Molecules, Atoms, and Ions

• Molecules consist of two or more atoms bonded, forming the smallest unit of a substance.
• Atomic number equals the number of protons in the nucleus of an atom.
• Protons are positively charged particles within an atom.
• A cation is a positively charged ion.
• An anion is a negatively charged ion.
• Group number indicates the number of electrons in the outermost shell of an atom.
• Period number indicates the number of electron shells an atom has.
• Neutrons are uncharged particles found in the nucleus of an atom.
• Mass number is the total count of protons and neutrons in an atom.
• Electron configuration is a notation describing how electrons are arranged within an atom's shells.
• Valence electrons are the electrons located in the outermost shell of an atom.
• Components/subatomic diagrams show the arrangement of protons, neutrons, and electrons within an atom.
• Atoms have no overall charge because they contain an equal number of positively charged protons and negatively charged electrons.
• Isotopes are atoms having the same number of protons but differing numbers of neutrons.
• Lattice structure refers to the 3D arrangement of atoms in groups.
• Ground state is when the diagram/electrons stay the same, while the excited state is when the electrons jump to the outer shells.
• The number of neutrons can be found by subtracting the atomic number from the mass number.
• The number of protons is the same as the atomic number.
• Elements can be represented by their symbol, atomic number, element name, and mass number.
• For ions with a positive charge, it is the atomic number minus the charge number.
• For negative it is the atomic number plus the charge number.
• Ions only exist when an atom is charged (positive or negative).
• Protons remain constant for each element in any chemical reaction.
• Atoms are most stable with 8 electrons in their outer shell and gain or lose electrons to achieve this.
• An atom that is positively or negatively charged is called an ion, of which there are two types: cations and anions.
• Elements with 1, 2, or 3 electrons in their outer shell tend to lose electrons and become cations.
• Metals tend to lose electrons.
• Elements with 5, 6, or 7 electrons in their outer shell tend to gain electrons and become anions.
• Non-metals tend to gain electrons.
• The periodic table position helps predict an ion's charge.

Atomic Model Development

• Dalton's model proposed indivisible spheres.
• Thomson's model introduced the "plum pudding" model with embedded electrons.
• Rutherford discovered the nucleus.
• Bohr's model introduced quantized electron orbits.