Basic Concepts Of Chemistry ( Includes Chemical Nomenclature, Atomic Structure, Periodic Table, Chemical Bonding And Molecular Structure, Stoichiometry, Chemical Equilibrium & Acids-Base Chemistry)

Front 1

What is chemical bond?

Back 1

A force that acts between two or more atoms to hold them together as a stable molecule.

Hint 1

Attractive force

Front 2

How was the term valency derived?

Back 2

The term valency was derived from the Latin word 'valentia' which means capacity.

Hint 2

Valentia

Front 3

Why does chemical combination happens?

Back 3

i) Decrease in energy (becoming stable

ii) to attain octet configuration

Hint 3

Low energy and attaining that magic number

Front 4

What is electronic theory of valency?

Back 4

Two or more atoms in a bond try to attain a noble configuration

Front 5

What is formal charge?

Back 5

(No. of valence electrons in the free atom) - (no. of unshared electrons on the atom (while in the bond)) - (no. of bonds around the atom)

Hint 5

Charge on a single atom in a bond

Front 6

Limitations of the octet rule

Back 6

1)the incomplete octet of the central atom

2)odd-electron molecules

3)the expanded octet

4)does not account for the shape of molecules

5)relative stability of the energy of the molecule is not explained

Hint 6

Examples: BCl3, NO2, H2SO4

Many noble gases also form molecules like KrF2, XeOF2 etc

Front 7

What is an electrovalent bond?

Back 7

Just another name for ionic bond.

Front 8

What is a dative bond?

Back 8

A covalent bond in which both electrons of the shared pair are contributed by one of the two atoms.

It is represented by A - -> B.

Front 9

What is electronegativity difference?

Back 9

The difference between the electronegativity of two elements in a bond

Front 10

How much (minimum) electronegativity is necessary for an ionic bond to occur?

Back 10

About 2

Front 11

What is lattice energy ⚡?

Back 11

Energy released to form one mole of a crystal lattice of a compound is called lattice energy.

Front 12

What is a Crystal lattice?

Back 12

Hint 12

The symmetrical 3d arrangement of atoms inside a crystal

Front 13

General properties of ionic compounds

Back 13

-hard and possess high melting and boiling points

-dissolves in polar solvents

-doesn't exhibit isomerism

-in aqueous solutions or in fused state, they act as conductors.

Hint 13

💪 💦

Front 14

What is a Bond length?

Back 14

The distance between the nuclei of two atoms bonded together is termed bond length or bond distance.

Front 15

How is a Bond length calculated?

Back 15

Spectroscopically (or) by x-ray diffraction of solids and electron diffraction of gases.

Hint 15

Radius of 1st element + radius of 2nd element

Front 16

Is the bond length of C-C bond (single bond) and C=C (double bond) equal?

Back 16

No, its actually decreases as the number of bonds (single double or triple) increases.

Front 17

What is a bond angle?

Back 17

Angle between two adjacent bonds of an atom in a molecule made up of three or more atoms is known as the bond angle.

Front 18

What is bond energy (bond enthalpy)?

Back 18

Amount of energy required to break a bond (usually one mole) in a molecule.

Front 19

What is H-H bond enthalpy in hydrogen molecule?

Back 19

H(g) + H(g) - > 2H(g)

It's bond energy is (delta)H = 436 KJ mol^-1

Hint 19

Bond energy

Front 20

What does strength of bond depend on?

Back 20

1) bond length (shorter the length, greater is the strength)

2) bond order (single or multiple bonds)

3)no. of atoms in a molecule (monoatomic or polyatomic)

Also remember that bond energy changes for an atom in different molecules or compounds.

Hint 20

Bond length, order and the # of atoms in a molecule

Front 21

How does the no. of bonds (single or multiple bonds) affect the strength of bond?

Back 21

Triple bond>double bond>single bond between the same atoms of diatomic molecules

Front 22

What does a larger bond dissociation enthalpy means?

Back 22

It means that larger the bond energy, stronger will be the bond in the molecule.

Hint 22

Dissociation = (chemistry) the splitting of a molecule into smaller molecules, atoms or ions, especially by a reversible process.

