Chemistry Chapter 2: Atomic Structure

Study Notes

Understanding chemistry is fundamental to biology; interactions among atoms are the basis of biological organization.
Key elements in life include oxygen (O), nitrogen (N), carbon (C), and hydrogen (H), which together constitute about 96% of living matter.
Essential elements also include potassium (K), sulfur (S), phosphorus (P), calcium (Ca), sodium (Na), chlorine (Cl), and magnesium (Mg), while trace elements are present in minute amounts (3.7%).

Atoms consist of three main subatomic particles:
- Protons (positively charged)
- Neutrons (neutral)
- Electrons (negatively charged)
One Dalton (the unit of atomic mass) is equivalent to 1.67 x 10^-24 grams.
Atomic number indicates the number of protons; atomic mass (or mass number) is the sum of protons and neutrons.

Electron orbitals represent the regions around the nucleus where electrons are likely to be found.
Electron shells are layers around the nucleus that can hold electrons with specific energy levels.
Valence electrons are those in the outermost shell, which play a critical role in chemical bonding.

Ions are charged atoms that result from the loss or gain of electrons; ionization refers to this process.
Anions are negatively charged ions (gained electrons), while cations are positively charged ions (lost electrons).
Isotopes are variants of elements that have the same number of protons but different numbers of neutrons; radioisotopes are unstable isotopes that decay over time.

Atoms tend to react and form chemical bonds to achieve a filled valence shell.
Chemical bonds may form compounds or molecules, defined by their molecular formulas or structural formulas.
Electronegativity measures an atom's ability to attract electrons; significant differences in electronegativity between two atoms lead to electron transfer and bond formation.

Ionic bonds occur when one atom (with lower electronegativity) transfers an electron to another atom (with higher electronegativity), resulting in charged ions.
This transfer influences the stability and reactivity of atoms, playing a crucial role in the formation of compounds.