Chemical Formulae, Equations, and Relative Masses

Vocabulary flashcards covering chemical formulae, molecular and ionic representations, word and symbol equations, balancing rules, and relative atomic and formula masses.

Diatomic Molecule

A molecule composed of two atoms. Seven elements exist as diatomic molecules: hydrogen ($H_2$), nitrogen ($N_2$), oxygen ($O_2$), fluorine ($F_2$), chlorine ($Cl_2$), bromine ($Br_2$), and iodine ($I_2$).

Molecular Formula

A chemical formula that indicates the type of atoms present using chemical symbols and the exact number of each atom using subscript numbers.

Diagrammatic Representation of Molecules

A visual model using key-coded coloured spheres to depict the types, numbers, and structural arrangements of atoms within a simple element or compound.

Ionic Compound

A neutral substance formed when metals and non-metals react together, involving the metal losing electrons to form positive ions and the non-metal gaining electrons to form negative ions.

Polyatomic Ion

An ion composed of two or more atoms carrying an overall charge, such as carbonate ($CO_3^{2-}$), sulfate ($SO_4^{2-}$), hydroxide ($OH^-$), nitrate ($NO_3^-$), and ammonium ($NH_4^+$).

Swap-and-drop Method

A technique used to determine the chemical formula of an ionic compound with different ionic charges by swapping the magnitude of each charge to become the subscript for the opposite ion.

Word Equation

A chemical equation that shows the full chemical names of reactants on the left-hand side and products on the right-hand side separated by a reaction arrow.

Symbol Equation

A chemical equation using the formulae of reactants and products, balanced to show equal numbers of each atom on both sides of the equation.

State Symbols

Notations included in chemical equations to show physical states: solid $(s)$, liquid $(l)$, gas $(g)$, and aqueous solution $(aq)$.

Catalyst

A substance added to a chemical reaction to increase its speed, often written above the arrow in a chemical equation.

Law of Conservation of Mass

The scientific law stating that mass cannot be created or destroyed in a chemical reaction, requiring the total mass of reactants to equal the total mass of products.

Dissociation

The process in aqueous solutions where soluble ionic compounds separate into their component positive and negative ions.

Ionic Equation

A chemical equation written for reactions in aqueous solution where soluble ionic substances are shown as separate ions, and spectator ions appearing on both sides are omitted.

Relative Atomic Mass ($A_r$)

The average mass of an atom of an element compared to carbon-12, which serves as the standard atom with a fixed mass of $12$ units.

Relative Molecular Mass ($M_r$)

The sum of the relative atomic masses ($A_r$) of all the atoms present in a molecular chemical formula.

Relative Formula Mass ($M_r$)

The sum of the relative atomic masses ($A_r$) of all the atoms present in the formula unit of an ionic compound.