Atomic Structure, Radioactive Decay, and Chemical Bonds Explained
Atomic Nucleus and the Strong Force
Protons and neutrons bind together to form the nucleus of an atom. Negatively charged electrons are attracted to the positively charged protons and orbit the nucleus. The strong force, also known as the strong interaction, color force, or strong nuclear force, holds protons and neutrons together. This force is more powerful than the electrical repulsion between protons, but it requires the particles to be in close proximity.
Ions: Atoms with a Charge
An ion is an atom or molecule with a net electric charge due to an imbalance in the number of electrons and protons. This occurs when an atom loses or gains one or more electrons.
Fundamental Forces and Their Mediators
- Gravity: graviton – infinite range
- Electromagnetic: photon – infinite range
- Strong: gluons – short range
- Weak: vector boson – short range
Radioactive Decay and Half-Life
A radioisotope has a half-life of 4 hours. If you start with 10g:
- After 4 hours: 5g
- After 8 hours: 2.5g
- After 16 hours: 1.25g
Types of Radioactive Decay
Five kinds of radioactive decay and their effect on the number of protons and neutrons in the nucleus:
Three major types of nuclear decay:
- Alpha emission: -2 protons, -2 neutrons (Helium nucleus)
- Beta emission: neutron converts to proton, emitting an electron
- Gamma emission: 0 change in protons or neutrons (emission of a high-energy photon)
- Electron Capture and Positron Emission: change in neutron number: +1
Penetration Power of Radiation
- Alpha particles can be stopped by cardboard.
- Beta particles can be stopped by aluminum.
- Gamma particles can be stopped by lead.
Chemical Bonds: Strength and Types
The three main types of chemical bonds, from strongest to weakest:
Covalent Bond
Involves the sharing of electrons between two atoms. The shared electrons form a new orbit around the nuclei of both atoms, creating a molecule.
Ionic Bonding
Involves the transfer of an electron from one atom to another. One atom gains an electron (anion, negative charge), and the other loses an electron (cation, positive charge). The opposite charges attract, bonding the atoms together.
Dative Covalent Bond
A covalent bond where both electrons in the shared pair come from one atom. This occurs when a nucleophile (electron-rich species with a lone pair) donates to an electrophile (electron-deficient species).
Half-Life Example
If you have 20g of a substance with a half-life of 6 hours:
- After 6 hours: 10g
- After 12 hours: 5g
Sound and Hearing
The softest sound a human can hear is around 20 Hz… 0 dB.
Immediate Hearing Loss
An example of a sound that can cause immediate hearing loss is a jet engine, which produces sound levels around 120 dB.
Resonance and Frequency
A thick string vibrates with a lower frequency (pitch) than a thin string. The selectivity or preference of a string for a certain range of frequencies is called resonance. The frequency at which it vibrates when plucked is its resonant or natural frequency.