Chemistry FBISE SSC-1 Keybook Chapter 4

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  1. Why do atoms react?

Ans.     Atoms other than the noble gases have a tendency to react with other elements. Atoms react because they tend to gain stability by losing or gaining electrons. When atoms gain or lose electron they acquire the configuration of next noble gas and become stable.

 

  1. Why noble gases are stable?

Ans.     Noble gases are stable because their valence shells are completed with two or eight electrons. They do not require more electrons to attain stability.

 

  1. Find the number of valence electrons in the following atoms using the periodic table.

Ans.

 AtomGroupValence electron
(a)CarbonIV A4
(b)MagnesiumII A2
(c)PhosphorusV A5

 

  1. Find the number of electrons in valence shell of the following atoms using the periodic table.

Ans.

AtomGroupValence electron
SiliconIV A4
SulphurVI A6
BromineVII A7
ArgonVIII A8
PotassiumI A1
NitrogenVA5

 

  1. Describe the formation of Na+ and Mg+2

Ans.     Na+

Sodium belongs to Group IA on the periodic table. It has only one electron in the valence shell. Sodium atom loses its valence electron and is left with an octet. Represent this by drawing the complete electronic configuration or using an electron dot structure.

Na        1s2 2s2 2p6 3s1                       Na+   1s2 2s2 2p6

This can also represented by following electron dot structure

Mg+2

Magnesium belongs to Group IIA in the periodic table. It has two valence electrons. Magnesium atoms lose these electrons to achieve noble gas configuration. Represent this by drawing the complete electronic configuration or using an electron dot structure. This number also corresponds in the Group number in the periodic table.

Mg       1s2 2s2 2p6 3s2   Mg+2   1s2 2s2 2p6

This can also represented by electron dot structure.

 

 

 

  1. Describe the formation of cations for the following metal atoms.

(a)        Li (atomic No. 3)

Lithium belongs to Group I A. It has only one electron in the valence shell. Lithium atom loses its valence electron and is left with duplet.

Li         1s2 2s1                        Li+   1s2

 

            Al (atomic No. 13)

Aluminum belongs to Group III A. It has three electron in the valence shell. Aluminum atom loses these electrons and is left with octet.

Al        1s2 2s2 2p6 3s2 3p1    Al+3 1s2 2s2 2p6

 

 

  1. Represent the formation of cations for the following metal atoms using electron dot structures.

(a) K    (b) Ca

 

(a)        Formation of K+ ion:

Since K atom has one electron in the outer most shell. It losses one electron to form K+ ion.

(b)        Formation of Ca+2 ion:

Since Ca atom has two electrons in the outer most shell. It losses two electrons to form Ca+2 ion.

 

 

Example 4.3:

Describe the formation of anions for the following non-metal atoms:

Solution:

  • Formation of anion by oxygen atom:

Oxygen belongs to Group VIA on the periodic table. So it has six electrons in its valence shell. It needs two electrons to achieve noble gas configuration.

O         1s2 2s2 2p4 + 2ē          O-2 1s2 2s2 2p6                             

We can also represent this by electron dot structure

 

  • Formation of anion by fluorine atom

Fluorine belongs to Group VIIA on the periodic table. So it has seven electrons in the valence shell. A fluorine atom therefore, requires only one electron to complete octet.

 

F          1s2 2s2 2p5 + ē    F 1s2 2s2 2p6

 

We can also represent this by electron dot structure.

 

  1. Describe the formation of anions by the following non-metals

(a)        Sulphur (atomic No. 16)

Sulphur belongs to Group VI A. It has six electrons in valence shell, it gain two electrons to complete octet. So it gains two electron to form S-2 ion.

 

S          1s2 2s2 2p6 3s2 3p4+2ē    S-2 1s2 2s2 2p6 3s2 3p6

 

(b)        Chlorine (atomic No. 17)

Chlorine belongs to Group VII A. It has seven electrons in valence shell. It gain one electron to complete octet.

 

Cl         1s2 2s2 2p6 3s2 3p5+1ē    Cl-1 1s2 2s2 2p6 3s2 3p6

  1. Represent the formation of anions by the following non-metals using electron dot structures.

(a)        N:

Nitrogen belongs to Group VA. It has five electrons in valence shell. It gains three electrons to complete octet.

(b)        P:

Phosphorus belong to Group VA. It has five electrons in valence shell. It gains three electrons to complete octet.

