Atoms, Molecules, and Chemical Bonds

Atoms, Molecules, and Chemical Bonds

• Atoms are the fundamental building blocks of matter, like oxygen (O₂), water (H₂O), or glucose (C₆H₁₂O₆).

• Atoms consist of three subatomic particles: protons (+ charge), neutrons (no charge), and electrons (- charge)

• The nucleus contains protons and neutrons; electrons orbit the nucleus.

• The atom's nucleus accounts for almost all of its mass.

• Protons are equal to the number of electrons in a neutral atom.

• Unstable atoms have more neutrons than protons; they are radioactive.

• The atomic number (Z) is a unique number equal to the number of protons.

• The atomic mass (A) is the sum of protons and neutrons.

• Atoms can gain or lose electrons, forming ions with a positive (+ cation) or negative (- anion) charge.

• Electrons occupy energy levels (shells) and sublevels (s, p, d, f) that contain orbitals.

• Orbitals represent high probability regions of finding electrons.

• There are maximum numbers of electrons allowed in each level/sublevel/orbital.

Elements

• Elements are substances made of one type of atom.

• Elements are organized according to their atomic number in the periodic table.

• Elements on the periodic table are listed in increasing order of atomic number.

• Atomic number (number of protons in the nucleus) determines an element's properties and identity.

• The periodic table is organized by increasing atomic number, grouping elements with similar chemical properties in columns.

• The first ten elements make up 99.8% of the Earth's crust (oxygen, silicon, aluminum, etc.).

Molecules and Chemical Bonds

• Molecules are formed when atoms combine through chemical bonding.

• Two common types of chemical bonds are covalent and noncovalent bonds (ionic and others).

• Covalent bonds form when atoms share pairs of electrons to achieve a stable electron configuration (often following the octet rule).

• Covalent bonds are strong and common in biological molecules.

• Polar covalent bonds involve unequal sharing of electrons, creating partial charges on the atoms.

• Nonpolar covalent bonds involve equal sharing of electrons, resulting in no partial charges.

• Examples of covalent bonds include single, double, and triple bonds.