Isotopes are atoms of the same element which have different masses. They have the same number of protons, but different numbers of neutrons.

How it's Written

ZA SYMBOL

Inquiry Question 2:

Relative Atomic Mass (RAM)

The average mass of the isotopes of an element that occur naturally.

Example:

Lithium; RAM = 6.941amu

Isotope

(amu)

Relative Abundance

(%)

Lithium-6

6.015122

7.59

Lithium-7

7.016004

92.41

RAM Equation:

RAM = (% Abundance x AM)100 + (% Abundance x AM)100

Radioisotopes

Unstable Nuclei

The nucleus of an atom can become unstable because

The nucleus is too heavy (Z > 83)
The neutron: proton ratio is too high (too many neutrons)
The neutron: proton ratio is too low (too many protons)
The particles of the nucleus have too much energy

Alpha(α) Decay

The nucleus is too heavy
Alpha(α) particle is emitted
- 2 protons + 2 neutrons
  - Helium nucleus
- 24 He or24 α
- Charge of +2
Atom undergoes transmutation to form another element

Beta (β) Minus Decay

The neutron: proton ratio is too high (too many neutrons)
Beta (β) minus particle emitted
- An electron
- -10 e
- Charge of -1
Atom undergoes transmutation to form another element

Beta (β) Plus/ Positron Decay

The neutron: proton ratio is too low (too many protons)
Beta (β) plus particle emitted
- A positron
- +10 e
- Charge of +1
Atom undergoes transmutation to form another element

Gamma (γ) Decay

Excess energy is dissipated by the emission of gamma rays
Can occur with other types of nuclear decay
Gamma (γ) rays
- Electromagnetic radiation
- High energy
- High frequency
- Short wavelength

Types of Radioactive Decay

Type	Particle Consists of	Neutron to Proton Ratio	Formation: Description and Equation	A	Z	General Equation	Example
Alpha	2 protons + 2 neutrons (He nucleus)	Z > 83	Nucleus ejects an alpha particle (No equation for nuclear process)	-4	-2	^A_ZM → ^A-4_Z-2N +⁴₂He	²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
Beta	electron	High	Neutron transforms into a proton and an electron which is ejected from the nucleus. ¹₀n → ¹₁p + ⁰_-1e	same	+1	^A_ZM → ^A_Z+1N +⁰_-1e	¹⁴₆C → ¹⁴₇N + ⁰_-1e
Positron	positron (anti-electron)	Low	Proton transforms into a neutron and a positron which is ejected from the nucleus. ¹₁p → ¹₀n + ⁰₁e	same	-1	^A_ZM → ^A_Z-1N +⁰₁e	⁴⁰₁₉K → ⁴⁰₁₈Ar + ⁰₁e
Gamma	EMR	Nucleus Has Excess Energy	Nucleus releases excess energy as gamma rays (EMR) (No equation for nuclear process)	NA	NA	NA	^99m₄₃Tc → ⁹⁹₄₃Tc + γ

Nuclear stability

Green line: No. Neutrons = No. Protons

Red line: No. Neutrons against No. Protons of all stable nuclei/ Zone of stability

Zone of stability = 82, 124

Different Zones:

Any nuclei with Z>82 undergo alpha decay and are beyond the zone of stability

Nuclei with a neutron to proton ratio that is too high (too many neutrons) undergo beta minus decay emitting beta particles (electrons) and are above the zone of stability

Nuclei with a neutron to proton ratio that is too low (too many protons) undergo beta plus decay emitting positrons and are below the zone of stability

Penetration & Shielding

*Type of Radiation*	*Tissue Penetration (mm)*	*Shielding*
Alpha	0.045	Paper, Cloth
Beta	11.0	4mm Aluminium 1mm Lead
Gamma	130	40mm Lead 600mm Concrete

Ionising radiation

Alpha, beta and gamma radiation are ionising radiation
They cause atoms and molecules to become charged by removing or knocking out electrons
When atoms in a living cell becomes ionised:
- The cell dies
- The cell repairs itself
- The cell mutates and can become cancerous

Half-life

The time it takes for the concentration of a substance to fall to half of its initial value.
Alpha and beta emitters are very dangerous if they are ingested as they cannot penetrate the human tissue
Gamma emitters are easy to locate as they can be easily detected by a detector from the outside.

Bohr Model

Electrons are considered particles in this model

Moves in circular orbits
Each orbit has a certain energy
Enrgy of the orbit increases as the distance increases
Orbits = Shells/ energy levels

Absorbing Energy

Electrons absorb energy to move from a low energy to high energy
Energy must be absorbed as a packet or quantum that is exactly the required energy
Energy absorber = EMR (Electromagnetic Radiation)

Emitting Energy

Electrons emits energy to move from a higher energy to a lower one
EMR is emitted

Differences in Energy Levels

EMR is absorbed or emitted exactly the difference between levels
Energy of EMR determines colour

Bohr Model Absorption Emission Spectra Animated

Lowest Possible Energies

Electrons will always be located at the lowest possible energy level unless given extra energy
Called ground state

Schrödinger Model

Electrons are considered as waves in this model

3D Volumes

Position of an electron with a particular energy is a 3D volume where theres 99.9% chance of finding an electron
Named orbitals
> distance from the Nucleus = > energy of electrons & volume of orbital
Electrons moving is their orbitals move in an Electron cloud

Bohr vs Schrödinger

*Bohr*	*Schrödinger*
Electron = particle Circular or Orbits Energy increases as distance increases	Electron = Waves 3D or Volumes Energy increases as distance increases

Principal Energy Levels

Orbitals can only contain a max of 2 electrons

Sublevels (SPDF)

*Type of Sublevel*	*No. Orbitals*	*Max no. Electrons*
S	1	2
P	3	6
D	5	10
F	7	14

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰ … etc

Energy Level Diagram

Notation

Hund’s Rule

Long Hand

Full SPDF Notation = 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰ … etc

Short Hand

[Core Electrons/ First Noble Gas Before] Valence electrons

Inquiry Question 3

State at Room Temperature

*State*	*Melting Point*	*Boiling Point*
Solid	> 25°	> 25°
Liquid	< 25°	> 25°
Gas	< 25°	< 25°

Opposing Forces Within an Atom

*Attractive Force*	*Repulsion Force*
An attraction between the positively charged nucleus and the negatively charged electrons	A repulsion between the negatively charged electrons, particularly within the same level or sublevel

Shielding

The effective nuclear charge experienced by the outermost electrons decreases as the number of electrons between them and the nucleus increases.

As you go down a group, the shielding of an atom increases, but across a period it decreases

Atomic Radius

Atomic Radius: The distance from the center of the nucleus to the outermost electron

Atomic radius is determined by the force of attraction between the positive nucleus and the negative electrons, and by the force of repulsion between the negative electrons.
Across a period, the force of attraction increases because the No. of protons in the nucleus increases, but the outermost electrons move into the same energy level
The rate at which the attractive force increases is much greater than that of the repulsive force between the electrons.

Down a group, the atomic radius increases

From group I to VII, across the period, the atomic radius decreases

From group VII to VIII, across the period, the atomic radius increases

First Ionisation Energy

The energy required to remove the most loosely held electrons from a natural gaseous
The stronger the force of attraction between the positive nucleus & negative electrons, the greater the first ionization energy

Across the period, the first ionization energy increases

Down a group, the first ionization energy decreases

Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons
The electronegativity of an atom is a relative measurement and is give as a number between 0 and 4
Atoms with a small atomic radius and less shielding will have a higher electronegativity because the force of attraction experienced by the outermost electrons will be greater

Across a period, electronegativity increases