 

 

(c)        Br:

Bromine belongs to Group VIIA. It has seven electrons in valence shell. It gains one electrons to complete octet.

 

(d)        H:

Hydrogen belongs to Group IA. It has one electron in valence shell. It gains one electron to complete duplet.

 

 

Example 4.4:

For each of the following pairs of atoms, use electron dot and electron cross structures to write the equation for the formation of ionic compound.

  • Na and Cl

Na is metal and Cl is non-metal. Na atom has one electron in its outermost shell. It loses one electron to form Na+ ion. Since Cl atom has seven electrons in outermost shell, so it gains one electron to form Clion.

For every Na+ ion we need one Cl ion.

  • Mg and F:

Mg is metal and F is non-metal. Mg atom has two electrons in its outermost shell. It loses two electrons to form Mg+2 ion. Since F atom has seven electrons in outermost shell, so it gains one electron to form Fion.

For every Mg+2 ion we need two F ions.

 

For each of the following pair of atoms, use electron dot and electron cross structures to write the equation for the formation of ionic compound.

  • Mg and O

Mg is metal and O is non-metal. Mg atom has two electrons in its outermost shell. It loses two electrons to form Mg+2 ion. Since O atom has six electrons in outermost shell, so it gains two electrons to form O-2 ion.

For every Mg+2 ion we need one O-2 ion.

  • Al and Cl:

Al is metal and Cl is non-metal. Al atom has three electrons in its outermost shell. It loses three electrons to form Al+3 ion. Since Cl atom has seven electrons in outermost shell, so it gains one electron to form Clion.

For every Al+3 ion we need one Cl ion.

Example 4.5:

Recognize the following compounds as having ionic bonds.

  • Mg and O:

Mg is metal and O is non-metal. Mg atom has two electrons in its outermost shell. It loses two electrons to form Mg+2 ion. Since O atom has six electrons in outermost shell, so it gains two electrons to form O-2 ion. In this way, both the atoms will acquire nearest noble gas configuration. For every Mg+2 ion we need one O-2 ion. Final resulting compound will be MgO.

  • Na and F:

Na is metal and F is non-metal. Na atom has one electron in its outermost shell. It loses one electron to form Na+ ion. Since F atom has seven electrons in outermost shell, so it gains one electron to form Fion. In this way both the electrons will acquire stable nearest noble gas electronic configuration.

For every Na+ ion we need one F ion. Resulting compound will be NaF.

 

Recognize the following compounds as having ionic bonds.

  • KCl:

K is metal and Cl is non-metal. K atom has one electron in its outermost shell. It loses one electron to form K+ ion. Since Cl atom has seven electrons in outermost shell, so it gains one electron to form Clion. In this way both the atoms acquire electronic configuration of nearest noble gas by losing or gaining electrons.

For every K+ ion we need one Cl ion. Thus, KCl is an ionic compound.

  • AlCl3:

Al is metal and Cl is non-metal. Al atom has three electrons in its outermost shell. It loses three electrons to form Al+3 ion. Since Cl atom has seven electrons in outermost shell, so it gains one electron to form Clion. In this way both the atoms acquire electronic configuration of nearest noble gas by losing or gaining electrons.

For every Al+3 ion we need three Cl ion. Thus AlCl3 is an ionic compound.

  • MgF2:

Mg is metal and F is non-metal. Mg atom has two electrons in its outermost shell. It loses two electrons to form Mg+2 ion. Since F atom has seven electrons in outermost shell, so it gains one electron to form Fion. In this way both the atoms acquire electronic configuration of nearest noble gas by losing or gaining electrons.

For every Mg+2 ion we need two F ions. Thus MgF2 is an ionic compound.

 

  1. Explain formation of covalent bond between F atoms:

Consider the formation of a bond between two fluorine atoms. Fluorine belongs to group VIIA, so it has seven electrons in the valence shell. It needs one more electron to attain the electronic configuration of nearest noble gas. Thus two F atoms share an electron pair and achieve electronic configuration of Neon. For sharing each F atom contributes one electron to complete the octet.

or

  1. Differentiate between ionic and covalent bond.
Ionic BondCovalent Bond
1.   It is formed by the complete transfer of electrons from one atom to the other.It is formed by the mutual sharing of equal number of electrons between two atoms.
2.   It is indicated by positive and negative charges.It is represented by a small straight line.
3.   Examples: NaCl, CaCl2, K2O, MgOExamples: H2, Cl2, O2, N2

 

Example 4.6:

Draw electron cross and dot structures for:

  • CH4:

C has four electrons in the valence shell and needs four electrons to complete its octet. H has only one valence electron and needs one electron to complete duplet. So C can form four single bonds with four H-atoms. C is the central atom.

or

  • H2O:

O has six electrons in the valence shell and needs two electrons to complete its octet. H has only one valence electron and needs one electron to complete duplet. So O can form two single bonds with two H-atoms. O is the central atom.

or                  

            Draw electron cross and dot structures for the following molecules.

