Chemical Bonding Flashcards
attractive force which holds the atoms together is called a .
bond
A chemical bond may be defined as the force of attraction between the atoms that binds them together as a unit called
molecule
Atoms of various elements combine together in different ways to form
chemical compounds
Who gave successful explanation based upon the concept of electronic configuration of noble gases about why atoms combine to form molecules
Kossel and Lewis
the noble gas atoms neither have any tendency to gain nor to lose electrons and hence their valency is
zero
They are inert that they even do not form diatomic molecules and exist as .
monoatomic gaseous atoms
The number of electrons lost from a metal atom is the ______ and the number of electrons gained by a not metal is the ______
valency of the metal
valency of the non-metal
Kossel and Lewis proposed theory in ______ to explain chemical combination between atoms
1916
Kossel and Lewis proposed theory in 1916 to explain chemical combination between atoms and this theory is known as ‘
Electronic theory of valence’ or Octet rule.
According to this, atoms of all elements, other than inert gases, combine to form molecules
because they have configuration. incomplete valence shell and tend to attain a stable electronic configuration similar to noble gases. Atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to achieve the stable outer shell of eight electrons.
The tendency of atoms to have eight electrons in the valence shell is known as the
Octet rule’ or the ‘Rule of eight
When atoms combine to form compounds, their valence electrons involve in bonding. Therefore, it is helpful to have a______ method to depict the valence electrons in the atoms
Lewis dot structure
The Lewis dot structure or electron dot symbol for an atom consists of the symbol of the element surrounded by dots representing the electrons of the valence shell of the atom.
The unpaired electron in the valence shell is represented by a _____ whereas the paired electrons are represented by a ____
single dot
pair of dots.
An ionic bond is a chemical bond formed by the _____ between positive and negative ions.
electrostatic attraction
The atom that loses electrons will form a _____ and the atom that gains electrons will form an ____
cation (positive ion)
anion (negative ion).
the bond is between the ions, it is called _______
Ionic bond
the attractive forces being electrostatic, the bond is also called
Electrostatic bond.
(ionic bond) the valence concept has been explained in terms of electrons, it is also called as
Electrovalent bond.
In general, _____ bond is formed between a metal and non-metal
ionic
The number of electrons that an atom of an element loses or gains to form an electrovalent bond is called its .
Electrovalency
The atomic number of Sodium is 11 and its electronic configuration is 2, 8, 1. It has one electron excess to the nearest stable electronic configuration of a noble gas Neon.
So sodium has a tendency to lose one electron from its outermost shell and acquire a stable electronic configuration forming sodium cation (Na+).
The atomic number of chlorine is 17 and its electronic configuration is 2, 8, 7. It has one electron less to the nearest stable electronic configuration of a noble gas - Argon.
So chlorine has a tendency to gain one electron to acquire a stable electronic configuration forming chloride anion (Cl-).
Characteristics of lonic compounds
Physical States
These compounds are formed because of the strong electrostatic force between cations and anions which are arranged in a well-defined geometrical pattern. Thus ionic compounds are crystalline solids at room temperature.
Characteristics of lonic compounds
Electrical conductivity
Ionic compounds are crystalline solids and so their ions are tightly held together. The ions, therefore, cannot move freely, and they do not conduct electricity in solid state. However, in molten state their aqueous solutions conduct electricity.
Characteristics of lonic compounds
Melting point:
The strong electrostatic force between the cations and anions hold the ions tightly together, so very high energy is required to separate them. Hence ionic compounds have high melting and boiling points.
Characteristics of lonic compounds
Solubility
: Ionic compounds are soluble in polar solvents like water.
They are insoluble in non-polar solvents like benzene (C₂H₂), carbon tetra chloride (CCI).
Characteristics of lonic compounds
Density, hardness and brittleness:
Ionic compounds have high density and they are quite hard because of the strong electrostatic force between the ions. But they are highly brittle./
Characteristics of lonic compounds
Reactions
: Ionic compounds undergo ionic reactions which are practically rapid and instantaneous.
the covalent bond is formed because of the sharing of electrons which become common to both the atoms, it is also called as
atomic bond
Atoms can combine with each other by sharing the unpaired electrons in their outermost shell.
Covalent bond
Covalent bonds are of three types:
- Single covalent bond represented by a line (-) between the two atoms. Eg. H-H
- Double covalent bond represented by a double line (=) between the two atoms. Eg. O=O
- Triple covalent bond represented by a triple line (=) between the two atoms. Eg. N=N
Characteristics of Covalent compounds
Physical state
: Depending on force of attraction between covalent molecule the bond may be weaker or stronger. Thus covalent compounds exists in gaseous, liquid and solid form. Eg. Oxygen-gas; Water-liquid: Diamond-solid.
