Chemistry: Periodic Table Element Groups & Trends Cheatsheet

Introduction to the Periodic Table

The periodic table is a systematic arrangement of chemical elements organized by increasing atomic number and recurring chemical properties. Created by Dmitri Mendeleev in 1869 and refined by later scientists, the modern periodic table contains 118 confirmed elements arranged in 7 periods (rows) and 18 groups (columns). This arrangement reveals patterns and trends that help predict physical and chemical behaviors of elements, making it one of the most powerful tools in chemistry.

Structure of the Periodic Table

Basic Organization

• Periods: Horizontal rows (numbered 1-7)
• Groups: Vertical columns (numbered 1-18 in modern convention)
• Blocks: s-block, p-block, d-block, and f-block (based on the electron subshell being filled)

Major Regions

• Metals: Left and center of the table (~80% of elements)
• Nonmetals: Upper right section
• Metalloids: Diagonal border between metals and nonmetals
• Main Group Elements: Groups 1, 2, and 13-18 (s-block and p-block)
• Transition Elements: Groups 3-12 (d-block)
• Inner Transition Elements: Lanthanides and Actinides (f-block)

Element Groups and Their Properties

Group 1: Alkali Metals

Elements: Li, Na, K, Rb, Cs, Fr Properties:

• Soft, silvery, highly reactive metals
• Single valence electron (ns¹)
• Low ionization energies
• Strong reducing agents
• React vigorously with water to produce H₂ gas and metal hydroxides
• Form ionic compounds with 1+ charge
• Stored under oil to prevent reaction with air
• Increase in reactivity down the group

Key Compounds:

• Sodium chloride (NaCl): table salt
• Sodium hydroxide (NaOH): lye, soap production
• Potassium nitrate (KNO₃): fertilizer, gunpowder
• Lithium carbonate (Li₂CO₃): treatment for bipolar disorder

Group 2: Alkaline Earth Metals

Elements: Be, Mg, Ca, Sr, Ba, Ra Properties:

• Harder and denser than alkali metals
• Two valence electrons (ns²)
• Low (but higher than Group 1) ionization energies
• Strong reducing agents (less than Group 1)
• React with water (less vigorously than Group 1)
• Form ionic compounds with 2+ charge
• Increase in reactivity down the group

Key Compounds:

• Calcium carbonate (CaCO₃): limestone, chalk, marble
• Magnesium oxide (MgO): refractory material
• Calcium sulfate (CaSO₄): plaster, gypsum
• Barium sulfate (BaSO₄): contrast agent for X-rays

Groups 3-12: Transition Metals

Properties:

• Metallic, good conductors of heat and electricity
• Variable oxidation states
• Form colored compounds
• Many are catalytically active
• Often form complex ions
• Generally hard and have high melting points
• Less reactive than Groups 1 & 2

Notable Elements:

• Iron (Fe): Structural material, hemoglobin component
• Copper (Cu): Electrical wiring, excellent conductor
• Zinc (Zn): Galvanization, enzyme component
• Silver (Ag): Photography, highest electrical conductivity
• Gold (Au): Resistant to corrosion, jewelry, electronics
• Titanium (Ti): Lightweight, strong, corrosion-resistant
• Platinum (Pt): Catalytic converters, jewelry
• Mercury (Hg): Liquid at room temperature

Group 13: Boron Group

Elements: B, Al, Ga, In, Tl Properties:

• Three valence electrons (ns²np¹)
• Boron is a metalloid; others are metals
• Form compounds with +3 oxidation state
• Aluminum is the most abundant metal in Earth’s crust

Key Compounds:

• Aluminum oxide (Al₂O₃): abrasive, component of gemstones
• Borax (Na₂B₄O₇·10H₂O): cleaning agent, buffer
• Aluminum sulfate (Al₂(SO₄)₃): water purification

Group 14: Carbon Group

Elements: C, Si, Ge, Sn, Pb Properties:

• Four valence electrons (ns²np²)
• Carbon is a nonmetal; silicon and germanium are metalloids; tin and lead are metals
• Can form four covalent bonds
• Show +2 and +4 oxidation states
• Transition from nonmetallic to metallic properties down the group

Key Compounds:

• Carbon dioxide (CO₂): greenhouse gas, carbonated beverages
• Silicon dioxide (SiO₂): glass, sand, quartz
• Tin(IV) oxide (SnO₂): tin plating, ceramic glazes
• Lead(II) oxide (PbO): batteries, glass production

Group 15: Nitrogen Group (Pnictogens)

Elements: N, P, As, Sb, Bi Properties:

