Chemistry Chapter 3.1 Electron Theory

Matter and Elements

• Matter is anything that occupies space and has weight, e.g., air, water, clothing, animals, and the human body.
• Matter exists in three states: solid, liquid, and gaseous.
• An element is a substance that cannot be broken down into simpler substances, such as gold, silver, oxygen, and iron.
• Over 100 known elements combine to form various compounds encountered in daily life.
• Compounds are formed when one or more elements chemically combine (e.g., salt is sodium and chlorine, water is hydrogen and oxygen).

Structure of the Atom

• Atoms are the smallest particles that represent the characteristics of elements.
• Each atom is composed of electrons, protons, and sometimes neutrons, known as sub-atomic particles.
• The identity of an atom is determined by the number and arrangement of its sub-atomic particles.
• Protons have a positive charge, electrons have a negative charge, and neutrons are neutral, with protons being significantly more massive than electrons.
• The atomic nucleus contains protons and neutrons, while electrons orbit around the nucleus.
• Elements are classified by atomic number, which is the number of protons: hydrogen (atomic number 1) and helium (atomic number 2).
• Neutral atoms have an equal number of protons and electrons, resulting in no overall charge.

Molecules

• The smallest unit of a substance retaining its chemical properties is called a molecule.
• Molecules are composed of two or more atoms; elements can consist of identical atoms, such as a diatomic oxygen molecule (O₂).
• Compounds consist of different types of atoms, like a water molecule (H₂O) made of one oxygen and two hydrogen atoms.

Energy Levels

• Electrons occupy orbits around the nucleus, defined as shells that correspond to specific energy levels.
• Under normal conditions, electrons fill the lowest energy shell available.
• When energized, electrons can jump to higher energy shells; however, this state is temporary.
• As electrons return to their original shells, they release energy, illustrating the relationship between electron movement and energy.

Key Concepts

• Atoms and molecules are foundational to the diversity of matter in nature.
• The interaction and combination of sub-atomic particles dictate the properties and classifications of elements and compounds.
• Understanding atomic structure and energy dynamics provides insight into the behavior of matter on a molecular level.