloride, NaCl).

Trace Elements

Trace elements are present in minute quantities, making up less than 0.01% of human body weight. They are essential for life and include:

• Boron

• Chromium

• Cobalt

• Copper

• Fluorine

• Iodine

• Iron

• Manganese

• Molybdenum

• Selenium

• Silicon

• Tin

• Vanadium

• Zinc

Atomic Structure

Atoms and Subatomic Particles

An atom is the smallest unit of matter that retains the properties of an element. Atoms are composed of subatomic particles:

• Proton: Subatomic particle with a single positive charge (+).

• Electron: Subatomic particle with a single negative charge (−).

• Neutron: Electrically neutral subatomic particle (no charge).

The nucleus is the atom's central core, containing protons and neutrons.

Atomic Number, Mass Number, and Isotopes

• Atomic number: The number of protons in each atom of a particular element.

• Mass number: The sum of the number of protons and neutrons in an atom's nucleus.

• Atomic mass: Approximately equal to the mass number; the sum of protons and neutrons in daltons.

• Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.

• Radioactive isotope: An isotope in which the nucleus decays spontaneously, giving off particles and energy.

Chemical Bonds and Molecules

Types of Chemical Bonds

Chemical bonds are attractions between atoms resulting from sharing or transferring outer-shell electrons. The main types include:

• Ionic bond: Attraction between oppositely charged ions, formed when one atom transfers electrons to another.

• Covalent bond: Strong chemical bond in which two atoms share one or more pairs of valence electrons.

• Hydrogen bond: Weak chemical bond formed when a slightly positive hydrogen atom in a polar covalent bond is attracted to a slightly negative atom in another polar covalent bond.

Molecules and Electronegativity

• Molecule: Two or more atoms held together by covalent bonds.

• Electronegativity: A measure of an atom's attraction for shared electrons.

Types of Covalent Bonds

• Nonpolar covalent bond: Electrons are shared equally between two atoms of similar electronegativity.

• Polar covalent bond: Electrons are shared unequally between atoms that differ in electronegativity, resulting in partial charges.

Ions and Salts

• Ion: An atom or molecule with an electrical charge resulting from a gain or loss of one or more electrons.

• Salt: A synonym for an ionic compound.

Polar Molecules

• Polar molecule: Contains polar covalent bonds and has an unequal distribution of charges in different regions of the molecule.

Chemical Reactions

• Chemical reaction: The making and breaking of chemical bonds, leading to changes in the composition of matter.

• Reactant: A starting material in a chemical reaction.

• Product: The resulting material after a chemical reaction.

Properties of Water and Intermolecular Forces

Cohesion and Adhesion

• Cohesion: The sticking together of molecules of the same kind, often by hydrogen bonds.

• Adhesion: The attraction between different kinds of molecules.

Surface Tension

• Surface tension: A measure of how difficult it is to stretch or break the surface of a liquid, due to cohesive forces among molecules.

Thermal Energy, Heat, and Temperature

• Thermal energy: The energy associated with the random movement of atoms and molecules.

• Heat: The transfer of thermal energy from one body of matter to another.

• Temperature: A measure in degrees of the average thermal energy of the atoms and molecules in a body of matter.

Summary Table: Subatomic Particles

Key Equations

• Mass number:

• Atomic number:

Additional info:

• Understanding the structure of atoms and the nature of chemical bonds is fundamental to all biological processes, as these determine the properties of molecules essential for life.

• Water's unique properties, such as cohesion, adhesion, and surface tension, are critical for biological systems, including plant water transport and cellular processes.