4 chemical bonding and structure

Question 1

4.1 what is an ion?

Answer 1

an ion is a charged particle. it forms from atoms or groups of atoms when they lose or gain one or more electrons

Question 2

why do chemicals bond?

Answer 2

to achieve stability

Question 3

definition of cations

Answer 3

atoms that lose electrons to form a noble gas electron configuration and have a positive net charge

Question 4

definition of anions

Answer 4

atoms that gain electrons to form a noble gas electron configuration and have a negative net charge

Question 5

what is an ionic bond

Answer 5

electrostatic attraction experienced between the electric charges of a cation and anion

Question 6

what is a lattice?

Answer 6

structures that consists of three dimensional repeating units of positive and negative ions

Question 7

state that transition metals

Answer 7

can form more than one ion

Question 8

conditions for ionic bond

Answer 8

no of valence electrons
between a metal and non metal
between atoms with low and high electronegativity
exothermic reaction
big diff in electronegativity

Question 9

what determines ionic character

Answer 9

1. position of elements in the periodic table
2. electronegativity

Question 10

electronegativity of ionic compounds

Answer 10

electronegativity difference of about 1.8 is the point where a bond may be thought of as ionic, there are a few exceptions to this rule such as HF, in which the electronegativity difference is 1.9, but the molecular properties are decidedly covalent

Question 11

what is lattice enthalpy?

Answer 11

strength of force between ions

Question 12

what is the magnitude of lattice enthalpy affected by?

Answer 12

higher the charge and smaller the size of ions; larger the lattice enthalpy and more energetically stable the compound

Question 13

volatility of ionic compounds

Answer 13

volatility is the tendency of a substance to vaporise

for ionic compounds the electrostatic forces of attraction are strong hence volatility is low

Question 14

electrical conductivity of electrical compounds

Answer 14

electrons are not free to move in solid state however they are free to move in molten state and able to conduct electricity

Question 15

solubility of ionic compounds

Answer 15

dissolve in polar solvents such as water since partial charges on water are attracted to ions in the lattice

Question 16

4.2 what is covalent bond?

Answer 16

a covalent bond is formed by the electrostatic attraction between a shared pair of electrons and positively charged nuclei

Question 17

what are lone pairs?

Answer 17

lone pairs are non bonding pairs of electrons

Question 18

types of covalent bonds

Answer 18

single covalent bond (1 pair of e shared)
double covalent bond (2 pair of e shared)
triple covalent bond (3 pair of e shared)

Question 19

what is a dative/coordinate covalent bond?

Answer 19

formed when both electrons of the shared
pair of electrons originate from the same
atom

Question 20

symbol of a coordinate covalent bond

Answer 20

an arrow on the head of the bond is used to indicate the origin of the electron pair

Question 21

what is a polar covalent bond?

Answer 21

covalent bond in which electrons are shared unequally
- due to unequal electronegativity
- thus bonded atoms acquire a partial positive/negative charge

Question 22

trend in bond strength

Answer 22

triple bond > double bond > single bond

Question 23

trend in bond length

Answer 23

single bond > double bond > triple bond

Question 24

properties of covalent bonds

Answer 24

formed between non metals
covalent compounds consist of molecules
low mp and bp
may be volatile
typically insoluble in water
do not conduct electricity since there are no ions to carry charge

Question 25

4.3 what is the octet rule?

Answer 25

atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons

Question 26

exceptions on the octet rule

Answer 26

second-row elements B and Be often have
fewer than eight electrons around them in their
compounds (e deficient molecules)

second-row elements never exceed
the octet rule, since their valence orbitals
(2s and 2p) can accommodate only eight
electrons

third-row and heavier elements often
satisfy the octet rule but can exceed the
octet rule by using their empty valence d
orbitals (expand octet)

Question 27

properties of electron deficient molecules

Answer 27

molecules with incomplete octets, which tend to accept an electron pair from a molecule with a lone pair

Question 28

explanation of the order of electron repulsion among lone pair and bonding pair

Answer 28

electron repulsion trend
LP – LP > LP – BP > BP – BP

1. orbitals that hold lone pairs are rounder and shorter and spread more easily
2. orbitals that hold bonding pair are more elongated

Question 29

definition of lewis structure

Answer 29

a diagram of molecules in which the valence e of the atom are represented by dots, and the sharing of e to form a covalent bond is shown

Question 30

steps to draw a lewis structure

Answer 30

step 1
a. put the less electronegative atom at the center
b. use only “—” single bond to link the central atom to all the surrounding atoms
c. use only “..” lone pairs to complete the octet of each surrounding atom

step 2
a. calculate total no. of valence e used so far
b. calculate the total no. of valence e from all atoms
c. calculate difference, put the extra electrons as “x x”
lone pair or “x” single unpaired electron on
the central atom

step 3
a. calculate the Formal Charge (F.C.) for each atom
Formal Charge = valency – no. of electrons assigned to the atom
b. use the lone pairs on the surrounding atoms to make “=” or “≡” bonds to lower the Formal Charge on each atom as close to zero as possible

Question 31

comment of formal charge

Answer 31

if a nonzero Formal Charges are present;
make sure the positive formal charge is on the less electronegative atom and the negative formal charge is on the more electronegative atom

Question 32

VSPER theory

Answer 32

Valence Shell Electron Pair Repulsion Theory

total number of electron domains determines the shape of a covalent molecule

1. repulsion applies to both bonding and non-bonding pairs (lone pairs) of electrons
2. the total number of electron domain around the central
   atom determines the electron domain geometry
3. lone pairs have a higher concentration of charge than a
   bonding pair because they are not shared between two
   atoms and so they cause more repulsion than bonding
   pairs

Question 33

difference between electron domain geometry and molecular geometry

Answer 33

The electron domain geometry is determined by the positions of all the electron domains

Molecular geometry (arrangement of atoms in space) depends on the positions of the bonded atoms