Reactivity & Structure 1: Models Of The Particulate Nature Of Matter

Question 1

Democritus’ Model

Answer 1

Theorized that matter could be continually split until a size where it could not be split any further. He called these tiny pieces atomos, meaning “indestructible” in Greek.

Question 2

Dalton’s Model

Answer 2

All matter is made up of atoms, which are tiny, indivisible particles. All the atoms of an element have the same size, mass, and properties but the atoms of different elements have different sizes and masses. Atoms cannot be created, destroyed, or divided into smaller particles.

Question 3

J. J. Thompson’s Model

Answer 3

The Plum Pudding Model, in which electrons were embedded in a sphere of positive charge.

Question 4

The Cathode Ray Experiment

Answer 4

J. J. Thompson’s experiment showed that all atoms contain tiny negatively charged subatomic particles or electrons.

He placed two oppositely-charged plates around the cathode ray, and the ray was deflected from the negative plate but attracted to the positive one.

Question 5

Rutherford’s Model

Answer 5

Described the atom as having a tiny, dense, and positively charged core called the nucleus. It was established that the mass of the atom was concentrated in its nucleus. The light, negatively charged, electrons circulated around this nucleus. It was the first dynamic/planetary model.

Question 6

The Gold Foil Experiment

Answer 6

Rutherford fired a beam of alpha particles at a thin sheet of gold that was surrounded by a censor that would flash when hit. It was predicted that the particles would pass straight through, as the Plum Pudding Model stated that the positive charges were spread out and subsequently too weak to impact the particles. However, some particles were deflected, resulting in the conclusion that the positive charge must be localized over a very tiny volume of the atom and that the atom must be made up of mostly empty space.

Question 7

Bohr’s Model

Answer 7

Electrons can only exist in stationary orbits around the nucleus, which are associated with discrete energy levels that converge at higher energy.

Question 8

Emission Line Spectrum

Answer 8

Produced by hot gas. Shows the release of a photon of a specific energy as electrons return to a lower level, related to a specific frequency of light.

Question 9

Absorption Line Spectrum

Answer 9

Produced by cold gas, shows the absorption of a photon of specific energy as they are excited to a higher level, related to a specific frequency of light.

Question 10

The Electromagnetic Spectrum

Answer 10

*Left to right

Gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves.

(Raging Martians Invaded Venus Using X-ray Guns)

Question 11

Allotropes

Answer 11

Alternative forms of an elemental substance. For example, diamond and graphite are allotropes of carbon.

Question 12

The Kinetic Molecular Theory

Answer 12

1. All matter is made up of particles/molecules/atoms
2. All particles have kinetic energy that causes them to constantly move
3. No intermolecular forces
4. Completely elastic collisions, no loss in kinetic energy
5. The amount of energy is proportional to the temperature

Question 13

Density

Answer 13

The density of a substance is its mass per unit volume (mass ÷ volume). Substances with higher densities will feel ‘heavier’ compared to substances with lower densities (of the same volume).

d = m ÷ v

Question 14

Sublimation

Answer 14

Solid to gas with no liquid state. Heat is absorbed.

Question 15

Deposition

Answer 15

Gas to solid with no liquid state. Heat is released.

Question 16

The Atomic Number

Answer 16

The atomic number (symbol Z) is the number of protons in the nucleus of an atom.

Question 17

The Mass Number (Nucleon Number)

Answer 17

The mass number (symbol A), also called the nucleon number , is the number of protons and the number of neutrons in the nucleus of an atom.

Question 18

Relative Atomic Mass

Answer 18

The weighted average mass of an atom compared to 1/12 the mass of an atom of carbon-12.

Can be calculated by multiplying the percent abundance with the masses of the isotopes then dividing by 100.

[(Percent abundance • mass of isotope) ÷ 100]

Question 19

Mass Spectrometer

Answer 19

An instrument that is used to determine the abundance of the various isotopes of an element, based on a measurement of the mass-to-charge (m/z) ratio of ions within a sample of the element.

Question 20

Five Stages of a Mass Spectrometer

Answer 20

1. Vaporization: substance is vaporised to produce gaseous molecules.
2. Ionization: high-energy electrons are fired at gaseous molecules, causing them to be ionised, forming gaseous ions (known as molecular ions).
3. Acceleration: the gaseous ions are accelerated in an electric field.
4. Deflection: the gaseous ions are deflected by an electromagnet. The degree of deflection they undergo depends on their m/z ratio. Ions with lower m/z ratios are deflected the most and ions with higher m/z ratios are deflected the least.
5. Detection: the gaseous ions are detected and a mass spectrum is produced.

Question 21

Emission Spectra

Answer 21

The range of frequencies or wavelengths of electromagnetic radiation emitted during an electron transition from a higher to a lower energy level.

Question 22

Principal Quantum Number

Answer 22

The main energy levels occupied by electrons, assigned the letter “n”.

Question 23

Degenerate Orbitals

Answer 23

Atomic orbitals that have equal energy levels. For example, the three 3p orbitals are degenerate orbitals.

Question 24

Aufbau Principle

Answer 24

States that when adding electrons to an atom, the lower energy orbitals must be filled first.

Question 25

Pauli Exclusion Principle

Answer 25

States that an atomic orbital can only hold two electrons and they must have opposite spins.

Question 26

Hund’s Rule

Answer 26

States that when we have degenerate orbitals (orbitals of the same energy) then each orbital is filled with a single electron before being doubly occupied.

Question 27

First Ionization Energy

Answer 27

The energy required with remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 28

First Ionization Energy: Beryllium and Boron

Answer 28

First ionization energy decreases from beryllium to boron because:

beryllium: 1s² 2s²
boron: 1s² 2s² 2p¹

Electrons in p orbitals are of higher energy and further from the nucleus than electrons in s orbitals, therefore they require less energy to remove.

Question 29

First Ionization Energy: Nitrogen and Oxygen

Answer 29

First ionization energy decreases from beryllium to boron because:

nitrogen has the electron configuration 1s² 2s² 2p³
oxygen has the electron configuration 1s² 2s² 2p⁴

An electron in a doubly occupied orbital is repelled by the second electron and requires less energy to remove than an electron in a half-filled orbital.

Question 30

Exothermic Reactions

Answer 30

Describes a reaction in which energy is transferred or released to the surroundings.

Question 31

Endothermic Reactions

Answer 31

Describes a reaction in which energy is transferred or absorbed from the surroundings.

Question 32

Enthalpy

Answer 32

Measurement of heat energy within a system. It is symbolised in expressions by H.

Question 33

Standard Enthalpy Change

Answer 33

The heat energy transferred within a reaction under standard conditions with all substances present in their standard states.

Question 34

Specific Heat Capacity

Answer 34

The quantity of energy needed to raise 1 g of a substance by 1 K.

Question 35

Change in Enthalpy

Answer 35

ΔH (change in enthalpy) = -Q (thermal energy) ÷ n (number of moles)

Question 36

Bond Enthalpy

Answer 36

The energy required to break one mole of chemical bonds in the gaseous state.

• Bond enthalpy values are always positive because they refer to bonds being broken (bond breaking is endothermic).