(a)        NH3 that is used to manufacture urea.

N has five electrons in its valence shell and needs three electrons to complete its octet. H has only one electron and needs one electron to complete its duplet. So, N can form three single bonds with H atoms. N is the central atom.

(b)        CCl4 dry cleansing agent.

C has four valence electrons and needs four electrons to complete its octet. Chlorine has seven valence electrons and need one electron to complete its octet. So C can form four single bonds with Cl atom. C is the central atom.

(c)        SiCl4 used to make smoke screens.

Si has four valence electrons and needs four electrons to complete its octet. Cl has seven valence electrons and need one electron to complete its octet. So Si will form four single bonds with four Cl atoms. Si is the central atom

 

(d)        H2S a poisonous gas

S has six valence electrons and needs two electrons to complete its octet. H has one electron and needs one more electron to complete its duplet. S will form two single bonds with two H atoms. S is the central atom

 

Example 4.7

            Draw electron cross and dot structures for the following molecules.

 

(a)        CO2 a component of air and is responsible for greenhouse effect.

C has four electrons in the valence shell. It needs four electrons to complete octet. Oxygen atom has six valence electrons and needs two electrons to have an octet. C is central atom. Since C needs four electrons. So it will share its two electrons with each oxygen atoms.

 

 

(b)        HCN, used as insecticide

H has one, C has four and N has five electrons. C needs four and N needs three electrons. So C share one electron with H to form a single bond and three electrons with N to form a triple bond. This will satisfy octet rule.

 

            Draw electron cross and electron dot structures for the following molecules.

 

(a)        CS2 an organic solvent that dissolves Sulphur, Phosphorus etc.

C has four electrons in the valence shell. It needs four electrons to complete octet. S has six electron in valence shell and need two electron to complete octet. C is central atom. So C can form two double bonds with S.

or

(b)        N2 a component of air

N has five electrons in the valence shell. It needs three more electrons to complete octet. So for sharing each N atom contributes three electrons.

or

 

 

  1. What is non-polar covalent bond?

Ans.     When two identical atoms share electron pairs, both the atoms exert some force on the shared electron pairs. Such a covalent bond is called non-polar covalent bond.

 

  1. What is polar covalent bond?

Ans.     Polar covalent bond is bond in which electrons are shared unequally between two atoms. Thus one atom bears partial positive charge and the other a partial negative charge.

 

  1. What are dipole-dipole forces?

Ans.     When slightly negative end of polar molecule is weakly attracted to the slightly positive end of another molecule. Such attracting forces are called dipole-dipole forces.

 

 

  1. Define hydrogen bonding? Draw hydrogen bonding in water molecule?

Ans.     The interaction of a highly electron deficient hydrogen and lone pair on a nearby highly electronegative atom such as N, O or F is called hydrogen bond.

 

  1. What is importance of intermolecular forces?

Ans.                 The intermolecular forces are extremely important in determining properties of water, biological molecules, such as proteins, DNA etc and synthetic materials such as glue, paints, resins etc.

 

  1. Discuss the arrangement of ions:

(a)        NaCl:

Each Na+ ion is surrounded by six Cl ions and each Cl ion is surrounded by six Na+ ion.

 

(b)        CsCl

Each Cs+ ion is surrounded by eight Cl ions and each Cl ion is surrounded by eight Cs+ ion.

 

Review Questions

Q.1      Encircle the correct answer:

  • Which of the following atoms will form an ion of charge -2 ?

