UNIT NO.5
Elements and Compounds
(Solved Exercise)
6.1 Encircle the correct option.
6.2 Write short answer.
1. Define element.
An element is a substance which consists of only one kind of atoms.it is the simplest form of matter. It cannot be broken down into further simpler substances by the ordinary chemical reactions.
2. Write the names and symbols of any two metals.
i. Iron Fe
ii. Gold Au
iii. Lithium Li
iv. Beryllium Be
3. Write the names and symbols of any four non-metals.
i. Carbon C
ii. Nitrogen N
iii. Oxygen O
iv. Fluorine F
4. Write the names and symbols of any three noble gases.
i. Helium H
ii. Neon Ne
iii. Argon Ar
5: Write the names and formulae of any five compounds.
i. Ammonia NH3
ii. Methane CH4
iii. Sodium chloride NaCl
iv. Suger C12H12011
v. Water H2O
6.3 Differentiate the followings:
i. Atom and molecule
Atom
An atom ist allest particle of an elementhat can take part in a chemical reaction.
Molecule
The atoms of noble gases and the groups of two or more atoms which can exist independently are called molecules.
2. Element and compound
Element
An element is a substance which consists of only one kind of atoms.it is the simplest form of matter. It cannot be broken down into further simpler substances by the ordinary chemical reactions. For example Iron Fe, Water H2O
Compound
A compound is a pure substance that contains two or more kind of elements combined chemically in a fixed ratio. For example Ammonia NH3, Water H2O
3: Metal and non-metal
Metals
Metals are tipically shiny solids that have to moderate hight melting points. They are good conductors of both heat and electricity. Important examples of common metals are lithium, iron, copper, gold etc.
Non-metals
Non-metals are dull substances having relatively low melting points. They are often poor conductors of heat and elecricity. Common examples of non-metals are carbon, nitrogen, oxygen fluoring ete.
4. Metalloid and noble gas
Metalloid
The group of elements whose properties resemble with both the metals and non-metals are called metalliods. Boron (B), silicone (Si) are the examples of metalloids.
Noble gas
The group of elements which have stable electronic configrations of their atoms and can exist independently are called nobles gase. Helium H , neon Ne and argon Ar are the examples of noble gases.
5. Monoatomic molecule and polyatomic molecule
Monoatomic molecule
A molecule consisting of one atom only is called mono atomic molecule.
Polyatomic molecule
A molecule consisting of three or more than three atoms is called mono polyatomic molecule.
6.4 Constructed Response Questions.
1.N2, O2, CO2, and H2O are chemical formulae representing the molecules of different of different substances.
a) Which of these are the elements and which are the compounds?
N2 and O2 are the elements while CO2, and H2O are the compounds.
b) How many atoms are present in each chemical formula?
N2 : 2 atoms
O2 : 2 atoms
CO2 : 3 atoms
H2O : 3 atoms
c) Identify the elements present in each chemical formula.
N2 : Nitrogen
O2 : Oxygen
CO2 : Carbon and Oxygen
H2O : Hydrogen and Oxygen
2. Elements listed in Group-18 of the Periodic Table are known as noble gases.
(a) Why are these called noble gases?
Because they never take part in chemical reactions.
(b) How are noble gases different from other elements?
The electronic configration of the atoms of noble gases are stable as compared to other elements.
(c) Is there any use of noble gases in daily life?
Yes, noble gases have many uses in daily life. For example Helium is filled in weather balloons. Neon is used in neon-sign boards.