Chemistry Basics: Elements, Atoms, and Molecules

Symbol and Element

• Elements are represented by symbols.
• Single letter symbols are capitalized.
• Two letter symbols are capitalized with the first letter capitalized and the second letter lowercase.

Atomic Mass

• The mass of an atom is compared to the mass of a carbon-12 atom.
• One atomic mass unit (u) is 1/12th the mass of a carbon-12 atom.
• The atomic mass of an element is the average mass of one atom compared to 1/12th the mass of a carbon-12 atom.

Molecule

• A molecule is the smallest particle of an element or compound that exists independently and shows all the properties of that substance.
• A molecule can consist of two or more atoms.
• Atomicity is the the number of atoms present in one molecule.
• Molecules of elements can contain one or more atoms of the same element.
• Molecules of compounds contain two or more atoms of different elements.

Ions

• Ions are charged particles.
• Cations are positively charged ions.
• Anions are negatively charged ions.
• Valency is the combining capacity of an element.

Laws of Chemical Combination

• Law of Conservation of Mass: Mass cannot be created or destroyed in a chemical reaction. The total mass of reactants equals the total mass of products.
• Law of Constant Proportions: Elements in a compound are always present in a definite proportion by mass.

Dalton's Atomic Theory

• Matter is made up of tiny particles called atoms.
• Atoms are indivisible and cannot be created or destroyed in a chemical reaction.
• Atoms of a given element are similar in mass and properties.
• Atoms of different elements have different masses and properties.
• Atoms combine in small whole number ratios to form compounds.
• In a given compound, the relative number and kind of atoms are constant.

Atom

• An atom is the smallest particle of an element.
• The atomic radius is measured in nanometers (nm).

Writing Chemical Formulae

• Place the symbol of the metal or positive ion on the left.
• Place the symbol or formula of the non-metal or negative ion on the right.
• Write the valencies below the symbols.
• Cross over the valencies.
• Polyatomic ions should be enclosed in brackets before writing the formula.

Molecular Mass and Formula Unit Mass

• The molecular mass is the sum of the atomic masses of all the atoms in a molecule.
• Molecular mass is expressed in atomic mass units (u).

Mole Concept

• A mole of a substance contains 6.022 x 10^23 particles (atoms, molecules, or ions).
• This number is called Avogadro's Number or Avogadro's Constant.
• A mole represents a definite mass of a substance equal to the gram atomic mass of an element or the gram molecular mass of a compound.
• Gram atomic mass is the atomic mass expressed in grams.

This quiz covers fundamental concepts in chemistry, including atomic mass, molecular structure, and the characteristics of ions. Test your understanding of how elements are represented by symbols and the differences between cations and anions. Perfect for students looking to solidify their knowledge of introductory chemistry.