Module 2 – Foundations in chemistry

Question 1

What are isotopes?

Answer 1

Atoms of the same element with the same numbers of protons (and electrons) but different numbers of neutrons and different masses.

Question 2

What is the atomic number?

Answer 2

The number of protons in an atom.

Question 3

What is the mass number?

Answer 3

The total number / sum of the neutrons and protons in the nucleus of an atom.

Question 4

What are ions?

Answer 4

Atoms of the same element with the same numbers of protons (and neutrons) but different numbers of electrons and different charges.

Question 5

What is the relative mass of an electron?

Answer 5

1/1836 or negligible

Question 6

What is the actual charge on a single proton/ electron?

Answer 6

1.60 × 10^-19 C

Question 7

What is the standard mass/unit for atomic mass?

Answer 7

1u

Question 8

Where does 1u come from?

Answer 8

1/12 the mass of a carbon-12 atom

Question 9

What is the relation of 1u to protons and neutrons?

Answer 9

1u = ~ the mass of a proton or neutron

Question 10

What is relative isotopic mass?

Answer 10

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

Question 11

What is relative atomic mass (Ar)?

Answer 11

The weighted mean mass of an atom of an element relative to 1/ 12th the mass of a carbon-12 atom.

Question 12

What is the equation for relative atomic mass?

Answer 12

[Sum of (Relative abundance × mass)] ÷ total relative abundance

Question 13

What are the basic principles of mass spectroscopy?

Answer 13

1. Sample is placed in mass spectrometer
2. Sample is vaporised, then ionised to form positive ions.
3. Ions are accelerated so they have the same kinetic energy
   • the heavier the ion the longer it takes to reach the detector, the lighter the shorter it takes
4. Ions are detected as a mass to charge ratio (m/z)
   • each ion produces a signal - the greater the signal the greater the abundance

Question 14

What is the equation for mass to charge ratio?

Answer 14

Mass to charge ratio (m/z) = relative mass of ion ÷ relative charge on ion

Question 15

How do you calculate the relative atomic mass from m/z?

Answer 15

Relative atomic mass = [sum of (m/z × abundance)] ÷ total abundance

Question 16

What is relative molecular mass?

Answer 16

Mr is the relative mass of chemicals with a fixed formula in terms of the number of atoms involved.

Question 17

What is the relative formula mass?

Answer 17

It is the relative mass of chemicals using an empirical formula to represent them e.g. compounds with giant structures.

Question 18

What are principle quantum shells labelled with?

Answer 18

Principle quantum numbers (n)

Question 19

What is the formula for the maximum number of electrons in a shell n?

Answer 19

2n^2

Question 20

What is the formula for the maximum number of electrons in a shell n?

Answer 20

2n^2

Question 21

What is an atomic orbital?

Answer 21

Regions of space around a nucleus where electrons are most likely found holding up to 2 electrons with opposite spins.

Question 22

What are the 4 sub-shells in order of energy?

Answer 22

S-, p-, d- and f- sub-shells.

Question 23

What is the shape of s- and p- orbitals?

Answer 23

Sphere and dumbell respectively.

Question 24

The greater the shell number, …

Answer 24

The greater the size of the shell and the distance from the radius.

Question 25

Which shells contain s-orbitals and how many?

Answer 25

All shells from n=1, 1 s-orbital.

Question 26

How many p-orbitals are there, what are they, and where are they relative to each other?

Answer 26

3; Px, Py and Pz; perpendicular.

Question 27

Which shells contain p-orbitals and how many?

Answer 27

From n=2, 3 p-orbitals.

Question 28

Which shells contain d-orbitals and how many?

Answer 28

From n=3, 5 d-orbitals.

Question 29

Which shells contain f-orbitals and how many?

Answer 29

From n=4, 7 f-orbitals.

Question 30

What is the order if shell filling from 1s to 4f?

Answer 30

1s 2s 2p 3s 3p 4s 3d 4p 4d 4f

Question 31

What is the order of emptying from 4f to 1s?

Answer 31

4f 4d 4p 4s 3d 3p 3s 2p 2s 1s

Question 32

What is Krypton's electron number and electron configuration?

Answer 32

36; 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^6

Question 33

What is ionic bonding?

Answer 33

The electrostatic force of attraction between positive and negative ions.

Question 34

What are cations and anions?

Answer 34

Positive and negative ions respectively.

Question 35

What does the empirical formula show?

Answer 35

The ratio of different ions in a molecule.

Question 36

What are the physical properties of ionic substances? (4)

Answer 36

High melting/ boiling points: high amounts of energy required to break strong ionic bonds. Most are soluble in polar substances: the polarised molecules attract to the oppositely charged ions. Electrical conductivity when aqueous or molten: the ions are free to move and carry electrical charge throughout the structure in these states. Brittle: distorting layers mean like charges repel and the lattice breaks.

Question 37

What is covalent bonding?

Answer 37

The strong electrostatic force of attraction between a shared pair of electrons and the nuclei of bonded atoms.

Question 38

What is orbital theory?

Answer 38

When orbitals overlap, a region of space is formed where an electron pair can be found; new molecular orbitals are formed.

Question 39

Why is covalent different to ionic bonding?

Answer 39

Covalent: localised attraction, non-metals, shared electrons. Ionic: attraction in all directions, non-metals and metals, transferred electrons.

Question 40

What are lone pairs?

Answer 40

Unshared paired electrons.

Question 41

Which elements exist diatomically?

Answer 41

H, N, Cl, Br, O, I

Question 42

How many bonds does Boron form covalently?

Answer 42

3 (6 rather than 8 electrons in outershell)

Question 43

Which 3 elements from period 3 do not follow noble gas configuration?

Answer 43

Phosphorus, sulfur, and fluorine.

Question 44

What is dative covalent (coordinate) bonding?

Answer 44

Covalent bonding in which the shared pair of electrons has been supplied by one of the bonding atoms only.

Question 45

What is bond energy and its units?

Answer 45

The energy required to break one mole of a particular covalent bond in the gaseous states; unit = kJmol^-1.

Question 46

What is bond length?

Answer 46

The internuclear distance between two covalently bonded atoms.

Question 47

How does bond energy and bond length affect the strength of the covalent bond?

Answer 47

The greater the bond length, the smaller the bond energy, and the weaker the covalent bond.

Question 48

What is the order of single, double, and triple bonds in length and strength of covalent bonds?

Answer 48

Shortest and strongest to longest and weakest: triple, double, single.

Question 49

What is average bond enthalpy?

Answer 49

It is used as the measurement of the strength of a covalent bond and is the average amount of energy required to break a specific type of bond, measured over a wide variety of different molecules.

Question 50

The greater the average bond enthalpy...

Answer 50

The stronger the covalent bond.