Periodic Table, Bonding, and Reactions – Study Notes

1. Periodic Table Patterns

  • Patterns in the periodic table are caused by electrical attraction and repulsion between protons and electrons.

  • These patterns help determine an element’s reactivity (how likely it is to react).

2. Predictable Patterns You Should Know

You should be able to identify and predict:

  • Number and types of bonds an element can form

  • Ion charges within the same group (column)

  • Trends across the periodic table:

    • Atomic size: increases down a group, decreases across a period

    • Electronegativity: increases across a period, decreases down a group

    • Reactivity:

      • Metals → more reactive down a group

      • Nonmetals → more reactive up a group

3. Valence Electrons & Bonding

  • Valence electrons are the outermost electrons.

  • The number of valence electrons determines:

    • How many bonds an atom can form

    • Whether it will gain, lose, or share electrons

  • Electronegativity affects how electrons are shared in a bond.

4. Using the Periodic Table

  • You can use the periodic table to:

    • Identify valence electron configurations

    • Predict how atoms combine during reactions

5. Conservation of Matter

  • Atoms are conserved in chemical reactions.

  • The number of each type of atom is the same before and after a reaction.

6. Reactants and Products

  • Reactants: starting substances

  • Products: substances formed

  • You should be able to:

    • Identify reactants and products

    • Write their chemical formulas

    • Identify the bonding types involved

7. Explaining Reaction Behavior

  • Periodic table patterns (ex: alkali metals being very reactive) help explain:

    • Why reactions happen

    • Why some elements react more strongly than others

8. Types of Bonds

You should be able to justify bond types using valence electrons and electronegativity:

  • Ionic: electron transfer (metal + nonmetal)

  • Covalent: electrons shared (nonmetals)

    • Polar covalent: unequal sharing

    • Nonpolar covalent: equal sharing

  • Metallic: shared electrons among metals

9. Revising Explanations

  • Be able to change or improve explanations if new evidence or information is given.

  1. Covalent bond:
    A bond where two atoms share electrons and are attracted to the shared electrons between their nuclei.

  2. Ionic bond:
    A bond formed when oppositely charged ions attract each other due to electrostatic attraction.

  3. Electronegativity:
    An atom’s ability to attract electrons in a chemical bond.

  4. Molecule:
    Two or more atoms chemically bonded together, usually by covalent bonds.

  5. Conservation of matter:
    Atoms are not created or destroyed in a chemical reaction; the number of each atom stays the same before and after the reaction.

Why polarity matters

  • Water is polar, so it interacts best with polar molecules.

  • Polar substances dissolve in water; nonpolar (hydrophobic) substances do not.

  • Rule: “Like dissolves like.”

How to determine if a molecule is polar or nonpolaR

  1. Calculate electronegativity difference (ΔEN) for each bond

  2. Identify lone pairs of electrons

  3. Look at molecular shape (net dipole)

    • Symmetrical molecules → nonpolar

    • Asymmetrical molecules → polar

    • Large molecules: depends on how many polar vs nonpolar regions they have and where they are located

Electronegativity Difference (ΔEN) & Bond Type

  • ΔEN ≈ 0–0.5 → Nonpolar covalent

  • ΔEN ≈ 0.5–1.7 → Polar covalent

  • ΔEN ≥ 1.7 → Ionic

Examples:

  • Cl–Cl → nonpolar covalent

  • H–Cl → polar covalent

  • Na–Cl → ionic

Bond Polarity in Glucose

  • Glucose (C₆H₁₂O₆) is polar

  • Mostly made of polar covalent bonds

  • Can form hydrogen bonds with water, so it dissolves easily

Important ΔEN values in glucose:

  • C–O → ΔEN = 1.0 → polar covalent

  • O–H → ΔEN = 1.4 → polar covalent

  • C–H → ΔEN = 0.4 → nonpolar covalent

Key idea about glucose

  • Many –OH (hydroxyl) groups make glucose very polar

  • These polar regions interact strongly with water

Big Takeaways

  • Bond polarity depends on electronegativity difference

  • Molecular polarity depends on bond polarity + shape

  • Molecules with many O–H or C–O bonds are usually polar and water-soluble

How to Find Electronegativity Difference (ΔEN)

Step 1: Look up electronegativity values

Use the periodic table (Pauling scale). Common ones you’re using:

  • H = 2.1

  • C = 2.5

  • N = 3.0

  • O = 3.5

  • Si = 1.8

  • Al = 1.5

Step 2: Subtract the values

Always subtract the smaller number from the bigger one:

\Delta EN = |EN_1 - EN_2|

Step 3: Compare ΔEN to the scale

  • 0–0.5 → nonpolar covalent

  • 0.5–1.7 → polar covalent

  • ≥ 1.7 → ionic