Atomic Number       Mass Number

  1. 12 24
  2. 14 28
  3. 8 8
  4. 10                        20
  • Which of the following atoms will not form cation or anion.
  1. A (Atomic No. 16)
  2. B (Atomic No.. 17)
  3. C (Atomic No. 18)
  4. D (Atomic No. 19)
  • Which of the following atoms will form cation.
  1. 20 18    c. 17    d. 15
  • Which of the following atoms obey duplet rule?
  1. O2 F2 c. H2   d. N2
  • Silicon belongs to Group IV A. It has ____ electrons in the valence shell
  1. 2   b. 3     c. 4   d. 6
  • Phosphorus belongs to third period of Group VA. How many electrons it needs to complete its valence shell.
  1. 2     b. 3       c. 4       d. 5
  • In the formation of AlF3, aluminum atom loses ____ electrons.
  1. 1 2      c. 3      d. 4
  • Which of the following is not true about the formation of Na2S:
  1. Each sodium atom loses one electron
  2. Sodium forms cation
  3. Sulphur forms anion
  4. Each sulphur atom gains one electron
  • Identify the covalent compound
  1. NaCI MgO          c.H20     d. KF

 

Answers:

1.      B2.      B3.      D4.      C5.      C
6.      B7.      D8.      D9.      B 

 

 

Q.2      Give short answers

(i)         State octet and duplet rules

Ans.     Octet rule:

The tendency of atoms to acquire eight electron configuration in their valence shell, when bonding is called octet rule.

Duplet rule:

The tendency of some atoms to acquire two electron configuration in their valence shell, when bonding is called duplet rule.

 

(ii)        Explain formation of covalent bond between two nitrogen atoms.

Ans.                 Nitrogen is in Group VA. So it has 5 electrons in the valence shell. It requires 3 more electron to complete octet. So for sharing each N-atom contributes three electrons.

or

 

(iii)       How does Al form cation?

Ans.     Al atom has three electrons in the outer most shell, it losses three electron to complete octet.

Al        1s2 2s2 2p6 3s2 3p1 Al+3 1s2 2s2 2p6

 

(iv)       How does O form anion?

Ans.     Oxygen belongs to group VIA. So it has six electrons in its valence shell. It requires two electrons to complete noble gas configuration

O         1s2 2s2 2p4 +2e O-2 1s2 2s2 2p6

 

(v)        Draw electron cross and dot structure for H2O molecule.

Ans.     Oxygen has six valence electrons and hydrogen has one valence electron. Oxygen needs two electrons to complete octet and each hydrogen needs one electron to complete duplet. Oxygen is central atom and will form two single bonds with H-atoms.

 

or

 

Q.3      Describe the importance of noble gas electronic configuration

Ans.     An element which does not have two or eight electrons in its valence shell is unstable. It get stability by losing, gaining or sharing electron to complete noble gas electronic configuration.

 

Q.4      Explain how elements attain stability.

Ans.     Elements attain stability by completing duplet or octet. Atoms gains loss or share electrons to complete duplet or octet, and become stable.

 

Q.5      Describe the ways in which bonds may be formed?

Ans.     There are two main ways:

  • Ionic Bond:

Ionic Bonds are formed between two atoms, when one atom loses electron to form cation and the other atom gains this electron to form anion.

Or

Ionic Bonds are formed due to complete transfer of electron from one atom to another atom.

  • Covalent Bond:

A covalent bond is formed by mutual sharing of electrons between two atoms.

 

Q.6      Describe the formation of covalent between two non-metallic elements.

Ans.     Consider the formation of covalent bond in hydrogen molecule. A hydrogen atom has a single valence electron. Two hydrogen atoms share their valence electron to form diatomic molecule.

 

H + H   H : H

 

Q.7      Explain with examples single, double and triple covalent bond.

Ans:     Single Covalent Bond:

Covalent bond that is formed by the sharing of one electron pair is called single covalent bond.

            Example:

Consider the formation of covalent bond in hydrogen molecule. A hydrogen atom has single valence electron. Two hydrogen atom share their valence electrons to form a diatomic molecule.

H + H   H : H or H – H

Double Covalent Bond:

Double covalent bonds are formed by sharing of two electron pairs.

Examples:

Consider the formation of O2 molecule. Oxygen is in Group VI A, so it has 6 electrons in the valence shell. It requires two more electron to complete its octet. So for sharing each O-atom contributes two electrons.

 

 

Or

 

Triple Covalent Bond

Triple covalent bonds are formed by sharing of three electrons pairs.

            Examples:

Nitrogen is in Group VA. So it has five electrons in the valence shell. It requires three more electron to complete octet. So for sharing each N-atom contributes three electrons.

