Atomic Structure and Chemistry Basics

Atomic Structure

• Subatomic particles in an atom's nucleus are protons and neutrons.
• Neutrons have a mass of 1 amu and no charge.
• All atoms of a given element have the same atomic number.
• The majority of an atom's mass comes from neutrons and protons.
• The atomic mass of an atom is measured in atomic mass units based on ¹²C.

Energy Levels and Electron Configuration

• The electrons in the first energy level of an atom possess the least amount of energy.
• The maximum number of electrons that can occupy the second energy level is 8.
• When energy is absorbed, electrons move to higher energy levels, and when energy is released, they move to lower energy levels.
• The bright-line spectrum of an element is produced when energy is released as electrons move to lower energy levels.

Periodic Table and Elements

• Elements are arranged in the Periodic Table in order of increasing atomic number.
• The element with chemical properties most similar to sodium is lithium.
• Alkali metals, such as Na, are found in Group 1.
• The group that contains elements composed of diatomic molecules is Group 17.
• A sample of an element that is malleable and can conduct electricity could be Sn.
• Nonmetallic solids are often brittle.

Chemical Bonding

• In an ionic bond, electrons are transferred from a metal to a non-metal.
• In a covalent bond, electrons are shared between two atoms.
• Ionic compounds typically have high melting and boiling points, conduct electricity, and are soluble in water.
• Covalent compounds usually have lower melting and boiling points, do not conduct electricity, and are often not soluble in water.

Chemical Reactions and Stoichiometry

• A balanced equation for the reaction of potassium with water is 2K + 2H₂O → 2KOH + H₂.
• A balanced equation for the reaction of aluminum with bromine is 2Al + 3Br₂ → 2AlBr₃.
• Combinations that are definitely chemical changes include those with observable evidence such as gas production, temperature change, or the formation of a precipitate.
• The molar mass of a compound is calculated based on the atomic masses of its constituent elements.
• The number of moles of a substance can be calculated using its molar mass and Avogadro's number.