The periodic table

Question 1

An element

Answer 1

is a substance that cannot be split into simpler substance by chemical means

Question 2

A triad

Answer 2

is a group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two.

Question 3

Newland’s octaves

Answer 3

are arrangements of elements in which the first and the eighth element, counting from a particular element, have similar properties.

Question 4

Limitation to Newland’s octaves

Answer 4

Did not account for undiscovered elements

Question 5

Mendeleev’s periodic law

Answer 5

when elements are arranged in order of increasing atomic weight, the properties of the elements recur periodically, i.e. the properties displayed by an element are repeated at regular intervals in other elements.

Question 6

The atomic number

Answer 6

of an atom is the number of protons in the nucleus of that atom

Question 7

Modern periodic table

Answer 7

When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically, i.e. the properties displayed by an element are repeated at regular intervals in other elements.

Question 8

Differences between Mendeleev’s periodic table and the modern periodic table

Answer 8

1. Mendeleev arranged elements in order of increasing atomic weight whereas the modern periodic table is arranged in order of increasing atomic number
2. Mendeleev’s table only included 60 elements whereas the modern periodic table has over 100
3. Mendeleev’s periodic table contains gaps for undiscovered elements, whereas the modern periodic table has no gaps
4. Mendeleev’s table did not have transition metals in a separate block, whereas the modern periodic table has transition metals in a separate block

Question 9

The mass number

Answer 9

of an element is the sum of the number of protons and neutrons in the nucleus of an atom of that element

Question 10

Isotopes

Answer 10

are atoms of the same element which have different mass numbers due to the different number of neutrons in the nucleus.

Question 11

Relative atomic mass

Answer 11

is defined as: the average of the mass numbers of the isotopes of the element, as they occur naturally, taking their abundances into account and expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units.

Question 12

Mass spectrometer

Answer 12

1. Used to measure relative atomic masses
2. Used to measure the percentage abundance of each isotope of an element

Question 13

The principle of mass spectrometry

Answer 13

is that charged particles moving in a magnetic field are deflected to different extent according to their masses and are thus separated according to these masses

Question 14

The five processes that occur in a mass spectrometer

Answer 14

1. Vaporisation
2. Ionisation
3. Acceleration
4. Separation
5. Detection

Question 15

Vaporisation

Answer 15

The sample is converted to a vapour

Question 16

Ionisation

Answer 16

An “electron gun” is used to knock electrons out of the atoms of the particles, converting them into positively charged ions.

Question 17

Acceleration

Answer 17

The ions are accelerated to high speeds by a series of negatively charged plates, with a narrow beam of the ions emerging through small holes in the plates

Question 18

Separation in a magnetic field

Answer 18

The beam of ions passes into a magnetic field, forcing the ions to be split into a number of beams depending on their masses.

Question 19

Detection

Answer 19

The strength of the magnetic field can be varied to bring the different beams into focus on a detector. The signal is amplified and passed onto a printer, producing a mass spectrum.

Question 20

Uses of the mass spectrometer

Answer 20

1. To identify the presence of isotopes
2. To measure the relative abundances of isotopes
3. To measure relative atomic masses and relative molecular masses.
4. To identify unknown compounds, e.g. detecting banned drugs taken by athletes, analysing trace organic pollutants in water and gases from waste dumps.

Question 21

Electron configurations of atoms

Answer 21

Describes the arrangement of electrons in the energy levels inside the atom.

Question 22

Formula for the number of electrons that a main energy level

Answer 22

2n squared
where n is the number of the energy level.

Question 23

Aufbau principle

Answer 23

When building up the electron configuration of an atom in its ground state, the electrons occupy the lowest available energy level.

Question 24

Hund’s rule of maximum multiplicity

Answer 24

states that when two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs.

Question 25

The Pauli exclusion principle

Answer 25

states that no more than two electrons may occupy an orbital and they must have opposite spins