• Five valence electrons (ns²np³)
• Nitrogen is a gas; phosphorus is a solid with multiple allotropes; arsenic and antimony are metalloids; bismuth is a metal
• Form compounds with -3, +3, and +5 oxidation states
• Transition from nonmetallic to metallic properties down the group

Key Compounds:

• Ammonia (NH₃): fertilizer production, cleaning agent
• Nitric acid (HNO₃): manufacturing explosives, fertilizers
• Phosphoric acid (H₃PO₄): fertilizers, food additive
• Phosphates: detergents, fertilizers, ATP in biological systems

Group 16: Oxygen Group (Chalcogens)

Elements: O, S, Se, Te, Po Properties:

• Six valence electrons (ns²np⁴)
• Oxygen and sulfur are nonmetals; selenium and tellurium are metalloids; polonium is a metal
• Form compounds with -2 oxidation state
• Oxygen is highly electronegative; forms oxides with most elements
• Sulfur has multiple allotropes

Key Compounds:

• Water (H₂O): universal solvent, crucial for life
• Hydrogen peroxide (H₂O₂): bleaching agent, disinfectant
• Sulfuric acid (H₂SO₄): industrial chemical, battery acid
• Metal sulfides: ores for metal extraction

Group 17: Halogens

Elements: F, Cl, Br, I, At Properties:

• Seven valence electrons (ns²np⁵)
• All are nonmetals (except possibly astatine)
• Highly reactive, form -1 ions (halides)
• Exist as diatomic molecules (X₂)
• Strong oxidizing agents (decreasing down the group)
• React with metals to form salts
• Decrease in electronegativity down the group
• Increase in atomic radius down the group

Key Compounds:

• Sodium chloride (NaCl): table salt
• Hydrochloric acid (HCl): stomach acid, industrial chemical
• Chlorine (Cl₂): water purification
• Iodine: essential for thyroid function
• Fluorides: dental health

Group 18: Noble Gases

Elements: He, Ne, Ar, Kr, Xe, Rn Properties:

• Complete valence shell (ns²np⁶, except He: 1s²)
• Extremely stable, mostly unreactive
• Exist as monatomic gases
• Low boiling points
• Used in lighting, cryogenics, and inert atmospheres

Key Compounds:

• Xenon forms compounds with fluorine and oxygen
• XeF₂, XeF₄, XeO₃ – rare examples of noble gas compounds

Lanthanides and Actinides

Lanthanides (First Row of Inner Transition Elements)

Elements: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu Properties:

• Called “rare earth elements” (though not all are rare)
• Filling of 4f orbitals
• Similar chemical properties
• Most common +3 oxidation state
• Decrease in atomic radius across the series (lanthanide contraction)
• Used in magnets, catalysts, and phosphors

Actinides (Second Row of Inner Transition Elements)

Elements: Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr Properties:

• Filling of 5f orbitals
• All are radioactive
• Most are synthetic (not found in nature)
• Multiple oxidation states
• Used in nuclear energy and weapons

Periodic Trends

Atomic Radius

Trend:

• Decreases across a period (left to right)
• Increases down a group

Explanation:

• Across period: Increasing nuclear charge pulls electrons closer
• Down group: New electron shells are added, increasing distance from nucleus

Ionic Radius

Trend:

• Cations are smaller than their parent atoms
• Anions are larger than their parent atoms
• Similar trends to atomic radius within groups of similar ions

Explanation:

• Cations: Electron removal leaves fewer electrons for same nuclear charge
• Anions: Electron addition causes increased electron-electron repulsion

Ionization Energy

Definition: Energy required to remove an electron from a gaseous atom

Trend:

• Increases across a period (left to right)
• Decreases down a group

Explanation:

• Across period: Increasing nuclear charge holds electrons more tightly
• Down group: Valence electrons are farther from nucleus and more shielded

Electron Affinity

Definition: Energy change when a gaseous atom gains an electron

Trend:

• Generally becomes more negative across a period (left to right)
• Generally becomes less negative down a group

Explanation:

• Across period: Increasing nuclear charge attracts additional electrons more strongly
• Down group: Valence shell is farther from nucleus, reducing attraction

Electronegativity

Definition: Ability of an atom to attract electron density in a chemical bond

Trend:

• Increases across a period (left to right)
• Decreases down a group

Explanation:

• Follows similar pattern to ionization energy
• Highest in upper right of table (F, O, N, Cl)
• Lowest in lower left of table (Cs, Fr)

Metallic Character

Trend:

• Decreases across a period (left to right)
• Increases down a group

Explanation:

• Inversely related to electronegativity and ionization energy
• Metals tend to lose electrons; nonmetals tend to gain electrons

Electron Configuration Patterns

Electron Configuration Notation

• Based on aufbau principle, Pauli exclusion principle, and Hund’s rule
• Format: 1s² 2s² 2p⁶ 3s² 3p⁶, etc.
• Noble gas shorthand: [Ne] 3s² 3p⁶ for sodium