Front 23

How is the bond enthalpy measured in case of polyatomic molecules like, H2O?

Back 23

H2O(g) - > H(g) + OH(g) ;

Here (delta)H = 502 KJ mol^-1 &

OH(g) - > H(g) + OH(g) ;

Here (delta)H = 427 KJ mol^-1

Now we take the avg of the two bonds broken = (502 + 427)/2 = 464.5 KJ mol^-1

Hint 23

H2O 💦

H-O-H (it has two bonds to be broken)

Front 24

Why is mean or average bond enthalpy used?

Back 24

It is used in the case of polyatomic molecules (like H2O). It is done as:

H2O 💦 H-O-H (it has two bonds to be broken) if you break a bond you will get OH(g) and H(g).

Now for the second bond you need to break the OH(g) molecule which requires less energy than H(g) and OH(g).

# Now you just need to divide the total bond dissociation enthalpy by the number of bonds broken.

You can also break the O atom first which would yield 2H(g) + O(g); (delta)H = 926 kj mol^-1

Hint 24

To find the bond energy required to break a single bond in a polyatomic molecule.

Front 25

What is bond order?

Back 25

No. of bonds (or) number of shared electron pairs between two atoms in a molecule

Hint 25

# of bonds

Front 26

Isoelectronic molecules (or) ions and bond order?

Back 26

They have same bond order.

Front 27

What is the role of resonance in the changing of bond order?

Back 27

Resonance changes the bond order.

Bond order = total no. of bonds between two atoms all the structures/total no. of resonating structures

Front 28

What is resonance?

Back 28

Whenever a single Lewis structure cannot describe a given molecule accurately (doesn't agree with the experimental results), a no. of structures can be written for a molecule (those structures are correct according to the Lewis structure rules but aren't accurate), then the actual structure is said to be a resonance hybrid or mesomeric hybrid of all these alternative structures.

Hint 28

A hybrid variety (which is the really real one) of all the possible structures that can be drawn for it.

Front 29

What is a canonical form (in resonance structures)?

Back 29

The various structures of which the molecule is a resonance hybrid are known as canonical or mesomeric forms.

Hint 29

Pseudo structures of the hybrid (true) molecule

Front 30

How are the canonical structures denoted?

Back 30

The are denoted by the symbol <----> between them.

Hint 30

What is the symbol?

Front 31

Difference between the energy of resonance hybrid and canonical forms of a single atom?

Back 31

Energy of resonance hybrid is less than that of any single canonical structures

Front 32

What is polarity of covalent bond?

Back 32

In reality no bond of compound is either completely covalent or ionic in nature.

Hint 32

Polar = directly opposite in character or tendency.

Front 33

What are non-polar bonds?

Back 33

When the shared electron pairs are equally attracted by the two atoms and therefore spend same amounts of time near each nucleus makes the molecule neutral or non-polar.

Hint 33

Eg:H2, O2, Cl2, F2 etc (homonuclear diatomic molecules)

Front 34

What are polar (covalent) bonds?

Back 34

In case of heteronuclear atoms, the shared pairs of electrons shifts more towards the atom with more electronegativity. Due to this the molecules gets two (partial or sometimes full (in case of ions)) oppositely charged poles, and the bond is said to be a polar covalent bond.

Hint 34

Eg:HF, HCl, HBr, HI, CsCl etc (heteronuclear diatomic nuclear)

Front 35

What is dipole moment?

Back 35

The polarity of a molecule is indicated in terms of dipole moment (μ).

μ = electric charge × bond length (distance between the charges)

μ = q × d

Hint 35

μ = q × d

Front 36

How is dipole moment measured?

Back 36

μ = q × d

Dipole moment is measured in 'Debye' units (D), where

1 D = 3.33 x 10^-30 coulomb metre

Further dipole moment is a vector quantity and is depicted by the symbol +---> (shown in the above picture). + sign on positive end and arrow head on negative end.

Hint 36

Debye

Front 37

Calculation of dipole moment of molecules with more than two atoms.

Back 37

-As dipole moment is a vector quantity it's resultant will be equal to all the bond dipoles (individual dipole moments of bonds) added.

