Foundations In Chemistry

Question 1

If an atom has 2 bonded electron pairs what is its bond angle and name?

Answer 1

Linear
180 degrees

Question 2

If an atom has 3 bonded electron pairs what is its bond angle and name?

Answer 2

Trigonal planar
120 degrees

Question 3

If an atom has 4 bonded electron pairs what is its bond angle and name?

Answer 3

Tetrahedral
109.5 degrees

Question 4

If an atom has 5 bonded electron pairs what is its bond angle and name?

Answer 4

Trigonal bipyrimidal
90 degrees and 120 degrees

Question 5

If an atom has 6 bonded electron pairs what is its bond angle and name?

Answer 5

Octahedral
90 degrees

Question 6

Define electronegativity

Answer 6

The tendency of a bonded atom to attract the electrons around it

Question 7

Define polar bond

Answer 7

When the bonded electron pair is unequally shared between the atoms

Question 8

What is a dipole

Answer 8

Partial charge resulted from the unequal sharing of electrons between molecules

Question 9

Define intermolecular forces

Answer 9

Weak interactions between dipoles of different molecules

Question 10

How does an induced dipole dipole form?

Answer 10

Fluctuation of electron density in molecule induces an instantaneous dipole which induces another dipole which results in a weak attraction

Question 11

Why do simpler molecules not readily dissolve in water ?

Answer 11

Little interaction between molecules in Lattice and the polar solvent molecules due to no polarity in covenant lattice

Question 12

Why do smaller/simpler molecules have lower melting/boiling points ?

Answer 12

•Usually have London forces which require less force to be broken
•less electrons results in smaller induced dipoles therefore easier to break

Question 13

What is an orbital ?

Answer 13

An area of probability of which two electrons with opposite spins can be found within a sub shell

Question 14

What is a dative bond

Answer 14

Shared pair of electrons supplied by one atom in a bond

Question 15

Define isoelectric

Answer 15

An Atom has same number of protons but different number of electrons

Question 16

Why is 4s sub shell filled before 3d?

Answer 16

4s is a lower energy level than 3d electrons fill lower energy levels first

Question 17

Why must electrons have opposite spin?

Answer 17

To counteract the repulsion between the two negative charges

Question 18

Why do ions dissolve in water ?

Answer 18

Water is an polar solvent. The dipole charges on the water are more favourable than the charges of the ions

Question 19

Define a covelant bond

Answer 19

Electrostatic forces between the nuclei and shared electron pair

Question 20

Define electron density

Answer 20

Probability of an electron being present with in a given area of an electron

Question 21

When does a covalent bond become an ionic bond ?

Answer 21

When the electronegativity difference is larger than 1.8 on the Pauling scale

Question 22

What happens to a covenant molecule when there is a lone pair of electrons in the outer shell?

Answer 22

Each lone electron pair will reduce bond angle by 2.5 degrees

Question 23

What two factors affect electronegativity

Answer 23

•atomic radius increase electronegativity decreases
•more unshielded protons higher electronegativity

Question 24

Define an acid

Answer 24

Compound that releases H+ ions in aqueous solution

Question 25

Define a base

Answer 25

Substance that accepts H+ ions from an acid

Question 26

Define an alkali

Answer 26

Releases OH- ions in aqueous solution

Question 27

Why are titrations used ?

Answer 27

To calculate the concentration of an acid of unknown concentration by neutralisation with a know concentration of an alkali

Question 28

Define oxidation number

Answer 28

Number of electrons lost shared or gained by an atom in a compound

Question 29

What are the exceptions for the oxidation numbers of hydrogen, oxygen and chlorine

Answer 29

Hydrogen — metal hydrides(-H)
Oxygen — peroxides (-1) and fluorine (+2)
Chlorine — compounds with Oxygen or Flourine

Question 30

Define oxidation and reduction in terms of oxidation number

Answer 30

Oxidation-Increase in oxidation number
Reduction-Decrease in oxidation number

Question 31

Define oxidising agent and reducing agent

Answer 31

•Oxidising agent: Oxidises something else resulting in reducing itself
•Reducing agent :Reduces something else resulting in oxidising itself

Question 32

Define disproportionation

Answer 32

Redox reaction in which same element is both oxidised and reduced