Chemistry Atomic Structure and Periodic Table

Atomic Structure

• Atoms are the fundamental building blocks of matter.
• Atoms consist of a nucleus containing protons (positively charged) and neutrons (neutral).
• Electrons (negatively charged) orbit the nucleus in shells or energy levels.
• The number of protons defines the element.
• Atomic number is the number of protons.
• Atomic mass is the sum of protons and neutrons.
• Isotopes are atoms of the same element with different numbers of neutrons.
• Electron configuration describes the arrangement of electrons in energy levels and sublevels.
• Valence electrons are the electrons in the outermost shell, crucial for chemical bonding.

Periodic Table

• The periodic table organizes elements by increasing atomic number.
• Elements are arranged in periods (rows) and groups (columns).
• Elements in the same group have similar chemical properties due to similar valence electron configurations.
• Metals are generally good conductors of heat and electricity, located on the left side of the table.
• Nonmetals are generally poor conductors of heat and electricity, located on the right side of the table.
• Metalloids exhibit properties of both metals and nonmetals, located along the stair-step line.
• Groups have specific names (e.g., alkali metals, alkaline earth metals, halogens, noble gases).

Chemical Bonding

• Chemical bonding occurs when atoms combine to form molecules.
• Ionic bonding involves the transfer of electrons from a metal to a nonmetal, forming ions with opposite charges that attract.
• Covalent bonding involves the sharing of electrons between nonmetals.
• Metallic bonding involves the sharing of electrons among metal atoms.
• Polar covalent bonds occur when electrons are unequally shared between atoms, leading to a partial positive and partial negative charge (dipole moment).
• Electronegativity is the ability of an atom to attract electrons in a chemical bond.

Chemical Reactions

• Chemical reactions involve the rearrangement of atoms to form new substances.
• Reactants are the substances that undergo change.
• Products are the new substances formed.
• Chemical equations represent chemical reactions using symbols and formulas.
• Balancing chemical equations ensures the law of conservation of mass is obeyed (same number of each type of atom on both sides).
• Different types of reactions include synthesis, decomposition, single replacement, double replacement, combustion.

States of Matter

• Matter exists in three fundamental states: solid, liquid, and gas.
• Solids have a fixed shape and volume.
• Liquids have a fixed volume but take the shape of their container.
• Gases have no fixed shape or volume, expanding to fill their container.
• Phase changes involve transitions between these states (e.g., melting, freezing, vaporization, condensation, sublimation).

Solutions

• Solutions are homogeneous mixtures of two or more substances.
• The solute is the substance dissolved.
• The solvent is the substance doing the dissolving.
• Concentration expresses the amount of solute in a given amount of solvent or solution.
• Solubility describes the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.
• Factors affecting solubility include temperature and pressure.

Acids and Bases

• Acids are substances that release hydrogen ions (H+) in solution.
• Bases are substances that release hydroxide ions (OH-) in solution.
• The pH scale measures the acidity or basicity of a solution.
• A neutral solution has a pH of 7.
• Acids have a pH below 7, bases above 7.
• Strong acids and bases completely dissociate in solution; weak acids and bases only partially dissociate.
• Neutralization reactions occur when acids and bases react to form a salt and water.

Stoichiometry

• Stoichiometry deals with the quantitative relationships between reactants and products in a chemical reaction.
• Mole concept is central to stoichiometry, relating mass to moles and the number of particles.
• Molar mass connects mass and moles for a specific substance.

Thermodynamics

• Thermodynamics studies energy transfer and transformations in chemical and physical processes.
• First law of thermodynamics: energy cannot be created or destroyed, only transferred or transformed.
• Second law of thermodynamics: the entropy (disorder) of the universe tends to increase in spontaneous processes.
• Third law of thermodynamics: the entropy of a perfect crystal at absolute zero is zero.