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Download 9th Class Chemistry Notes (Unit # 4) for Federal Board (FBISE) Islamabad

Download 9th Class Chemistry Notes (Unit # 4) for Federal Board (FBISE) Islamabad

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Download 9th Class Chemistry Notes (Unit # 4) for Federal Board (FBISE) Islamabad

State- octet and duplet rules.
Octet rule:
·        The tendency of atoms to acquire eight electron configurations in their valence shell, is called octet rule.
·        Each noble gas (except He) has eight electrons in their valence shell.
Duplet rule:
·        The tendency of some atoms to acquire two electron configurations in their valence shell is called duplet rule.
·        Helium has two electrons in its valence shell and is also chemically inert.
·        Some other elements also tend to achieve two electron configurations in their valence shell. For example Hydrogen, Lithium etc.

Explain formation of covalent bond between two nitrogen atoms.
·        Nitrogen is in Group V-A, so it has 5 electrons in the valence shell.
·        It needs three electrons to complete its octet.
·        So for sharing each N-atom contributes three electrons.
How does Al form cations?
Since Al atom has three electrons in the outer most shell, it losses three electrons to form Al+3 ion.
How does Oxygen form anion?
Oxygen belongs to Group VI-A on the periodic table, so it has six electrons in its valence shell. It needs two electrons to achieve noble gas configuration.
Draw electron cross and dot structure for H2O molecule.
·        O has six valence electrons and each hydrogen atom has one valence.
·        So O-atom needs two electrons to complete octet. Each H needs one electron to complete duplet.

Describe the importance of noble gas electronic configuration.
·        Noble gases usually not combine to other elements or themselves.
·        It is due to their electronic configuration.
·        He has 2 valence electrons while other elements (Ne, Ar, Kr, Xe, Rn) have 8 valence electrons.
·        In all noble gases their valence shell is completely filled.

Explain how elements/atoms attain stability?
·        An atom gains stability by having 8 electrons in its outer shell or 2 in some cases.
·        It can do this through covalent bonding, or ionic bonding etc.
·        If an element has less than 8 electrons it is unstable, and it gets stability by losing, gaining or sharing electrons.

Describe the ways in which bonds may be formed.
·        The two types of bonds are formed between atoms. Ionic and Covalent.
·        An ionic bond is formed when one atom accepts or donates one or more of its valence electrons.
·        A covalent bond is formed when atoms share valence electrons.
·        The atoms do not always share the electrons equally, so a polar covalent bond may be the result.
·        When electrons are shared by two metallic atoms a metallic bond may be formed.

Describe the formation of covalent bond between two non-metallic elements.
Consider the formation of covalent bond in hydrogen molecule. A hydrogen atom has a single valence electron. Two hydrogen atoms share their valence electrons to form a di-atomic molecule.
In the formation of this molecule, each hydrogen atom achieves the electron configuration of the noble gas, helium which has two valence electrons.

Explain with examples single, double and triple covalent bond.
Formation of single covalent bond in hydrogen molecule:
·        Single covalent bonds are the bonds that are formed by sharing of one electron pairs.
·        Consider the formation of covalent bond in hydrogen molecule. A hydrogen atom has a single valence electron. Two hydrogen atoms share their valence electrons to form a di-atomic molecule.
·        In the formation of this molecule, each hydrogen atom achieves the electron configuration of the noble gas, helium which has two valence electrons.
Formation of double covalent bond between two oxygen atoms:
·        Double covalent bonds are the bonds that are formed by sharing of two electron pairs.
·        Consider the formation of O2 molecule. Oxygen is in Group VI-A, so it has 6 electrons in the valence shell. It needs two electrons to complete its octet. So for sharing each O-atom contributes two electrons.
Formation of triple covalent bond between two nitrogen atoms:
·        Triple covalent bonds are the bonds that are formed by sharing of three electron pairs.
·        Consider the formation of N2 molecule, Nitrogen is in Group V-A, so it has 5 electrons in the valence shell. It needs three electrons to complete its octet.
·        So for sharing each N-atom contributes three electrons.

Find the number of valence electrons in the following atoms using the ionic table.
·        Boron (3 electrons group III-A element).
·        Neon (8 electrons group VIII-A element)
·        Rubidium (1 electron group I-A element)
·        Barium (2 electrons group II-A element)
·        Arsenic (5 electrons group V-A element)
Represent the formation of cations for the following metal atoms using electron dot structures.
Al+3, Sr+2, Ba+2
Formation of Al+3 ion: (Atomic number of Aluminum = 13)
Since Al atom has three electrons in the outer most shell. It losses three electrons to
form Al+3 ion.
Formation of Sr+2 ion: (Atomic number of strontium = 38)
Since Sr atom has two electrons in the outer most shell. It losses two electrons to form Sr+2 ion.
Formation of Ba+2 ion: (Atomic number of barium = 56)
Since Ba atom has two electrons in the outer most shell. It losses two electrons to form Ba+2 ion.

Describe the formation of anions for the following non-metal atoms. P, Br, H
Formation of P-3 anion:
Since P atom has five electrons in outermost shell, it needs three electrons to complete octet. So it gains three electrons to form P-3 ion
Formation of Br-1 anion:
Since Sr atom has seven electrons in outermost shell, it needs one electron to complete octet. So it gains one electron to form Br-1 ion.
Formation of H-1 anion:
Since H atom has one electron in outermost shell, it needs one electron to complete duplet. So it gains one electron to form H-1 ion.
Represent the formation of cations for the following metal atoms using electron dot structures. A) Mg b) Li c) Be
Formation of Mg+2 ion. (Atomic number of Magnesium = 12)
Formation of Li+ ion. (Atomic number of lithium = 3) '
Formation of Be+2 ion. (Atomic number of Beryllium = 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.
K and Cl:
Ca and S:

Al and N:

Is there a need for more adhesives?
Yes, there is a need for more adhesive. The adhesive action of paints and dyes is developed due to hydrogen bonding.

What is the importance of glues and adhesives in our society?
·        An adhesive or stick on is a material (natural or synthetic) that adheres or bonds items together.
·        Adhesives cure (harden) by either evaporating a solvent or by chemical reactions that occur between two or more constituents.
·        Adhesives are advantageous for joining thin or dissimilar materials, minimizing weight, and when a vibration-damping joint is needed.
·        A disadvantage of most adhesives is that most do not form an instantaneous joint, unlike many other joining processes, because the adhesive needs time to cure.
·        Resins are widely used to paint dams, bridges, buildings and automobiles.

Why do atoms react?
All atoms (except for the noble gases) are unstable because their outer electron shell is not completely filled. Atoms react with other atoms to gain or lose electrons to fill their outer shell

Define chemical bond?
The chemical force which keeps the atoms together is commonly described a chemical bond.

Define dipole-dipole interacti.ons. What is the nature of these linkages?
Slightly negative end of polar molecule is weakly attracted to the slightly positive end of another molecule. Such attracting forces are called dipole-dipole interactions.  These linkage are weak and temporarily.

What is Hydrogen bonding?
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. This phenomenon is called hydrogen bonding.


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Download Class Notes: Download 9th Class Chemistry Notes (Unit # 4) for Federal Board (FBISE) Islamabad
Download 9th Class Chemistry Notes (Unit # 4) for Federal Board (FBISE) Islamabad
Download 9th Class Chemistry Notes (Unit # 4) for Federal Board (FBISE) Islamabad
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