Chemical Bonding Flashcards
What is a chemical bond?
Chemical bond is the force which holds two or more atoms together in a stable molecule
What is an atom?
An atom is the smallest unit of matter taking part in a chemical reaction
What is an atom built up of?
Sub-atomic particles - protons, neutrons, electrons
What combines to forma molecule?
Two or more atoms (metallic or non-metallic)
What are elements?
They are pure substances made up of one kind of atoms having the same atomic number
Name the type of atoms involved in chemical combination
- Metallic Elements
2. Non-metallic elements
Give the no. of valence electrons in the valence shell of a metallic atom
They have 1, 2, 3 electrons in the valence shell
What is the nature of metallic ions?
Metallic ions become positively charged ions (cations) because they lose 1, 2, or 3 electrons to attain stable electronic configuration
Give the no. of valence electrons in the valence shell of a non-metallic atom
They have 4, 5, 6, or 7 electrons in their valence shell
What is the nature of non-metallic ions?
They gain (4), 3, 2, or 1 electrons and become negatively charged ions (anions)
Name the two means by which atoms combine to form a molecule
- Transfer of valence electrons from a metallic atom to a non-metallic atom
- Sharing of valence electrons between two atoms (generally both non-metallic)
Give the mass of a proton
1 a.m.u [C-12 standard]
Give the mass of an electron
negligible
Give the mass of a neutron
1 a.m.u [C-12 standard]
Why are noble gases inert or unreactive?
They have stable electronic configuration i.e. their valence shell is complete. They have 2 electrons in the outermost shell [He] or 8 electrons in the outermost shell. Therefore, they do not lose, gain or share electrons.
Why are atoms of other elements other than noble gases chemically reactive?
They have unstable electronic configuration. They can lose, gain or share electrons because their outermost shell is incomplete.
What is the reason for chemical bonding between atoms?
The driving force for atoms to combine is the tendency of each atom to attain a stable electronic configuration of the nearest noble gas
What is duplet rule?
Two electrons in the valence shell
What is octet rule?
8 electrons in the valence shell
Name the periodic properties that affect bond formation of an ionic or covalent compound
- Ionisation Potential
- Electronaffinity
- Electronegativity
How does IP affect the formation of an ionic bond?
Lower the value of IP of a metallic atom, greater the ease of formation of the cation
How does electronaffinity affect the formation of an ionic bond?
Higher the value of E.A. of a non-metallic atom, grater the ease of formation of the anion
How does E.N. affect the formation of an ionic bond?
Larger the E.N. difference between combining atoms, electron transfer takes place easily
Name the factors which affect the formation of a covalent bond
- I.P. should be high between both atoms/elements
- E.A. should be high between both atoms/elements
- E.N. should be high between both atoms/elements
- E.N.D should be negligible between the two combining atoms
How does formation of electrovalent compounds take place?
It involves transfer of valence electrons from one atom generally metallic to another atom - generally non-metallic
Give the equation for a metallic atom losing electrons in ionic bonding
X [elec. config. 2,8,1]
X - 1e- –> X 1+ Cation (positive ion 2,8)
Give the equation for a non-metallic atom gaining electrons in ionic bonding
Y [elec. config. 2,8,7]
Y + 1e- –> Y 1- Anion (negative ion 2,8,8]
What are cations and anions?
They are oppositely charged particles, which attract one another to form an electrovalent bond leading to the formation of an electrovalent compound.
What is electrovalent bond formation due to?
