Sructure of matter edited 0611

Grade 7
Structure of Matter
Prepared By; Ms Mehak Mayariwala
Qualification : M.Sc B.ed (Organic Chemistry)
School :Ryan International School CBSE

 FIND THE ODD ONE OUT
o Matter, solid, liquid, gas
o wood, stone, milk, ice

CORRECT
ANSWER :
MATTER
REASON- REST THREE ARE STATES OF
MATTER
MILK
REASON-REST ARE IN SOLID STATE
IF YOU CRACK ALL THE CORRECT ANSWERS THEN YOU
ARE A RYANITES

Any thing which occupies
space and has some mass
is called a Matter

 Ancient Greek philosophers thought that matter was made up of Fire ,air , earth and
water.
 MAHARSHI KANADA was ancient Indian scientist, sage and philosopher who
originated the idea that ANU (ATOM)
 DEMOCRITUS was a Greek philosopher who was the first person to use the term
ATOM (ATOMOS: MEANING INDIVISIBLE). He thought that if you take a piece
of matter and divide it and continue to divide it you will eventually come to a point
where you could not divide it any more.

 John Dalton was the first to adapt Democritus’ theory into the
first modern atomic model
JOHN DALTON’S ATOMIC MODEL
 All matter consists of tiny particles called atoms
 Atoms are indestructible and unchangeable
 When elements react, it is their atoms that have combined to form new
chemical compound.

I. A piece of chalk is made up of Matter. If this
piece of chalk is broken ,what happen ?

 If we continue breaking this piece of chalk ,it forms stills
smaller and smaller chalks.
 However ,this must end somewhere.
 It should be possible to get the smallest piece of chalk
that cannot be broken any further.
 John Dalton, a scientist of the nineteenth century
,named this smallest piece of chalk as the Chalk Atom.
 Similarly, the smallest piece of gold is Gold atom.

 Atoms are so small that they cannot be seen even by
the most powerful microscope.
Atoms
 The smallest particles of gold and chalk are gold atoms
and chalk atoms respectively.
 Atoms are made up of Sub – atomic Parts
Eg : electrons,protons and neutrons.

FIND ODD ONE OUT:
(1) Electron , proton , neutron , nucleus , compound
...

Correct Answer -
Compound
Reason – All other are within the
atom but Compound is
combination of two or more
atoms.

Question 2
Name the three things that makes up an atom

CORRECT
ANSWER
ELECTONS
NEUTRONS
PROTONS

? However, the smallest particles of water is
not a water atom.

 This is because water is made up of two
different kinds of atoms -
O H2
 The smallest particle of
water contains two atoms
of HYDROGEN and one
atom of OXYGEN
H2O
These form One Molecule of water

 Fe, Au,H2 ,O – Substances made
up of only one Kinds of atoms.
They are called elements.
 The smallest particle of a element
is atom
Elements

 NaCl , NH3 , C6H12O6- are pure
substances that are made of two or
more elements that are chemically
bonded or combined .They are called
compounds.
 The smallest particle of a compound is
molecule
COMPOUNDS

 Properties of compounds:
 A compound always contains the same elements combines together
chemically in fixed ratio eg : No matter from where you take water ,it
will always contain hydrogen and oxygen in the ratio of 2:1 by volume.
 The properties of a compound are different from those of its constituent
elements. Eg: the properties of water (a liquid) are different from its
constituent elements, i.e hydrogen (a gas) and oxygen (a gas) .water
puts off fire, whereas hydrogen burns and oxygen supports burning.

Question 2
Air is a Mixture or compound ?

CORRECT
ANSWERS:
AIR IS THE MIXTURE
BECAUSE IT HAS MANY
GASES SUCH ;O2 ,CO2,
N, H ,He

LET’S ANSWER
 WHAT IS THE DIFFERENCE BETWEEN THE SMALLEST
PARTICLE OF AN ELEMENT AND THE SMALLEST
PARTICLE OF A COMPOUND?

ANSWER
 The smallest particle of an element is an atom
 whereas the smallest particle of a compound is a molecule.
 The difference between an atom and a molecule is that the atom is the
smallest unit of an element.

ANSWER
 molecule is formed when two or more similar
types of atoms are joined chemically. e.g. 'O', 'H',
and 'C', etc are atoms but O2, H2, and N2, etc are
molecules.

 MIXTURES
o When two or more elements or
compounds are mixed together,
and there is no chemical change
between them, we get a mixture of
the elements or compounds.
o In a mixture no new molecules are
formed.

 Firstly ,not all elements or compounds can react with each
other.
 Secondly, even if they can react with each other, they will not
do so until conditions are favourable.
 For example, some compounds may have to be heated
together to make them react. Others may have to be
dissolved in water before they can react.
Mixtures

Activity 1 (Experiment
investigation)
Put some powdered iron and some powdered sulphur in a china
dish. Mix them thoroughly. Now bring a magnet near them.
You will find that the powdered iron in the mixture is attracted by
the magnet. The magnet can be used to completely separate iron
and sulphur
Statement It is clear From the above activity that iron and sulphur have not reacted
chemically.

