Study Notes on Atomic Structure, Stability, and Bonding

Mass number of an atom indicates the total number of protons and neutrons.
- Example: For Hydrogen, the mass number is approximately 1.008, which rounds to 1.
The atomic number refers specifically to the number of protons in the atom.
To find the number of neutrons, use the formula: $\text{Neutrons} = \text{Mass Number} - \text{Atomic Number}$
- For hydrogen:
- Atomic number = 1 (protons)
- Mass number = 1 (protons + neutrons)
- Neutrons = $1 - 1 = 0$
Importance of protons, neutrons, and electrons in understanding atomic stability and reactivity.

Electrons determine whether an atom is stable or reactive.
- Stable: Does not bond with other elements.
- Reactive: Seeks to bond with other elements to attain stability, often leading to the formation of molecules.

Atomic number: 6
- Protons: 6
- Electrons: 6
- Neutrons: 12 - 6 = 6
Electron configuration:
- First energy level: 2 electrons
- Second energy level: 4 electrons
Valence electrons: 4
Reactive because it needs 4 more electrons to reach stability, can bond with hydrogens to form methane.

Atomic number: 7
- Protons: 7
- Electrons: 7
- Neutrons: 14 - 7 = 7
Electron configuration:
- First energy level: 2 electrons
- Second energy level: 5 electrons
Valence electrons: 5
Reactive, needs 3 more electrons to be stable.

Atomic number: 8
- Protons: 8
- Electrons: 8
- Neutrons: 16 - 8 = 8
Electron configuration:
- First energy level: 2 electrons
- Second energy level: 6 electrons
Valence electrons: 6
Highly reactive; seeks 2 more electrons to complete its octet.

First Energy Level holds a maximum of 2 electrons.
Second Energy Level holds a maximum of 8 electrons.
Octet Rule: For stability, atoms prefer to have either 2 or 8 electrons in their outermost energy level.
Valence electrons determine reactivity. Elements react to achieve a full valence shell.

Noble gases have full valence shells.
- Examples: Helium (2 electrons), Neon (10 electrons).
These gases are stable and do not tend to bond with other elements because they already have full electron shells.

Major elements by body weight percentage:
1. Oxygen
2. Carbon
3. Hydrogen
4. Nitrogen
Other important elements: Calcium, Phosphorus are also significant.
Minor elements play crucial roles as electrolytes, which are ions that can conduct electricity - important for muscular and nervous functions (e.g., sodium, potassium, calcium).

Isotopes: Atoms of the same element with different numbers of neutrons, resulting in different mass numbers.
- Example: Carbon-12 (6 protons, 6 neutrons) vs. Carbon-13 (6 protons, 7 neutrons) vs. Carbon-14 (6 protons, 8 neutrons).
- Radioactive isotopes can emit radiation due to instability, which is utilized in medical applications.

Molecule: Two or more atoms bonded together, can be of the same or different elements.
Compound: Two or more different elements bonded together.
- Example: $H<em>2$ (molecule) vs. $H</em>2O$ (both molecule and compound).

Involve the transfer of electrons.
- Ions: Charged particles that result from electrons being gained or lost.
- Cation: Positively charged ion (e.g., sodium loses an electron).
- Anion: Negatively charged ion (e.g., chlorine gains an electron).
- Example: Sodium (Na) and Chlorine (Cl) form sodium chloride (NaCl) through ionic bonding.

Involve sharing electrons between atoms to achieve stability.
Covalent bonds form between nonmetal atoms.
Example: The bond in molecules like methane (CH₄), where carbon shares its valence electrons with hydrogen.

Atoms and their interactions through electrons play a fundamental role in forming the molecules that constitute all matter, particularly biological matter. Understanding atomic structure, stability, and bonding principles is essential for studying chemistry and biology at the cellular level.