Electrostatic force of attraction between two oppositely charged ions
Define ionic bond
The chemical bond formed between two atoms by transfer of one or more electrons from the atom of a metallic - electropositive element to an atom of a non-metallic - electronegative element
Define ionic compound
The chemical compound formed as a result of transfer of one or more electrons from the - atom of a metallic -electropositive element to an - atom of a non-metallic - electronegative element
Define electrovalency
The number of atoms donated or accepted by the valence shell of an atom of an element - so as to achieve stable electronic configuration
Differentiate between atoms X and Y vs ions X and Y on the basis of nature
Atoms X and Y - electrically neutral particles, whereas ions X 1+ and Y 1- are electrically charged particles (cations, anions)
Differentiate between atoms X and Y vs ions X and Y on the basis of existence
Atoms X and Y may or may not exist independently, whereas ions X 1+ and Y 1- exist independently in solution
Differentiate between atoms X and Y vs ions X and Y on the basis of valence shell
In atoms X and Y, outermost shell may or may not have duplet or octet, whereas ions X 1+ and Y 1- have complete duplet and octet
What happens to an atom or ion during oxidation?
It loses electrons
What happens to an atom or ion during reduction?
It gains electrons
Give an alternative form of the equation X - 1e- –> X 1+
X –> X 1+ + 1e-
How is a sodium compound formed?
As a result of transfer of one valence electron from metallic sodium atom [At. No. 11 - 2,8,1] to a non-metallic chlorine atom [At. No. 17 - 2,8,7]
How does sodium attain s.e.c in the formation of sodium chloride?
Sodium atom attains s.e.c of the nearest noble gas - Neon by losing one electron from its valence shell and becomes a positively charged sodium ion (cation) - Na 1+
How does chlorine attain s.e.c in the formation of sodium chloride?
Chlorine atom attains s.e.c of the nearest noble gas - Argon by gaining one electron in its valence shell and becomes a negatively charged chlorine ion (anion) - Cl 1-
Give examples of the ionic bonds sodium and chloride from with other elements
- K [At. No. 19] and Cl [At. No. 17] form KCl - Potassium chloride
- Na [At. No. 11] and S [At. No. 16] form Sodium sulfide - Na2S
Give the ionic equation for the formation of sodium chloride
Na - 1e- –> Na 1+ [oxidation]
Cl + 1e- –> Cl 1- [reduction]
Na + Cl –> Na 1+ Cl 1- –> NaCl
How is calcium oxide formed?
It is formed as a result of transfer of two valence electrons from metallic calcium atom [At. No. 20 - 2,8,8,2] to non-metallic oxygen atom [At. No. 8 - 2,6]
How does calcium attain s.e.c in the formation of calcium oxide?
Calcium atom attains s.e.c of the nearest noble gas - Argon by losing two electrons from its valence shell and becomes a positively charged calcium ion (cation) - Ca 2+
How does oxygen atom attain s.e.c in the formation of calcium oxide?
Oxygen attains s.e.c of the nearest noble gas Neon by gaining two electrons in its valence shell and becomes a negatively charged oxide ion (anion) - O 2-
Give the ionic equation of the formation of CaO
Ca - 2e- –> Ca 2+ [oxidation]
O + 2e- –> O 2- [reduction]
Ca + O –> Ca 2+ + O 2- –> CaO
How is magnesium chloride formed?
It is formed as a result of transfer of two valence electrons from one metallic magnesium atom [At. No. 12 - 2,8,2] to two non-metallic chlorine atoms [At. No. 17 - 2,8,7]
How does magnesium atom attain s.e.c in the formation of magnesium chloride?
Magnesium atom attains s.e.c of the nearest noble gas Neon by losing two electrons from its valence shell and becomes a positively charged magnesium ion (cation) - Mg 2+
How does chlorine atom attain s.e.c in the formation of magnesium chloride?
Chlorine atom attains stable electronic configuration of the nearest noble gas argon by gaining one electron in its valence shell and becomes a negatively charged chloride ion [anion] - Cl-
How does the transfer of electrons take place in the formation of magnesium chloride?
