Chapter 8: Chemical Concepts, Valency, and Reactions

Vocabulary flashcards covering chemical symbols, formulas, valencies, radicals, molecular formula rules, and types of chemical reactions.

Symbol

The short form of the name of an element (e.g., Hydrogen is $H$).

Formula

A short way of showing the elements present in a substance (e.g., Water is $H_2O$).

Valency

The combining capacity of an atom (e.g., Hydrogen valency is 1 and Oxygen valency is 2).

Monovalent Element

An element having a valency of 1, such as $H$, $F$, $Cl$, $Br$, $I$, $K$, $Na$, $Ag$, $Cu$, $Au$, $Li$, $Rb$, $Cs$, $Fr$, and $At$.

Divalent Element

An element having a valency of 2, such as $Be$, $Mg$, $Ca$, $Sn$, $Ba$, $Ra$, $O$, $S$, $Se$, $C$, $Zn$, $Fe$, $Co$, $Sn$, and $Pb$.

Trivalent Element

An element having a valency of 3, such as $N$, $P$, $Al$, $F$, and $Au$.

Tetravalent Element

An element having a valency of 4, such as $C$, $S$, $Sn$, and $Pb$.

Radical

A group of atoms that does not stay independent and participates in a compound like an elemental atom (e.g., Nitrate, $NO_3^-$).

Ammonium ($NH_4^+$)

A radical with a valency of 1.

Hydronyl ($OH^-$)

A radical with a valency of 1.

Nitrate ($NO_3^-$)

A radical with a valency of 1.

Bicarbonate ($HCO_3^-$)

A radical with a valency of 1.

Carbonate ($CO_3^{2-}$)

A radical with a valency of 2.

Sulphate ($SO_4^{2-}$)

A radical with a valency of 2.

Sulphite ($SO_3^{2-}$)

A radical with a valency of 2.

Phosphate ($PO_4^{3-}$)

A radical with a valency of 3.

Molecular Formula Rule 1 (Equal Valency)

If the valency of the elements or radical in a molecule of a compound is the same, it is not required to write the valency in the formula (e.g., $HCl$).

Molecular Formula Rule 2 (Multiple Valency)

If the valency of one element is a multiple of the valency of another element, the valencies of both elements are divided by that multiple (e.g., $C_2O_4 \rightarrow CO_2$).

Molecular Formula Rule 3 (Exchanged Valency)

If the valencies of both elements are different and not divisible by a common multiple, exchange their valencies and write them as suffixes (e.g., $Al_2O_3$).

Addition Reaction

A reaction where two or more substances combine to form a single new substance (e.g., $Fe + S \rightarrow FeS$, $2H_2 + O_2 \rightarrow 2H_2O$).

Combustion Reaction

A reaction where a substance burns in the presence of oxygen in the air and changes into another substance, during which heat is required or released (e.g., $S + O_2 \rightarrow SO_2$).

Displacement Reaction

A reaction where one element displaces another element from a compound and takes its place to form a new compound (e.g., $Fe + CuSO_4 \rightarrow FeSO_4 + Cu$).

Decomposition Reaction

A reaction where one compound breaks down into two or more simpler substances when heat is applied (e.g., $CaCO_3 \rightarrow CaO + CO_2$).

Neutralization Reaction

A reaction where an acid reacts with a base to produce a neutral substance (e.g., $CaO + 2CH_3COOH \rightarrow Ca(CH_3COO)_2 + H_2O$).

Endothermic Reaction

A chemical reaction in which the temperature of the mixture decreases because heat energy is absorbed from the surroundings (e.g., Baking soda + Citric acid $\rightarrow$ Sodium citrate + Carbon dioxide + Water).