Atoms and molecules with question and answers.

1. Atoms
And
Molecules

2. Introduction

3. Atom

4. • The basic structural unit of an element is atom.
• Atom is the smallest part of a chemical element.
• All matters in the universe is made up of very tiny
particles called atom.
• Atom comprise of nucleus and electrons.
• There are 92 different kinds of atoms in nature.
• Two or more identical or different atoms bond
chemically.
• The combination of this 92 different kinds of atoms
form different kinds of matter that we see all
around.

5. Molecules

6. • A molecule consists of two or more atoms.
• Molecules is a set of atoms held together by a
bond representing the smallest unit of a
compound.
• Molecules of compounds is the smallest unit of a
chemical compound and has the same chemical
properties of that compound.
• Molecules of a compound have atoms of two or
more different elements.
• Molecules can vary greatly in size and complexity.

7. Element

8. • The element is the substance that consists r made
entirely of only one type of atom.
• Such elements are said to be monatomic.
• Since there are 92 different kinds of atoms in
nature, there are 92 different kinds of elements.
• Helium (He) is a monatomic element.
• Some examples of monatomic elements are gold,
silver, iron, potassium.
• Element hydrogen contains a single proton and a
single electron.
• Element having same number of protons when
arranged differently a different form of element is
formed i.e.
• When the number of protons change the type of
element changes.

9. • For example two hydrogen (H2) atoms come
together to form hydrogen molecule.
• Two oxygen (O2) atoms come together to form
oxygen molecule.
• Similarly two chlorine (Cl2) atoms com together to
form a chlorine molecule.
• All elemental molecules are made of atoms of a
single element but atoms of some elements like
Neon, Argon do not bond with other atoms to form
a molecule.

10. Compounds

11. • A compound is a molecule made up of atoms from
different elements.
• All compounds are molecules but not all molecules are
compounds.
• For example hydrogen gas (H2) is a molecule, but it is
not a compound as it is made up of one-one element
i.e. hydrogen.
• Water (H2O) has three atoms, two hydrogen (H) atoms
and one oxygen (O) atom.
• Cam be called as a molecule or a compound because it
is made up of two different atoms as hydrogen and
oxygen.
• Carbon dioxide molecule consists of one carbon atom
bonded to two oxygen atoms whereas sulphuric acid
molecule consists of one sulphur atom, two hydrogen
atoms and four oxygen atoms.

12. • Such substances, which are made by the
combination of two or more kinds of elements are
called compounds.
• The atoms in a compound are chemically bonded
and hence cannot be separated easily.
• When compounds are formed they lose many of
their individual properties.
• They have a new life on their own.

13. Molecular
Formula

14. • Though the total number of atoms are limited in nature,
there are millions of different substances around us.
• This is because they are all made up of different types of
molecules.
• Molecules are made up of different types of atoms and the
ratios of the atoms in molecules also are different.
• For example oxygen that we breathe has two molecules of
oxygen however the ozone layer which is made up of
oxygen as well has molecules that are formed by the
bonding of three atoms of oxygen.
• Hence the oxygen the we breathe is represented as O2 and
the ozone molecule is represented as O2 and the ozone
molecule is represented as O3.
• Here the number 2 and 3 represent the number of atoms
of the element oxygen that have bonded to form the
molecule.

15. • Water is represented as H2O where H stands for
Hydrogen, 2 for the two atoms of hydrogen and O
for the single atom of oxygen that has bonded to
form a molecule of water.
• Molecule of hydrogen peroxide contains two atoms
of hydrogen and two atoms of oxygen so its
molecular formula is H2O2
• Particles can be atoms molecules or ions
• Atoms are single neutral particles
• Molecules are neutral particles made of two or
more atoms bonded together.

17. Some Simple
Molecular
Formulae

19. Common name Molecular formula
Water H2O
Carbon dioxide CO2
Ammonia NH3
Carbon dioxide CO2
Glucose (sugar) C6H12O6
Hydrochloric acid HCl
Sulphuric acid H2SO4
Acetic acid (vinegar) CH3COOH
Methane CH4
Sodium chloride NaCl

27. Multiple
Choice
Questions

28. 1) At least _______ atoms are required to form a
molecule.
a) 1
b) 2
c) 3
d) 4
2) Compound is a molecule made up of atoms from
_________ elements.
a) Similar
b) Same
c) Different
d) All of these
b) 2
c) Different

29. 3) Ozone has __________ atoms of oxygen.
a) 1
b) 2
c) 3
d) 4
4) O3 is a/an ________
a) Compound
b) Element
c) atom
d) Molecule
5) Molecular formula of carbon-dioxide is ________
a) CO
b) C2O2
c) C2O
d) CO2
c) 3
d) Molecule
d) CO2

30. 6) In the formula for table sugar which is C12H22O11
there are ________ atoms of hydrogen.
a) 12 b) 22
c) 11 d) 45
7) Oxygen that we breath has _____ atoms of oxygen.
a) 1 b) 2
c) 3 d) 4
8) Molecules of any substances have
_______structure.
a) Same b) different
c) Cannot say d) none
b) 22
b) different
b) 2

31. 9) Water molecule contains _____ atoms of
hydrogens and _____ atom/s of oxygen.
a) One , two b) two, one
c) two , two d) one, one
10) Molecular formula of hydrogen peroxide is _____
a) HO b) H2O
c) H2O2 d) HO2
11) Methane has _____ hydrogen atoms.
a) 2 b) 3
c) 4 d) 5
b) two, one
c) H2O2
c) 4

32. 12) Molecular formula of ammonia is NH3. here number 3
represents the number of ______ of elements hydrogen.
a) Atoms
b) Electrons
c) Bonds
d) None of these
13) Hydrogen gas (H2) is a/an _____ but it is not a/an ___
a) Atom, molecules b) molecule, atom
c) Compound, molecule d) molecule, compound
14) Atoms of some elements like _____ do not bond with other
atoms to form a molecule
a) Helium
b) Hydrogen
c) Sodium
d) Potassium
a) Atoms
d) molecule, compound
a) Helium

33. 15) Molecular formula of vinegar is ________
a) C6H12O6 b) CH4
c) CH3COOH d) CH2COOH
16) Molecules vary greatly in size and complexity.
a) True b) false
17) Ratios of the atoms in different molecules is
always same.
a) True b) false
c) CH3COOH
a) True
b) false

34. 18) Total number of atoms are limited.
a) True b) false
19) Sulphuric acid molecule consists of one sulphur
atom, two hydrogen atoms and two oxygen atoms.
a) True b) false
20) Molecular formula of hydrochloric acid is
HCl.
a) True b) false
a) True
b) false
a) True