Atoms, Molecules, and Elements

• Atoms form the fundamental components of matter.
• Atoms consist of positively charged protons, neutral neutrons, and negatively charged electrons.
• The number of protons defines the element.
• The number of neutrons defines the isotope.
• The number of electrons defines the ion.

Molecules

• Molecules arise when chemical bonds hold two or more atoms together.
• Chemical bonds are either covalent or ionic
• Covalent bonds involve atoms sharing electrons.
• Ionic bonds involve atoms transferring electrons, creating ions.
• Molecules range from simple, like hydrogen gas (H2), to complex, like proteins.
• A molecule's properties depend on its constituent atoms and their arrangement.

Elements

• Elements constitute pure substances containing only one type of atom.
• Elements cannot be broken down into simpler substances through chemical means.
• The periodic table organizes elements by atomic number and chemical properties.
• Examples of elements include hydrogen (H), oxygen (O), and carbon (C).

Compounds

• Compounds are substances formed from two or more elements chemically bonded.
• Compounds have a chemical formula showing the fixed ratio of each element's atoms.
• Compounds break down into simpler substances through chemical reactions.
• Water (H2O), carbon dioxide (CO2), and sodium chloride (NaCl) serve as compound examples.
• A compound's properties differ from those of its constituent elements.

Chemical Reactions

• Chemical reactions rearrange atoms and molecules, leading to new substances.
• Chemical equations represent chemical reactions.
• Reactants (starting materials) and products (formed substances) appear in chemical equations.
• Balanced chemical equations have equal numbers of each element's atoms on both sides.
• Chemical reactions involve breaking and forming chemical bonds.
• Energy is either released or absorbed during a chemical reaction.
• Exothermic reactions release energy.
• Endothermic reactions absorb energy.

Types of Chemical Reactions

• Synthesis reactions combine two or more reactants into a single product represented as A + B → AB.
• Decomposition reactions break down a single reactant into two or more products represented as AB → A + B.
• Single displacement reactions involve one element replacing another in a compound represented as A + BC → AC + B.
• Double displacement reactions involve two compounds that exchange ions or elements represented as AB + CD → AD + CB.
• Combustion reactions describe a substance reacting rapidly with oxygen, producing heat and light.

Balancing Chemical Equations

• Balancing chemical equations fulfills the requirements of the law of conservation of mass.
• The law of conservation of mass dictates that matter remains uncreated and undestroyed in a chemical reaction.
• Coefficients are placed before chemical formulas to balance equations and equalize the number of atoms for each element on both sides.
• Initial balancing should focus on elements appearing in only one reactant and one product.
• Polyatomic ions should be balanced as a single unit if unchanged on both sides.
• Fractional coefficients can be used if necessary, but the entire equation should be multiplied to clear fractions.
• Validation ensures the number of atoms for each element matches on both sides of the equation.

States of Matter

• Solid: Matter possessing fixed shape and volume.
• Liquid: Matter possessing fixed volume but no fixed shape.
• Gas: Matter lacking fixed shape or volume.
• Aqueous: A substance dissolved in water.
• Chemical equations use abbreviations to show the state of matter: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous.