NCERT Book Class 9 Science (Exploration) Chapter 9 Atomic Foundations of Matter

Chapter
Atomic Foundations
9 of Matter

Think It Over In Chapter 8, Journey Inside the Atom, you explored the structure
of the atom. You also studied subatomic particles, viz., electrons,
y Water can be protons and neutrons, in terms of their discoveries, properties and
obtained from locations in the atom. You also learnt that atoms with an octet of
various sources. Are electrons in their valence shell are stable. Atoms can lose, gain or
all these samples of share electrons to achieve an octet of valence electrons.
water chemically You have also learnt that many properties of the
identical? Grade 8
Curiosity elements are not retained when they form a compound.
y Oxygen is sometimes Chapter 8
For example, hydrogen and oxygen are gases, whereas the
represented as O
substance formed when they combine is water, which is a liquid at
and sometimes
ordinary temperatures.
as O2. What is the
difference between Interestingly, water does not have the same properties as hydrogen
these symbols? or oxygen. Hydrogen gas is combustible and oxygen supports
y Why does dissolved combustion, whereas water neither burns nor helps in burning;
salt in water conduct rather, it extinguishes fire. However, it was found that the mass of the
electricity, but sugar water formed equals to the sum of the masses of the hydrogen and
does not? oxygen that combined to form it. Let us explore whether the mass
remains unchanged during physical and chemical changes.