Chemistry · Unit 3 · Quick reference
Periodic Table
Grades 9–12+2 pages
All 118 elements with atomic number, symbol, name, standard atomic weight and common ion charges; families, trends, ions, filling order and constants.
1The Periodic Table of the Elementsperiods across, groups down; color = the sublevel being filled
2Reading the Table
- Period
- a row; the period number is the outer energy level (n) being filled
- Group
- a column (1–18); same group, same outer-electron pattern, similar chemistry
- Block
- s, p, d or f: the sublevel that receives the last electron
- Valence e⁻
- outer s + p electrons; groups 1–2 have 1–2, groups 13–18 have 3–8 (He: 2)
Metals, nonmetals, metalloids
- Metals (left and center): shiny, conduct, lose electrons to form cations.
- Nonmetals (upper right, plus H): gain or share electrons; many are gases.
- Metalloids (heavy outline) sit on the border and behave in between; Si and Ge are semiconductors.
| Group | Family | Valence e⁻ | Typical ion |
|---|---|---|---|
| 1 | alkali metals (not H) | 1 | 1+ |
| 2 | alkaline earth metals | 2 | 2+ |
| 3–12 | transition metals | varies | often 2+ or 3+ |
| 15 | nitrogen family | 5 | 3− |
| 16 | chalcogens (oxygen family) | 6 | 2− |
| 17 | halogens | 7 | 1− |
| 18 | noble gases | 8 (He 2) | none |
Rank by ionization energy Worked
Na, Mg, Cl, Ar (period 3)
Na < Mg < Cl < Arleft to right
| Property | Across a period → | Down a group ↓ |
|---|---|---|
| atomic radius | decreases | increases |
| ionization energy | increases | decreases |
| electronegativity | increases (F highest) | decreases |
| metallic character | decreases | increases |
Why
- Across: more protons, same shell → stronger pull, smaller atom.
- Down: one more shell each period → electrons farther out, easier to remove.
- Dips in ionization energy: B < Be (new p sublevel), O < N (first paired p electron).
Seven elements travel in pairs
H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂: start at element 7 (N), trace the shape of a 7 through O, F, Cl, Br, I, then add H. (Traditional picture.)
Fluorine is the corner bully
The pull rises toward the upper right, so F (3.98) has the greatest electronegativity; noble gases are left out of the scale.
3Ions, Electrons & Constants
| Ion | Name | Ion | Name |
|---|---|---|---|
| NH₄⁺ | ammonium | OH⁻ | hydroxide |
| NO₃⁻ | nitrate | NO₂⁻ | nitrite |
| SO₄²⁻ | sulfate | SO₃²⁻ | sulfite |
| PO₄³⁻ | phosphate | CO₃²⁻ | carbonate |
| HCO₃⁻ | hydrogen carbonate | C₂H₃O₂⁻ | acetate |
| ClO₃⁻ | chlorate | ClO₄⁻ | perchlorate |
| MnO₄⁻ | permanganate | CN⁻ | cyanide |
| CrO₄²⁻ | chromate | Cr₂O₇²⁻ | dichromate |
| O₂²⁻ | peroxide | Hg₂²⁺ | mercury(I) |
Naming metal ions
- One common charge (groups 1–2, Al, Zn, Ag): just the element name: Na⁺ sodium ion.
- Several charges: Roman numeral = charge: Fe²⁺ iron(II), Fe³⁺ iron(III), Cu⁺ copper(I).
- Anions end in -ide: Cl⁻ chloride, O²⁻ oxide, N³⁻ nitride.
-ate has more O than -ite
Nitrate NO₃⁻ vs nitrite NO₂⁻: “ate ate one more oxygen.” Same charge, one fewer O for -ite.
Electron configurations Worked
Fe (26): [Ar] 4s² 3d⁶
Fe³⁺: [Ar] 3d⁵lose 4s first
Cr: [Ar] 4s¹ 3d⁵; Cu: [Ar] 4s¹ 3d¹⁰half or full d
- Avogadro
- N_A = 6.02214076 × 10²³ mol⁻¹ (exact)
- Gas constant
- R = 0.08206 L·atm/(mol·K) = 8.314 J/(mol·K)
- Molar volume
- 22.41 L/mol at 0 °C, 1 atm
- Pressure
- 1 atm = 760 mmHg = 101.325 kPa
- Water
- c = 4.184 J/(g·°C); K_w = 1.0 × 10⁻¹⁴ at 25 °C
- Light
- c = 2.998 × 10⁸ m/s; h = 6.626 × 10⁻³⁴ J·s
About the numbers
Atomic weights: IUPAC CIAAW abridged standard atomic weights (2024 revision). Elements with no stable isotopes show a bracketed mass number (from PubChem, NIH). Names use U.S. spelling (aluminum, cesium).