 

Or

 

Q.8      Find the number of valence electrons in the following atoms using the periodic table.

Ans.     Element           Group              Valence electrons

(a)        Boron              III A                             3

(b)        Neon                VIII A                          8

(c)        Rubidium         I A                               1

(d)        Barium             II A                              2

(e)        Arsenic                        VA                               5

 

Q.9      Represent the formation of cations for the following metal atoms using electron dot structures.

(a)        Al (atomic number = 13)

Al atom has three electrons in the outer most shell, it losses three electron to complete octet.

Al        1s2 2s2 2p6 3s2 3p1 Al+3 1s2 2s2 2p6 + 3e

 

 

  • Sr (atomic number = 18)

Sr atom has two electrons in the outermost shell. it loses two electrons to complete octet.

Sr 1s22s22p63s23p63d104s24p65s2 Sr+2 1s22s22p63s23p63d104s24p6 +2e

  • Ba (atomic number = 56)

Ba atom has two electrons in the outermost shell. it loses two electrons to complete octet.

Ba:1s22s22p63s23p63d104s24p64d105s25p66s2 Ba+2   :1s22s22p63s23p63d104s24p64d105s25p6 +2e

Q.10    Describe the formation of anions for the following non-metals atoms:

 

  • P (atomic number = 15)

P atom has five electrons in outermost shell, it gains three electrons to complete its octet and become P-3 ion.

 

  • Br (atomic number = 35)

Br atom has seven electrons in outermost shell, it gains one electron to complete its octet and become Br-1 ion.

 

  • H (atomic number = 1)

H atom has one electron in outermost shell, it gains one electron to complete its octet and become H-1 ion.

 

Q.11    Represent the formation of cations for the following metal atoms using electron dot structures.

 

(a)        Mg (atomic number = 12)

 

(b)        Li (atomic number = 3)

(c)        Be (atomic number = 4)

Q.12    For each of the following pairs of atoms use electron dot and electron cross structures to write the equation for the formation of ionic compound.

 

  • K and Cl

K is metal and Cl is non-metal.

Metal atom tends to lose electrons and non-metal atoms tends to gain electrons to acquire electronic configuration of nearest noble gas. Since K atom has one electron in the outermost shell. It losses one electron to form K+ ion. Since Cl has seven electrons in outermost shell, it needs one electron to complete octet. So it gains one electron to form Cl ion. For every K+ ion, we need one Cl ion.

 

 

  • Ca and S:

Ca is metal and S is non-metal. Ca atom has two electrons in outermost shell. It loses two electrons to form Ca+2 ion. Since S atom has six electrons in outermost shell, so it gains two electrons to complete its octet and form S-2 ion.

Therefore, we need one S-2 ion for every Ca+2 ion.

  • Al and N

Al atom has three electrons In outermost shell. It loses three electrons to form Al+3 ion. Since, N atom has five electrons in outermost shell, so it gains three electrons to form N-3 ion. For every Al+3 ion we need N-3 ion.

Q.13    Recognize the following compounds as having ionic bonds.

  • MgCl2

Mg is metal and Cl is non-metal. Mg atom has two electrons in its outermost shell. it loses two electrons to form Mg+2 ion, Since Cl atom has seven electrons in outermost shell, so it gains one electron to form Cl ion. For every one Mg+2 ion, we will need 2 Clions.

  • KBr:

K is metal and Br is non-metal. Metal atom tends to lose electrons and non-metal atoms tends to gain electrons to acquire electronic configuration of nearest noble gas. Since K atom has one electron in the outermost shell. It losses one electron to form K+ ion. Since Br has seven electrons in outermost shell, it needs one electron to complete octet. So it gains one electron to form Br ion. For every K+ ion, we need one Br ion.

  • NaI:

Na is metal and I is non-metal. Metal atom tends to lose electrons and non-metal atoms tends to gain electrons to acquire electronic configuration of nearest noble gas. Since Na atom has one electron in the outermost shell. It losses one electron to form Na+ ion. Since I has seven electrons in outermost shell, it needs one electron to complete octet. So it gains one electron to form I ion. For every Na+ ion, we need one I ion.

 

 

Q.14    An atom of an element has atomic number 9 and mass number 19

(a)        State the number of protons and neutrons in the nucleus of this atom.