____ compounds exists in gaseous, liquid and solid form.
covalent
Characteristics of Covalent compounds
Electrical conductivity:
Covalent compounds do not contain charged particles (ions), so they are bad conductors of electricity.
Characteristics of Covalent compounds
Melting point:
Except few covalent compounds (Diamond, Silicon carbide), they have relatively low melting points compared to ionic compounds.
Characteristics of Covalent compounds
Solubility
: Covalent compounds are readily soluble in non-polar solvents like benzene (CH), carbon tetra chloride (CCI).
They are insoluble in polar solvents like water.
Characteristics of Covalent compounds
Hardness and brittleness
: Covalent compounds are neither hard nor brittle.But they are soft and waxy.
Characteristics of Covalent compounds
Reactions
: Covalent compounds undergo molecular reactions in solutions and these reactions are slow.
Polar solvents contain bonds between atoms with very different electronegativities, such as oxygen and hydrogen. Ionic compounds are soluble in polar solvents. Ex:
water, ethanol, acetic acid, ammonia
Non polar solvents contain bonds between atoms with similar electro negativities, such as carbon and hydrogen. Covalent compounds are soluble in non- polar solvents. Ex:
acetone, benzene, toluene, turpentine
in ______, Kazimierz Fajans found, through his X-Ray crystallographic studies, that some of the ionic compounds show covalent character
1923
Fajan rule
that some of the ionic compounds show covalent character
When the size of the cation is small and that of anion is large, the bond is of more covalent character
Greater the charge of the cation, greater will be the covalent character
the formation of a covalent bond between two atoms takes place by the sharing of two electrons, both of which comes from only one of the combining atoms. This bond is called
Coordinate covalent bond or Dative bond.
Mostly the lone pair of electrons from an atom in a molecule may be involved in the dative bonding The atom which provides the electron pair is called ______ while the other atom which accepts the electron pair is called _______
donor atom
acceptor atom)
Characteristics of coordinate covalent compounds
Physical state
: These compounds exist as gases, liquids or solids
Characteristics of coordinate covalent compounds
Electrical conductivity
: Like covalent compounds, coordinate compounds also do not contain charged particles/ (ions), so they are bad conductors of electricity.
Characteristics of coordinate covalent compounds
Melting point:
These compounds have melting and boiling points higher than those of purely covalent compounds but lower than those of purely ionic compounds.
Characteristics of coordinate covalent compounds
Solubility
: Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, CCl, and toluene.
Characteristics of coordinate covalent compounds
Reactions
: Coordinate covalent compounds undergo molecular reactions which are slow.
When an apple is cut and left for sometimes, its surface turns brown. Similarly, iron bolts and nuts in metallic structures get rusted. Do you know why these are happening? .
It is because of a reaction called oxidation
oxidation
The chemical reaction which involves addition of oxygen or removal of hydrogen or loss of electrons is called
Reduction
: The chemical reaction which involves addition of hydrogen or removal of oxygen or gain of electrons is called reduction
oxidation-reduction reactions or Redox reactions
the oxidation and reduction occurs in the same reaction (simultaneously). If one reactant gets oxidised, the other gets reduced. Such reactions are called .
Substances which have the ability to oxidise other substances are called _____
oxidising agents
oxidising agents are also called as electron acceptors .
because they remove electrons from other substances
Substances which have the ability to reduce other substances are called
Reducing agents.
Reducing agents are also called as electron donors
because they donate electrons to other substances.
The oxidation reaction in food materials that were left open for a long period is responsible for spoiling of food. This is called .
Rancidity
_______ of an element is defined as the formal charge which an atom of that element appears to have when electrons are counted.
Oxidation number
Oxidation number(ON) also called
oxidation state is the total number of electrons that an atom either gains or losses in order to form a chemical bond with another atom
sum of oxidation numbers of all the atoms in the formula for a neutral compound is
ZERO
The sum of oxidation numbers of an ion is the ____ as the charge on that ion.
same
Negative oxidation number in compounds of two unlike atoms is assigned to the more _____
electronegative atom.
____ is the tendency of an ator in a molecule to attract towards itself the shared pair of electrons.
ectronegativity
Oxidation number of K and Br in KBr molecule is_____ respectively
+1 and -1
Oxidation number of N in NH, molecule is.
-3
Oxidation number of H is +1 (except hydrides).
Oxidation number of oxygen in most cases is-2.