QUESTION-2
 When two elements are brought together, they
OPTIONS :
(a) always form a mixture
(b) always form a compound
(c) may form a mixture of a compound depending on the conditions
(d) may form a mixture or a compound depending on what they like.

CORRECT ANSWER
C) may form a mixture or a compound
depending on the conditions
REASON - Not all elements react with each
other, and in case they react, they will need a
condition favoring such reaction

Symbols
 We know that there are only 118 elements and millions of compounds.The
elements and compounds react with each other in innumerable ways.
 Writing the full names of elements and compounds., and describing their
reactions is very inconvenient .
 It is more convenient to use abbreviations or symbols

Symbols
 We use symbols to represent elements.
 A compound is represented by a formula which contains symbols of
all the elements present in a molecule of that compound
Symbols of elements: C ,O ,N , H, fe , S , Cu , He , Cl ,Ca ,Au etc.
Examples : HCl ,FeS , NaCl ,MgO Mgcl2
chlorineHydrogen magnesium chloride

Early scientists
 Alchemists used picture symbols to represent elements
 Later,Dalton improved over these symbols.
But as the number of
known elements and
compound increased
,this method too
became very tedious.
Opps !

Symbols
 The present system uses letters of the English alphabet to
represent elements.it was first suggested by Berzelius,
The system is as follows:
 Some elements are represented by using the first letter (in
capitals) of the name of the element. for example , C for
carbon , N for nitrogen ,O for oxygen.
 Names of some elements have the same initial letter, for
examples, carbon ,calcium and cobalt. In such cases, the
first letter is taken in capitals together with letter(in small)
from its name ,for examples ,Ca for calcium , Co for cobalt ,
Ba for barium , Br for bromine

 The symbols of some elements are derived from their latin
names, for examples,
 The latin name of copper is cuprum and its symbol is Cu.
 The latin name of potassium is Kalium and its symbol is K.
Element Latin
Name
Symbol
aluminium Al
calcium Ca
carbon C
chlorine Cl
copper cuprum Cu
Element Latin
Name
Symbol
gold aurum Au
iron ferrum Fe
potassium kalium K
sodium natrium Na
tungsten wolfrum Whydrogen H Oxygen O

 Chemical Formula?
A formula in chemistry is a type of shorthand for representing the
elements in a compound.
 Symbols from the periodic table are used for the individual elements.
 e.g. O for oxygen, H for hydrogen, C for carbon, N for nitrogen, Ca for
calcium and Na for sodium.
 In formulas and equations, the chemical formula for water is H2O which
indicates that 2 atoms of Hydrogen combines with 1 atom of oxygen.
 The chemical formula for sodium chloride is NaCl indicating that
one atom of sodium combines with one atom of chlorine in a one-to-one
ratio.
 The equation for magnesium bromide MgBr2 which indicates that one
magnesium atom combines with two bromine atoms
FORMULAE

 In some compounds, two or more elements act together as a
single group.
 Examples of some compounds having such group are given in
Table
COMPOUND FORMULA
Hydrochloric acid HCl
Iron Sulphate FeS
Magnesium Chloride MgCl2
Magnesium Oxide MgO
Sodium Oxide Na2O
Carbon Dioxide CO2
Sodium chloride NaCl

 Atom of some element cannot exit independently in nature they form
molecule containing two or more atom.
 H2 represent the molecule of hydrogen
 O₂ Oxygen
 Cl2 Chlorine
 N2 Nitrogen

Atomicity is defined as the total number of atoms that constitute a molecule.
For example, each molecule of oxygen (O2) is composed of two oxygen
atoms. So atomicity of oxygen is 2. On the basis of atomicity, molecules
can be classified as :
Monoatomic-composed of 1 atom e.g. He, Ne, Ar (all noble gases are
monoatomic)
Diatomic-composed of 2 atoms e.g. H2 , N2 , O2, ,Br2 , I2 , Cl2
Triatomic-composed of 3 atoms e.g. O3 ,H2O, Co2 , No2, So2 , ,H2S , CaCl2, MgO2
Polyatomic-composed of 3 or more atoms e.g. P4 , S8,
ATOMICITY

Valency can be defined as the combining capacity of any atom . .... In
an atom, the valence electrons are the electrons that can be used in
combining with other atoms - these are the electrons in the orbitals of
the outermost shell also referred as Valence Shell.