Ans.     Number of protons = atomic number = 9

Number of neutrons = atomic mass – atomic number

= 19-9 = 10

 

(b)        State the number of electrons in this atom

Ans.     Number of electrons = atomic number = 9

 

(c)        Show with electron cross dot diagrams, the formation of ions in the reaction of this atom with sodium atom.

Ans.     Element is fluorine because atomic number = 9

Since Na is metal and F is non-metal. Metal atoms tends to lose electrons and non-metal atoms tends to gain electrons to acquire electronic configuration of nearest noble gas. Na atom has one electron in the outer most shell. It losses one electron to form Na+ ion. F atom has seven electrons in outermost shell, it needs one electron to complete octet. So it gains one electron to form F ion. For every Na+ ion, we need one F ion.

 

Q.15    Is there a need for more adhesives?

Ans.     Yes there is a need for more adhesives because they have excellent chemical resistance, good adhesion properties, good heat resistance and they form strong and tough coating. Adhesives become an essential item in our daily life.

 

Q.16    What is the importance of glues and adhesives in our society?

Ans.     Glues and adhesives are used in large scale industrial applications. Glues are used in paper making. Glues are also used for joining glass and metals. Adhesives are used where water resistance is required. Therefore, dams, bridges, thermal power stations are coated with resins. They are also used in paints.

 

ThinkTank

 

  1. Magnesium oxide is a compound made up of magnesium ions and oxide ions.
  • What is the charge on these ions?

Ans.   Mg+2 and O-2

  • How these ions get these charges?

Ans.   Magnesium loses two electrons and become Mg+2 ion.

Oxygen gains two electrons and become O-2

  • Show with electron cross-dot diagrams the formation of these ions.

Ans.   Formation of Mg+2 ion

Mg: 1s22s22p63s2                      Mg+2: 1s22s22p6

We can also represent this by electron dot structure.

Formation of O-2 ion:

O: 1s22s22p4+2e                 O-2: 1s22s22p6

  1. The diagrams below show the electronic structures of an atom of calcium and an atom of oxygen.

Draw structures of the ions that are formed when these atoms react.

  

  1. Draw electron cross and dot structure for the following molecules:
  • COCl2, a poisonous gas called phosgene that has been used in World War-II.
  • HOCl, hypochlorous acid is unstable, decomposes to liberate atomic oxygen that makes HoCl a strong oxidizing agent.
  1. The table below shows the properties of four substances
SubstanceMelting PointElectrical Conductivity
In Solid StateIn Molten State
AHighNILNIL
BHighNILGood
CLowNILNIL
DHighGoodGood
  • Which substance is a metal?

Ans.   Substance D is a metal because metal conducts electricity in solid or molten state and also has high melting points.

  • Which Substance is an ionic compound?

Ans.   Substance B is an ionic compound because ionic compounds do not conduct electricity in solid state but are good conductors of electricity in molten state. They also have high melting points (e.g. NaCl).

  • Which substance is covalent bond?

Ans.   Substance C is a covalent compound because it do not conduct electricity in solid or molten state and has low melting point.

  • Which substance is a non-metal?

Ans.   Substance A is a non-metal which has high melting point and is non-conductor of electricity in solid or molten state. (e.g. allotropic form of carbon; diamond)

  1. Electronic configuration of two elements X and Y are given below:

X=1s22s22p63s2

Y=1s22s22p4

Which of the following compounds is likely to form when X and Y react?

  • A covalent compound of formula XY2
  • An ionic compound of formula XY2
  • An ionic compound of formula XY
  • A covalent compound of formula X2Y

Ans. It will form an ionic compound of formula XY, because X loses two electrons from its valence shell to form X+2, whereas Y gains 2 electrons to complete its octet and form Y-2. So ionic compound of formula XY is formed.

  1. The figure shows the electron dot and cross diagram of molecule AB2. Which of the elements could be A and B?

Ans.       The name of element A is oxygen because it contains six electrons in valence shell. (Group VIA). And the name of element B is chlorine because it contains seven electrons in its valence shell. (Group VIIA)

Element A is oxygen and element B is chlorine. The molecule formed is chlorine monoxide (Br2O). It is also known as oxygen dichloride, dichlorine oxide, or chlorine oxide. It is a brownish yellow gas at room temperature which can explode in high concentrations when exposed to heat or sparks.

 

 

  1. What is the total number of shared electrons in a molecule of CO2?

Ans. The total number of shared electrons in a molecule of CO2= 4+4 = 8