A) DIFFERNTIATE BETWEEN. a) Valency and variable valency
b) Atomic number, atomic mass
c) Metalloid and nobel gas
d) Periodic and non periodic change
e) Liquifaction and solidification
Answers
a) Valency is the combining capacity of an element. You can say that for a metal, it's valency is the number of valence electrons it has and for a non metal, it's 8 minus the number of valence electrons. The changed valency or valencies are called the variable valency.
b) The major difference between atomic number and mass number is that the atomic number states the number of protons present in an atom whereas, the mass number indicates the total of the number of protons and the number neutrons present in an atom.
c) Metalloids are those substances which have some properties of metals and some of non-metals e.g. boron, silicon. Noble gases are those which do not react chemically with other elements or compounds e.g. helium, neon, etc.
d) Events that repeat themselves after a fixed period of time and whose occurrence can be predicted are called periodic changes. The events that do not repeat themselves after regular interval of time are called non periodic changes.
e) Liquefaction is the conversion of gas to liquid where as solidification is the conversion of liquid to solid.