Block Classification

• s-block: Groups 1-2 (ns¹-²)
• p-block: Groups 13-18 (ns² np¹-⁶)
• d-block: Groups 3-12 (ns² (n-1)d¹-¹⁰)
• f-block: Lanthanides and Actinides (ns² (n-2)f¹-¹⁴ (n-1)d⁰-¹)

Valence Electrons and Chemical Behavior

• Main group elements: Number of valence electrons equals group number (1A-8A system)
• Transition metals: (n-1)d electrons contribute to variable oxidation states
• Elements in the same group have similar chemical properties due to similar valence configurations

Anomalous Patterns and Exceptions

d-Block Anomalies

• Chromium: [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s²
• Copper: [Ar] 3d¹⁰ 4s¹ instead of [Ar] 3d⁹ 4s²
• Due to stability of half-filled or completely filled d-subshells

Other Anomalies

• Lanthanide contraction: Causes similarity in size between 4d and 5d elements
• Post-transition metal behavior: Elements like Ga, In, Tl, Sn, Pb, Bi show some properties different from typical metals
• Diagonal relationships: Li similar to Mg, Be similar to Al, B similar to Si

Element Abundance and Occurrence

Most Abundant Elements (Earth’s Crust)

1. Oxygen (O): 46.6%
2. Silicon (Si): 27.7%
3. Aluminum (Al): 8.1%
4. Iron (Fe): 5.0%
5. Calcium (Ca): 3.6%
6. Sodium (Na): 2.8%
7. Magnesium (Mg): 2.1%
8. Potassium (K): 2.6%

Most Abundant Elements (Human Body)

1. Oxygen (O): 65%
2. Carbon (C): 18%
3. Hydrogen (H): 10%
4. Nitrogen (N): 3%
5. Calcium (Ca): 1.5%
6. Phosphorus (P): 1.0%

Essential Elements for Life

• Bulk elements: C, H, O, N, P, S, Na, K, Mg, Ca, Cl
• Trace elements: Fe, Zn, Cu, Mn, I, F, Se, Mo, Co, Cr

Practical Applications of Groups

Industrial Elements

• Catalysts: Pt, Pd, Ni, Fe, V
• Structural metals: Fe, Al, Ti, Cu
• Semiconductors: Si, Ge, Ga
• Nuclear power: U, Pu
• Batteries: Li, Pb, Ni, Cd

Modern Technology Elements

• Electronics: Si, Ge, Ga, As, Cu, Au, Ag
• Rare Earth Magnets: Nd, Sm, Dy
• Display technologies: In, Y, Eu, Tb
• Solar cells: Si, Ga, As, Cd, Te
• Batteries: Li, Co, Ni, Mn

Quick Reference: Oxidation States by Group

Memorization Tips and Tricks

Group 1 (Alkali Metals)

“Little Naughty Kids Rbobbing Cstores Frantically”
(Li, Na, K, Rb, Cs, Fr)

Group 2 (Alkaline Earth Metals)

“Bertha, Mgrandmother Came Srunning Backwards Rapidly”
(Be, Mg, Ca, Sr, Ba, Ra)

Group 17 (Halogens)

“Friends Clapping Brightly Ignite Atmosphere”
(F, Cl, Br, I, At)

Group 18 (Noble Gases)

“Helen Never Argues Krazy Xenophobic Rnonsense”
(He, Ne, Ar, Kr, Xe, Rn)

First Row Transition Metals

“Scandalized Tigers Very Crazy Mnuscles Ferociously Coerce Nickels Customers Znippingly”
(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)

Remembering Trends

• “SANE”: Size, Activity, and Number of Electrons decrease left to right
• “GAINS”: Going Across Increases Nuclear Strength
• “WID DUN”: When In Doubt, Diagonal Up for electronegativity/reactivity comparisons

Resources for Further Learning

Online Resources

• Royal Society of Chemistry Interactive Periodic Table (www.rsc.org/periodic-table)
• WebElements (www.webelements.com)
• PTable (www.ptable.com)

Educational Apps

• Periodic Table by Royal Society of Chemistry
• Merck PTE HD (Periodic Table of Elements)
• The Elements by Theodore Gray

Reference Books

• The Elements: A Visual Exploration by Theodore Gray
• The Periodic Table: A Visual Guide to the Elements by Tom Jackson
• The Disappearing Spoon by Sam Kean

This cheatsheet serves as a comprehensive reference for understanding the periodic table’s organization, element groups, and chemical trends. Mastering these patterns helps predict chemical behaviors and properties, providing a powerful foundation for all chemistry studies.