Observations about the Periodic Table

Atomic Number

• Represents the number of protons in an atom's nucleus.
• Unique to each element; determines the chemical properties of the element.
• Example: The atomic number of Carbon (C) is 6, indicating it has 6 protons.

Atomic Mass

• Refers to the mass of an atom, typically expressed in atomic mass units (amu).
• Calculated as the weighted average of an element's isotopes.
• Example: The atomic mass of Carbon is approximately 12.01 amu due to its isotopes (C-12, C-13).

Valence Electrons

• Electrons in the outermost shell of an atom that determine its ability to bond with other atoms.
• Elements in the same group on the periodic table have the same number of valence electrons.
• Example: Sodium (Na) has 1 valence electron, while Chlorine (Cl) has 7.

Reactivity

• Describes how easily an element can react with other substances.
• Metals typically have high reactivity, especially alkali metals (e.g., Lithium, Sodium).
• Nonmetals also show reactivity; Halogens (e.g., Fluorine, Chlorine) are very reactive.

Metals vs Nonmetals

• Metals: Good conductors of heat and electricity, malleable, ductile, and typically shiny.
  • Located on the left side of the periodic table.
  • Example: Iron (Fe) and Copper (Cu).
• Nonmetals: Poor conductors, brittle (if solid), not ductile or malleable.
  • Located on the right side of the periodic table.
  • Example: Oxygen (O) and Nitrogen (N).

Metalloids

• Elements that have properties of both metals and nonmetals.
• Often used in semiconductors and alloys.
• Example: Silicon (Si) and Germanium (Ge).

States of Matter

• Elements can exist in different states: solid, liquid, or gas under standard conditions.
• Most metals are solids, while some nonmetals exist as gases (e.g., O2) or liquids (e.g., Br2).
• The physical state can affect an element's reactivity and bonding characteristics.