Chemistry Basics: Atoms, Molecules, and Compounds

Counting Atoms and Molecules

• A molecule is formed when two or more atoms bond together

Isotopes

• Isotopes are atoms of an element with the same number of protons (atomic number) but differing numbers of neutrons, resulting in different atomic masses
• Neutrons can be calculated by subtracting the atomic number from the atomic mass

Ionic Compounds

• Ionic compounds are formed from the combination of ions (charged particles) with opposite charges
• Metals lose electrons to form cations, while non-metals gain electrons to form anions
• Ionic compounds are named with the metal followed by the non-metal with an "ide" ending

Molecular Compounds

• Molecular compounds are formed when two or more different elements bond together
• Example: Water (H2O) is a molecular compound

Molecular Bonds

• Covalent bonds form when two non-metal atoms share electrons to form a molecule
• The nucleus of one atom is attracted to the valence electrons of another atom, leading to electron sharing and bond formation

Noble Gases

• Noble gases are a family of elements in the 18th column of the periodic table
• They are stable and unreactive due to their full outer shell

Reactivity of Metals

• Metals closer to the edges of the periodic table are more reactive
• In the left side of the periodic table, higher periods indicate more reactivity
• In the right side of the periodic table, lower periods indicate more reactivity

Physical Properties of the Periodic Table

• Metals are typically found on the left side of the periodic table and have properties such as being shiny, malleable, and conductive
• Non-metals are typically found on the right side of the periodic table and have properties such as being dull, brittle, and insulating
• Metalloids are found on the border of the staircase and exhibit intermediate properties

Metals

• Metals are typically solid at room temperature
• They are shiny and malleable, and can conduct heat and electricity

Non-metals

• Non-metals can exist in solid, liquid, or gas states at room temperature
• They are dull, brittle, and insulating

Boiling Points

• Boiling points increase from left to right across a period due to increasing metallic bond strength
• Boiling points decrease for groups 1, 2, and 18 as you move down the periodic table
• Boiling points increase for group 17 as you move down the periodic table

Patterns of the Periodic Table

• Charges (family): +1, +2, (varies for 3-12), +3, +/-4, -3, -2, -1, 0
• Bonding capacity (family): 1, 2, (varies for 3-12), 3, 4, 3, 2, 1, 0
• Valence electrons (family): 1, 2, (varies for 3-12), 3, 4, 5, 6, 7, full
• Shells: increase by period, with period 1 having 1 shell, period 5 having 5 shells, etc.

Families

• Family 1: Alkali Metals
• Family 2: Alkaline Earth Metals
• Family 17: Halogens
• Family 18: Noble Gases

Subatomic Particles

• Atoms consist of protons and electrons, with protons never changing for an element
• Protons and electrons are equal in number for an atom

Bohr-Rutherford Diagram

• The first shell can hold up to 2 electrons
• The second and third shells can hold up to 8 electrons
• The nucleus consists of protons and neutrons