chem 1

Element: Fundamental chemical substance that cannot be decomposed by normal chemical means.
Classification: Elements classified as Metals and Non-metals.

Definition: Tabular array of chemical elements organized by atomic number (protons in nucleus).
Structure: 18 Groups (columns) and about 7 Periods (rows).

Atomic Number: Indicates number of protons.
Groups: Represent valence electrons and similar chemical properties.
- Group 1 (IA): Alkali metals (1 valence electron).
- Group 2 (IIA): Alkaline Earth metals.
- Group 16 (VIA): Oxygen Family.
- Group 17 (VIIA): Halogens.

Electron Configuration: Arrangement of electrons in atomic orbitals.
Electron Affinity: Ability of an atom to gain an electron; implies energy change.
Electronegativity: Tendency of an atom to attract shared electrons in a bond; increases left to right, decreases top to bottom.
Electropositivity: Tendency of an atom to donate electrons; increases top to bottom in groups.
Ionization Energy: Energy required to remove an electron from an atom; increases left to right in a period, decreases top to bottom.
Atomic Radius: Distance from nucleus to valence shell; increases down a group, decreases left to right.

Arrangement of metals by reactivity; more reactive metals are easier to oxidize.
Useful for predicting displacement reactions.

Standard notation for electron distribution among orbitals; can be abbreviated using noble gases.
Example: Sodium - $1s^2 2s^2 2p^6 3s^1$ or abbreviated as $[Ne] 3s^1$.

Aufbau Principle: Electrons fill lower energy orbitals first.
Pauli Exclusion Principle: Maximum of two electrons per orbital; must have opposite spins.
Hund’s Rule: Each orbital in a subshell gets one electron before pairing to maximize total spin.