Module 2: Foundations in Chemistry

Question 1

Definition of Relative Isotopic Mass?

Answer 1

The mass of one atom of a particular isotope relative to the mass of 1/12th of a carbon-12 atom.

Question 2

How do you calculate Relative Atomic Mass?

Answer 2

You multiply the % Abundance by the mass number then add the abundance all together and divide by 100.

Question 3

Definition of a mole?

Answer 3

A mole is the amount of substances that contain as many particles as there are atoms in 12g of carbon-12.

Question 4

When working out Water of Crystallisation how do you find x?

Answer 4

You divide the moles of water by the moles of the salt.

Question 5

Percentage uncertainty formula?

Answer 5

(number of readings x max error/actual reading ) x100

Question 6

Volume of gas (cm3)

Answer 6

V =n x 24000

Question 7

Volume of gas (dm3)

Answer 7

V=n x 24

Question 8

What is the Limiting Reactant in a reaction?

Answer 8

The reactant that is used up first and stops the reaction.

Question 9

Ideal Gas Equation?

Answer 9

pV=nRT

Question 10

cm³ to m³

Answer 10

x10^-6

Question 11

dm³ to m³

Answer 11

x10^-3

Question 12

^oC to K

Answer 12

+273

Question 13

kPa to Pa

Answer 13

x10³

Question 14

What is a salt?

Answer 14

A salt forms when the H⁺ ion in an acid is replaced by a metal ion or NH₄⁺ ion.

Question 15

What is an orbital?

Answer 15

A region around the nucleus which can hold up to two electrons with opposite spins.

Question 16

What is First Ionisation Energy?

Answer 16

Energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous ions.

Question 17

First ionisation energy of X?

Answer 17

X_(g) –> X⁺_(g) + e^-

Question 18

Factors affecting Ionisation Energy?

Answer 18

• Atomic Radius
• Shielding
• Nuclear Charge

Question 19

Why does Ionisation Energy decrease as you go down a group?

Answer 19

As you go down a group:
* Atomic radius increases
* Shielding from electrons increases
* So despite an increase in nuclear charge
* less energy required to remove an electron

Question 20

Why does Ionisation Energy generally increase as you go across period?

Answer 20

As you go across a period:
* Nuclear charge increases
* Electrons are removed from the same shell with similar shielding
* Nuclear attraction increases
* Atomic radius decreases
* More energy is required to remove an electron.

Question 21

Why do Beryllium and Boron not follow the increase in Ionisation energy trend?

Answer 21

An electron is being removed from the 2p subshell in Boron and 2s in Beryllium, since it’s being removed from a higher energy subshell it is easier to remove.

Question 22

Why is Oxygen’s ionisation energy less than that of Nitrogen’s?

Answer 22

Paired electrons repel eachother, making it easier to remove an electron so it requires less energy to remove an electron from Oxygen.

Question 23

What is an ionic bond?

Answer 23

The electrostatic attraction between oppositely charged ions.

Question 24

If a molecule has 2 bonding pairs and 0 lone pairs shape and degrees?

Answer 24

Linear 180^o

Question 25

If a molecule has 3 bonding pairs and 0 lone pairs, shape and degrees?

Answer 25

Trigonal planar 120^o

Question 26

If a molecule has 4 bonding pairs and 0 lone pairs what is the shape and angle?

Answer 26

Tetrahedral 109.5^o

Question 27

If a molecule has 6 bonding pairs and 0 lone pairs what is the shape and degrees?

Answer 27

Octahedral 90^o

Question 28

If a molecule has 3 bonding pairs and 1 lone pair what is the shape and degrees?

Answer 28

Trigonal pyramedial 107^o

Question 29

If a molecule has 2 bonding pairs and 2 lone pairs what is the shape and degrees?

Answer 29

Non-linear 104.5^o

Question 30

Predict the bond angle in ammonia NH₃ molecule. 3 bond pairs and 1 lone pair

Answer 30

* Electrons repel eachother as much as possible. * Lone pairs repel more than bonded pairs. * NH₃ has 3 bond pairs and 1 lone pair. * Gives a bond angle of 107^o and Trigonal pyramedial shape.

Question 31

Definition of Electronegativity?

Answer 31

The tendency of a covalently bonded atom to draw the pair of bonding electrons towards itself.

Question 32

How do London forces exist?

Answer 32

* Fluctuations in electron density within a molecule or atom * Produce an instantaneous dipole moment * This induces a dipole moment in an adjacent atom * The two dipole moments create a weak temporary force of attraction.

Question 33

Why do larger molecules require more energy to break?

Answer 33

As molecular size increases the number of electrons increase, this makes London forces stronger as atomic or molecular mass increases.

Question 34

Why are Hydrogen bonds relatively strong?

Answer 34

N, O and F atoms are: * highly electronegative attracting electrons away from H atom * have at least a lone pair of electrons after bonding.

Question 35

Why is ice less dense than water?

Answer 35

In ice, water molecules are held apart from each other in a lattice occupying less space.

Question 36

Why does water have a relatively high surface tension?

Answer 36

Water molecules have a strong attraction for eachother.

Question 37

What is a metallic bond?

Answer 37

The electrostatic attraction between a metal cation and the delocalised sea of electrons.