-normal vector addition can be used (think or triangle law or parallelogram law of vector addition)

Hint 37

Vector addition

Front 38

What are symmetrical molecules?

Back 38

CO2, BF3, CH4, CCl4 are symmetrical and have zero resultant dipole moment. They are symmetrical because their central atom doesn't contains lone pair of electrons in addition to the bond pairs.

They are non-polar even though it contains polar bonds, as the symmetrical bonds cancel each other out

Front 39

What are unsymmetrical polyatomic molecules?

Back 39

H2O, CH3Cl, NH3, etc are unsymmetrical non-linear polyatomic molecules. As their central atom has lone pairs in addition to bond pairs,it causes distortion in the geometry of the molecule.

Front 40

What are fajan's rules?

Back 40

-For a given cation, covalent character increases with increase in size of the anion

-For a given anion, covalent character increases with decrease in size of the cation

-Covalent character increases with increasing charge either on cation or on anion

-Covalent character is high for compounds with cations with pseudo noble gas electronic configuration (18 electrons in the valence shell) compared to compounds with cations with noble gas electronic configuration (8 electrons in the valence shell)

Hint 40

Just as all covalent bonds have some partial ionic character, the ionic bond also have partial covalent character.

Front 41

What is VSEPR theory?

Back 41

Valence Shell Electron-Pair Repulsion theory. It predicts the shapes of molecules

Hint 41

Prediction of shapes

Front 42

What is vsepr theory based on?

Back 42

It is based on the repulsive interactions of the electron pairs (bonded or non-bonded) in the valence shell of the atoms

- It suggests that these electron pairs tend to occupy such positions in space that minimize repulsion and thus maximize separation between them.

Hint 42

Repulsive interactions of the electron pairs

Front 43

What is the order of repulsive interaction of electron pairs (between lone pairs and bond pairs)

Back 43

Lone pair = lp; Bond pair = bp

lp - lp > lp - bp > bp - bp

Front 44

Why does lone pair electrons occupy more space as compared to bond pair electrons?

Back 44

While the lone pair electrons are localized on the central atom, each bond pair electrons are shared between the two atoms. This leads to the lone pairs occupying more space than bond pair electrons.

Hint 44

Bond pairs are shared

Front 45

How to apply VSEPR method?

Back 45

Draw a Lewis structure of the molecule or ion.

-note down the number of electron groups around the central atom

(Note 📝 : a double and a triple bond each is counted as as one electron group)

-identify the election group geometry and molecular geometry (from the above table)

Electron group geometry is just the geometrical shape without any lone pairs i.e.,the first one of every group in the above table (they are linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral)

Hint 45

Need to memorize the molecular geometry table.

Front 46

Why was valence bond theory (or) molecular orbital theory developed?

Back 46

The Lewis or octet concept doesn't explain:

-the cause of covalent bond formation

-nature of the forces acting between them

-why different amounts of energy is released during the formation of different molecules

-shape of the molecules

-why the molecules are stable even though there are less than or more than 8 electrons in the valence shell

& the vsepr theory only explains the shapes of the molecules.

So to explain the above limitations the valence bond theory and molecular orbital theory based on quantum mechanics have been proposed.

Hint 46

As lewis, octet and vsepr theories have limitations

Front 47

What are the forces that arises when two atoms approach each other?

Back 47

°Attractive forces between

1)the nucleus of one atom and its own electron(s)

2)the nucleus of one atom and the electron(s) of other atom

&

°Repulsive forces between 1)electrons of both the atoms 2)nuclei of both the atoms.

If the magnitude of newly formed attractive forces are more than repulsive forces, they bond.

Hint 47

Front 48

What happens to the the potential energy of two atoms approaching each other?

Back 48

The potential energy steadily decreases as they comes closer. Ultimately a stage is reached where the net force of attraction balances the force of repulsion and system acquires minimum energy. At this stage the atoms are said to be bonded together to form a stable molecule.

(Note:The graph is to be studied from left to right & the energy which is released when the bond is formed is given by the minimum in the curve)

Hint 48

Decreases

Front 49

Difference between Sigma(σ) and pi bonds(π)?

Back 49