PERIODS •Each row is called a “period”

GROUPS
Group 1
Group 2
Group 8 = 8 electrons
•Each column is
called a “group”

DETERMINE THE NUMBER OF SHELLS
AND THE NUMBER OF VALENCE
ELECTRONS FOR:
2nd Period = 2 shells
4 valence
electrons
6

DETERMINE THE NUMBER OF SHELLS
AND THE NUMBER OF VALENCE
ELECTRONS FOR:
3rd Period = 3 shells
1 valence
electron
11

Hydrogen
1 shell
1 valence electron
Name the element.
Number of shells ?
Valence electrons ?
1

Name the element.
Number of shells ?
Valence electrons ?
Neon
2 shells
8 valence electrons
10

Beryllium
2nd Period = 2 shells
2nd Group = 2 valence
electrons
Name the element.
Number of shells ?
Valence electrons ?
4

Sulfur
3 shells
6 valence electrons
Name the element.
Number of shells ?
Valence electrons ?
16

Potassium
4 shells
1 valence electron
Name the element.
Number of shells ?
Valence electrons ?
19

Name the element.
Number of shells ?
Valence electrons ?
Helium
1 shell
2 valence electrons
•Helium is the exception.
•Since it has just one shell, that shell
can only fit 2 electrons instead of 8.
2

Group 1 = 1 electron

VALENCIES OF SOME COMMON ELEMENTS AND
GROUP

 Writing a formula
We can write the formula of a compound if we know:
 The symbols of the elements /groups it is made up of ,and
 The valencies of the elements/groups it is made up of.

The steps involved are as follows:
Write the symbols of the elements/groups side by
side .write their valencies on top as superscripts of
their symbols.
Divide by any common factor in their valencies.
Interchange the numbers obtained and write them
at the base (as subscripts) to get the formula.

 Writing of chemical formulae of some compounds
compound Elements /groups
with valencies
formula
Hydrochloric acid H1Cl1 HCl
Sulphuric acid H1(SO4)2 H2SO4
Nitric acid H1(NO3)1 HNO3
Sodium carbonate Na1(Co3)2 Na2Co3
Sodium nitrate Na1(No3)1 NaNO3
Calcium chloride Ca2Cl1 CaCl2.

 Chemical Equations:
A chemical equations (or simply
equations) shows the result of a
chemical reaction in which the
reactants and the products are
represented by symbols or
formulae.

 Writing the formula for ammonia
 The element in ammonia are nitrogen and hydrogen.
 The valency of nitrogen is 3 and that of hydrogen is 1. so ,we write
them as superscripts N3H1
 There is no common factors in the valencies 3 and 1 . So ,we move
on to the third step.
 Interchanging the valencies and writing them as subscripts we get
the formula of ammonia as
NH3

The elements or compounds that take part in a chemical
change (or chemical reaction) are called the reactants.
The rearrangement of the elements form new
compounds in the reaction.These are called products.
H + Cl HCl
Reactants Products

In a chemical equations,
Between the reactants and the products is placed
the sign = or
 The reactants are written on the left – hand side of the arrow.
 The products are written on the right hand side of the arrow.
C + O2 CO2
reactants Products

 An important requirement for writing an equation is that the number of
atoms of each element on the left-hand side should be the same as the
number of atoms on the right – hand side.
Can we write water :?
 Water can be broken up into its constituent elements,
hydrogen and oxygen.
H2O H + O

The answers is NO
Reason  Because hydrogen and oxygen cannot exist as independent
atoms.
 They must be represented as H2 and O2 respectively.
 Also the number of hydrogen atoms on the left hand side should
be equal to number of hydrogen atoms on the right hand side of
the equations.
Can we write : H2O H2 + O2 ?

Once again the answer is NO
Reason – because the number of atoms of oxygen on the
left and right hand side should be the same.
Can we write : 2H2O 2H2 + O2 ?
YES, we can . We now have 4 atoms of hydrogen and 2
atoms of oxygen on both sides of the equation. Such an
equation is called a balanced chemical equation.

Some examples are as follows:
Nitrogen reacts with hydrogen to give ammonia.
N2 + H2 NH3 ( unbalanced)
N2 + 3H2 2NH3 (Balanced)
Subscripts represent
the number of atoms
of the element
 Nitrogen : 2 atoms
 A formula may begin with a number.
 If there is not a number ,then “1”is
understood to be in front of the formula.
 This number is called the coefficient

 Sodium reacts with water to give sodium hydroxide and hydrogen
Na + H2O NaOH + H2
FIRST
STEP
To check the equation is balance or unblanced
LHS RHS
Na =1
H = 2
O =1
Na =1
H = 3
O =1
TOTAL =04 TOTAL =05
 Thus equation is Unbalanced
 Because no of atoms in LHS AND RHS are not same.

 Sodium reacts with water to give sodium hydroxide and
hydrogen
Na + H2O NaOH + H2 (unbalanced)
2Na + 2 H2O 2NaOH + H2 (balanced)
To balancing the equation (2) coefficient is added to Na, (2) coefficient
is added to H2O , (2) coefficient is added to NaOH ,so to get number
of elements to be balanced.

 Zinc reacts with hydrochloric acid to give zinc chloride and
hydrogen.
Zn + HCl ZnCl2 + H2
LHS LHS
Zn = 01
H = 01
Cl = 01
Zn = 01
H = 02
Cl = 02
Total = 03 Total = 05
Thus equation is Unbalanced
Zn + 2HCl ZnCl2 + H2
LHS RHS
Zn = 01
H = 02
Cl = 02
Zn = 01
H = 02
Cl = 02
Total = 05 Total = 05
Thus equation is balanced
To balancing the equation (2) coefficient is added to HCL ,so to
get number of elements to be balanced.

Sructure of matter edited 0611

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