Oxidation Number of H and O in H_{2}O
H=+1
O= -2
Oxidation Number of S in H_{2}SO_{4}
H2+ s + o4
2x(+1) + x +4(-2)=0
S is +6
Oxidation Number of Cr in K_{2}Cr_{2}O_{7}
K2 + cr2 + o7
2(+1)+2x+7×(-2)=0
ON of cr is +6
Oxidation Number of Fe in FeSO
Fe is +2
Find the oxidation number of Mn in KMnO4
Mn is +7
Find the oxidation number of Cr in Na,cr₂O7
+6
Find the oxidation number of Cu in CuSO4
+2
Find the oxidation number of Fe in FeO
+2
_____ for an atom consists of the symbol of the element surrounded by dots representing the electrons of the valence shell of the atom.
The Lewis dot structure or electron dot symbol
An ionic bond is formed by the electrostatics attraction between positive and negative ions. It is also called as .
Electrochemical bond
Number of valence electrons in carbon is
a) 2
b 4
c) 3
d) 5
4
Sodium having atomic number 11, is ready to_________ electron/ electrons to attain the nearest noble gas electronic configuration.
a) gain one
b) gain two
C) lose one
d) lose two
Lose 1
The element that would form anion by gaining electrons in a chemical reaction is
a) potassium
c) fluorine
b) calcium
d) iron
Fluorine
Oxidising agents are also called as because they remove electrons form other substances.
a) electron donors
b) electron acceptors
electron acceptors
The property which is characteristics of an Ionic compound is that
a. it often exists as gas at room temperature.
b) it is hard and brittle.
c. it undergoes molecular reactions.
d. it has low melting point.
b) it is hard and brittle
. Identify the following reactions as oxidation or reduction
a. Na → (Na +) +( e-)
b. Fe³+ +. 2e- → Fe+
A) oxidation
B) reduction
Identify the compounds as Ionic/ Covalent/Coordinate based on the given characteristics.
a. Soluble in non polar solvents
b. Undergoes faster/instantaneous reactions
c. Non conductors of electricity
d. Solids at room temperature
(a) Co-ordinate Covalent compound.
(b) Ionic compound.
(c) Covalent compound.
(d) Ionic compound.
Question 2.
Give an example for each of the following statements.
(a) A compound in which two Covalent bonds are formed.
(b) A compound in which one ionic bond is formed.
(c) A compound in which two Covalent and one Coordinate bond are formed.
(d) A Compound in which three covalent bonds are formed.
(e) A compound in which a coordinate bond is formed.
Answer:
(a) Oxygen molecule (O2) (O = O)
(b) Sodium’Chloride (NaCl)
(c) Carbon monoxide?
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 1i
(d) Nitrogen molecule (N2) (N ≡N)
(e) NH3 → BF3
Answer:
(a) Oxygen molecule (O2) (O = O)
(b) Sodium’Chloride (NaCl)
(c) Carbon monoxide?
(d) Nitrogen molecule (N2) (N ≡N)
(e) NH3 → BF3
Identify the incorrect statement and correct them.
(a) Like covalent compounds, coordinate compounds also contain charged particles (ions). So they; are good conductors of electricity.
(b) Ionic bond is a weak bond when compared to Hydrogen bond.
(c) Ionic or electrovalent bonds are formed by the mutual sharing of electrons between atoms.
(d) Loss of electrons is called Oxidation and gain of the electron is called Reduction.
(e) The electrons which are not involved in bonding are called valence electrons.
.
Answer:
(a) Incorrect statement. Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(b) Incorrect statement. An ionic bond is a strong bond when compared to a hydrogen bond.
(c) Incorrect statement. Covalent bonds are formed by the mutual sharing of electrons between atoms, (or) Ionic or electrovalent bonds are formed by the transfer of electrons between atoms.
(d) Correct statement
(e) Incorrect statement. The electrons which are not involved in bonding are called lone pair of electrons
Question 5.
Find the oxidation number of the elements in the following compounds.
(a) C in CO2
(b) Mn in MnSO4
(c) N in HNO3
Answer:
(a) C in CO2
1(C) + 2(0) = 0
1x + 2(-2) = 0
x-4 = 0 ‘
x = +4 .
ON of C in CO2 is +4
(b) Mn in MnSO4
1 (Mn) + 1 (S) + 4(0) = 0
x + 1(+6) + 4(-2) = 0
x + 6 – 8 = 0
x – 2 = 0
x = +2
ON of Mn in MnSO4 is +2,
(c) N in HNO3
1(H) + 1 (N) +3(0) =0
1 (+1) + 1 (x) + 3 (-2) =0
+ 1 + x – 6 =0
x – 5 =0
x = +5
ON of N in HNO3 is + 5.