Magnesium atom donates two electrons [is oxidised], whereas chlorine atom accepts only one electron [is reduced] to give chlorine ion. Thus, to accept another magnesium atom, there must be another chlorine atom
Give the ionic equation of the formation of MgCl2
Mg - 2e- –> Mg 2+ [oxidation]
2Cl + 2e- –> 2Cl- [reduction]
Mg + 2Cl –> Mg 2+ 2Cl 1- –> MgCl2
Define the formation of covalent compounds
It involves sharing of electron pairs between one atom - generally non-metallic and another atom - also non-metallic. Electrons in the valence shell are mutually shared by the atom of each element such that each atom acquires a stable electronic configuration
Which atoms share 1 pair of electrons?
Non-metallic atoms having 7 [or 1] valence electrons
Which atoms share 2 pair of electrons?
Non-metallic atoms having 6 valence electrons
Which atoms share 3 pair of electrons?
Non-metallic atoms having 5 valence electrons
How do dissimilar non-metallic atoms form covalent molecules?
By sharing electron pairs
Define covalent bond
The chemical bond formed due to mutual sharing of electrons between the given pairs of atoms of non-metallic elements. Bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair
On what does the bond being single, double or triple covalent depend>
On the no. of electron pairs shared
Define covalent compound
It is the chemical compound formed due to mutual sharing of electrons between the given pairs of atoms thereby forming a covalent bond between them
Define covalency
The no. of electron pairs which an atom shares with one or more atoms of the same or different kind to achieve stable electronic configuration
When are covalent compounds said to be non-polar?
When shared pair of electrons are equally distributed between the two atoms
When are covalent compounds said to be polar?
When shared pair of electrons unequally distributed between the two atoms
Comment on the nature of the non-polar covalent molecule
No charge separation takes place. The covalent molecule is symmetrical and electrically neutral.
Comment on the nature of the polar covalent molecule
Charge separation takes place. The atom which attracts electrons more strongly develops a slight negative charge.
Give examples of non-polar covalent compounds
H2, Cl2, O2, N2, CH4, CCl4
Hydrogen, Chlorine, Oxygen, Nitrogen, Methane, Carbon tetrachloride
Give examples of polar covalent compounds
H2O, NH3, HCl
Water, Ammonia, Hydrochloric acid
How is a hydrogen molecule formed?
Each of the two ‘H’ atoms contributes one electron so as to have one shared pair of electrons between them. Both atoms attain stable - duplet structure, resulting in the formation of a single covalent bond [H-H] between them.
How is a chlorine molecule formed?
Each of the two ‘Cl’ atoms contributes one electron so as to have one shared pair of electrons between them. Both atoms attain stable octet structure, resulting in the formation of a single covalent bond [Cl-Cl] between them.
What is the nearest noble gas for oxygen?
Neon [2,8]
What is the nearest noble gas for hydrogen?
Helium [2]
What is the nearest noble gas for chlorine?
Argon [2,8,8]
How is an oxygen molecule formed?
Each of the two ‘O’ atoms contributes two electrons so as to have two shared pairs of electrons between them. Both atoms attain stable octet structure, resulting in the formation of a double covalent bond [O=O] between them.
How is a nitrogen molecule formed?
Each of the two ‘N’ atoms contributes three electrons so as to have three shared pairs of electrons between them. Both atoms attain stable octet structure, resulting in the formation of a triple covalent bond [N=N] between them.
How many electrons does carbon need to attain stable octet?
4 electron
Which is the nearest noble gas for carbon?
Neon [2,8]
Which is the nearest noble gas for chlorine?
Argon [2,8,8]
How many electrons does chlorine need to achieve stable octet?
One electron
How is carbon tetrachloride formed?
One atom of carbon shares four electron pairs - one with each of the four atoms of chlorine - four single covalent bonds
How does the formation of methane take place?
One atom of carbon shares four electron pairs - one with each of the four atoms of hydrogen - four single covalent bonds
How does the formation of water take place?
Each of the two hydrogen atoms shares an electron pair with the oxygen atom such that hydrogen acquires a duplet configuration and oxygen an octet configuration - resulting in the formation of - two single covalent bonds [H-O-H] in the molecule of water
How does the formation of ammonia take place?
One atom of nitrogen shares three electron pairs with each of the three atoms of hydrogen
What are lone pairs of electrons?
