What is | Electronegativity | Chemical Bonding? | Ionization Energy | Atomic Radius

Definition: Electronegativity is the ability of an atom to attract shared electrons in a chemical bond.

Trend in the Periodic Table:
- Across a period (left → right): Increases (atoms have more protons, so stronger attraction for electrons).
- Down a group (top → bottom): Decreases (atoms get larger, electrons are farther from the nucleus).
Example: Fluorine is the most electronegative element (it strongly pulls electrons).

Definition: Ionization energy is the amount of energy required to remove the outermost electron from a gaseous atom.
Trend in the Periodic Table:
- Across a period: Increases (nucleus holds electrons more tightly).
- Down a group: Decreases (outer electrons are farther away and easier to remove).
Example: Helium has the highest ionization energy because its electrons are held very tightly.

Definition: Atomic radius is the distance from the center of the nucleus to the outermost electron of an atom.
Trend in the Periodic Table:
- Across a period: Decreases (more protons pull electrons closer).
- Down a group: Increases (more electron shells are added, making the atom bigger).
Example: Cesium (Cs) has one of the largest atomic radii, while Helium (He) is one of the smallest.

Summary of Trends (Periodic Table Patterns):

What is Chemical Bonding?

Definition: Chemical bonding is the process by which atoms combine together to form molecules or compounds in order to achieve stability (usually a full outer shell of electrons, also called the octet rule).
Atoms bond so they can become more stable, like noble gases.

When elements react, they do so according to certain laws:

Law of Conservation of Mass (Lavoisier):
Mass is neither created nor destroyed during a chemical reaction.
Example:

$2H_2 + O_2 → 2H_2O$

Mass of reactants = Mass of products.
Law of Constant Proportion (Proust’s Law):
A given compound always contains the same elements in the same fixed proportion by mass.
Example: Water (H₂O) always has hydrogen and oxygen in the ratio 2:16 by mass (1:8).
Law of Multiple Proportions (Dalton):
When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole-number ratios.
Example: CO (12:16) and CO₂ (12:32).

Formed by transfer of electrons from a metal to a non-metal.
Metal loses electrons (becomes cation), non-metal gains electrons (becomes anion).
Example: NaCl (Sodium chloride).

Dot and Cross Diagram (NaCl):
Na· → Cl:Cl: (with full octet around Cl, Na⁺ and Cl⁻ ions formed).

Dot and Cross Diagram (H₂O):
O has 6 outer electrons, shares 1 each with 2 H atoms → complete octet for O.

Found in metals.
Positive metal ions are surrounded by a “sea of delocalized electrons” that move freely.
This explains properties like conductivity and malleability.

Bond Type	Properties
Ionic Compounds	High melting & boiling points, conduct electricity when molten/aqueous, soluble in water, crystalline solids.
Covalent Compounds	Low melting & boiling points, poor conductors, often gases/liquids/soft solids, insoluble in water (mostly).
Metallic Compounds (Metals)	Good conductors of heat & electricity, malleable, ductile, high melting & boiling points, lustrous (shiny).

Quick Recap:

Chemical bonding = atoms combining to gain stability.
Laws of chemical combination = govern how elements react (mass conservation, constant proportion, multiple proportion).
Bond types = Ionic (transfer), Covalent (sharing), Metallic (sea of electrons).
Properties differ based on bond type.