Introduction to Atoms and Elements

Historically, humans have observed that the environment is composed of various substances, each possessing distinct properties.
These properties include:
- Light reflection: Ways in which a substance reflects or fails to reflect light.
- Color: The specific visual hue of a substance.
- States of matter: The condition of a substance at a specific temperature, appearing as a solid, liquid, or gas.
Substances also demonstrate specific behaviors when reacting with each other under certain circumstances.
Examples of substances cited include:
- Carbon: Shown specifically in its graphite form.
- Lead: Identified as a metallic solid substance.
- Gold: Identified as a metallic solid substance.
Matter changes states depending on temperature and chemical reactions:
- Gold or lead can become liquid if the temperature is raised high enough.
- Carbon can be transformed into a gaseous state by burning it, which breaks its structure and releases it into the atmosphere.
Observation of air particles reveals different types, such as carbon, oxygen, or nitrogen, each having different properties.

Elements are defined as pure substances that possess specific properties at certain temperatures and react in specific ways.
Common examples of elements include carbon, lead, and gold.
Historical misconceptions labeled water as an element, but modern science identifies water as a compound made of more basic elements: oxygen and hydrogen.
The Periodic Table of Elements is the organizational chart for all known elements. Relevant elements mentioned include:
- Carbon (symbol: $C$ )
- Oxygen (symbol: $O$ )
- Nitrogen (symbol: $N$ )
- Silicon (symbol: $Si$ )
- Gold (symbol: $Au$ )
- Lead (symbol: $Pb$ )

The atom is the most basic unit of any element.
If a chunk of an element (such as carbon, gold, or lead) is broken into smaller and smaller pieces, the smallest unit that still retains the properties of that element is the atom.
Breaking an atom down further results in the loss of the properties associated with that specific element.
Scale of the Atom: Atoms are unimaginably small.
Example (Human Hair):
- The average human hair is composed primarily of carbon ( $C$ ).
- If you were to look at a cross-section of a human hair (the width, not the length), you could string approximately $1,000,000$ carbon atoms across it.
- This scale is intended to illustrate that an individual atom is nearly impossible to visualize because it is so minute.

Atoms are composed of even more fundamental building blocks. The arrangement of these particles defines the element and its properties.
The three primary subatomic particles are:
- The Proton: This is the defining particle of an element. The number of protons in an atom's nucleus determines which element it is.
- The Neutron: Part of the nucleus that is neutral in charge; its number can vary within atoms of the same element.
- The Electron: Negatively charged particles that surround the nucleus.
Atomic Number: The atomic number of an element is equal to the number of protons in its nucleus. In the periodic table, elements are listed in order of their atomic number.
Examples of Atomic Numbers:
- Hydrogen: $1$ proton (Atomic Number $1$ ).
- Helium: $2$ protons (Atomic Number $2$ ).
- Carbon: $6$ protons (Atomic Number $6$ ).
- Nitrogen: $7$ protons (Atomic Number $7$ ).
- Oxygen: $8$ protons (Atomic Number $8$ ).
- Fluorine: $9$ protons (Atomic Number $9$ ).
If the number of protons in an atom changes, the element itself changes (e.g., adding a proton to oxygen makes it fluorine).

The Nucleus: Located at the center of the atom, it contains both protons and neutrons.
Nuance in Neutrons: While the number of protons is fixed for an element, the number of neutrons can change, creating different versions of the same element.
Examples of Carbon Isotopes:
- Carbon-12: A version of carbon that contains $6$ protons and $6$ neutrons. The " $12$ " represents the total sum of protons and neutrons in the nucleus.
- Carbon-14: A version of carbon that still contains $6$ protons (as required by its identity as carbon) but contains $8$ neutrons.
The nucleus is where the vast majority of the atom's mass is concentrated.

Charge: Protons have a positive charge, and electrons have a negative charge.
Electromagnetic Force: Unlike charges attract each other. This attractive force between the positive nucleus and the negative electrons is what keeps the electrons bound to the atom instead of flying off.
Neutrality: An atom is considered neutral if it has an equal number of protons and electrons, resulting in the charges canceling each other out (e.g., carbon with $6$ protons and $6$ electrons).
Electron Positioning: Electrons do not orbit the nucleus in a fixed path like planets around a sun. Instead, they "buzz" or "jump" around the nucleus at extremely high velocities.
High velocity prevents the electrons from simply falling into the nucleus despite the attractive force.
To truly understand electron behavior, one must study quantum physics, as reality becomes very strange at the subatomic level.

Chemistry is largely the study of how electrons interact between different atoms.
Atoms can gain, lose, or share electrons based on their configuration and their affinity for electrons.
Ions and Net Charge:
- If a neutral carbon atom (with $6$ protons and $6$ electrons) loses an electron to another atom, it then has $5$ electrons and $6$ protons.
- This results in a net positive charge ( $+1$ ).
The way electrons are configured determines how an atom will bond, attract, or repel other atoms of the same or different elements.