They are a pair of electrons that are not shared with any atom
Name a stable positive ion
Hydronium ion
Addition of acid to water results in release of which ion from the acid?
H+ ion
What is a coordinate bond?
Type of covalency which involves one of the combining atoms contributing both of the shared electrons i.e. a bond formed by a shared pair of electrons with both electrons coming from the same atom
Give another name for covalent bond
Dative or co-ionic bond
Name compounds containing electrovalent and covalent bond
NaOH, CaCO3
Name compounds containing coordinate and covalent bond
CO, HNO3
Name compounds containing electrovalent, covalent and coordinate bond
NH4Cl, K4 [Fe(CN)6] - Ferricyanide
What is form of the existence of ionic compounds?
Crystalline hard solids (at room temp.)
What is form of the existence of covalent compounds?
Gases, liquids or soft solids
Name the constituent units for ionic compounds
Ions (metallic, non-metallic)
Name the constituent units for covalent compounds
Molecules
How is the force of attraction in ionic compounds?
Strong
Where do electrostatic forces exist in ionic compounds?
Between ions
Why are ionic compounds hard solids?
Ions are closely packed with strong force of attraction, hence ionic compounds are hard solids
What is the volatility of ionic compounds?
Non-volatile
What is the mp and bp of ionic compounds?
They have a high melting and a high boiling point
Why do ionic compounds have high melting and boiling points?
Strong electrostatic force of attraction between ions. Large amount of energy required to break the force of attraction
Ionic compounds - conductors of heat
Good conductors of heat
In which state are ionic compounds good conductors of electricity?
Molten or aq. soln. state
Why are ionic compounds (soln.) good conductors of electricity?
Strong electrostatic force keeps ions in fixed position in the solid state. The force is weakened in the molten state and disappears in soln. state, hence free ions formed migrate to oppositely charged electrodes
Why are ionic compounds soluble in water but not in organic solvents?
Water (polar solvent) has a high dielectric constant, thus resulting in free ions. Organic solvents (non-polar) have low dielectric constants and do not cause dissolution
What is dielectric constant?
Capacity to weaken the force of attraction
What kind of reactions do ionic compounds undergo?
High speed ionic reactions
Why do ionic compounds undergo high speed ionic reactions?
Free ions formed in solution, rapidly regroup in solution
What happens to ionic compounds on passage of electric current?
Undergo electrolytic dissociation
What does the process of electrolytic dissociation involve for ionic compounds?
Separation of ions already present in the ionic compound
How is the force of attraction in covalent compounds?
Weak
Which forces exist between molecules in covalent compounds?
Vander Waal’s forces
Why are covalent compounds gaseous or liquid or soft solids?
Molecules have weak forces of attraction bet. them
What is the volatility of covalent compounds?
Volatile
What is the mp and bp of covalent compounds?
Low mp and low bp
Why do covalent compounds have low melting and boiling points?
Weak Vander Waals forces of attraction between molecules. Less amount of energy required to break this force of attraction
Covalent compounds - conductors of heat
Bad or non-conductors of heat
Why are covalent conductors non-conductors of heat in any state?
Non-polar covalent compounds contain molecules and not free ions, hence are non-conductors. Polar covalent compounds show charge separation and dissociate in H2O
In which state can covalent compounds undergo electrolysis?
In soln. state
Why are covalent compounds not soluble in organic solvents and not in water?
Organic solvents (non polar) dissolve non-polar covalent compounds (like dissolves like). Water cannot dissolve non-polar covalent compounds , but dissolves polar
What kind of reactions do covalent compounds undergo?
Slow speed molecular reactions
Why do covalent compounds undergo slow speed molecular reactions?
Covalent molecules are first broken and new bonds are slowly established
In which state do covalent compounds undergo ionisation?
In soln. state, on passage of electric current
What does ionisation of covalent compounds involve?
Formation of ions from molecules from molecules which are not in ionic state
