Periodic Table, Atomic Structure, and Chemical Bonding
1. Periodic Table Basics
Key Concepts:
The periodic table arranges elements by increasing atomic number.
Periods (rows) show trends in atomic number and properties.
Groups (columns) have elements with similar chemical properties.
Historical Development:
Mendeleev organized elements by atomic weight and properties.
The modern table uses atomic number for organization.
2. Atomic Structure
Protons: Positive particles in the nucleus.
Neutrons: Neutral particles in the nucleus.
Electrons: Negative particles orbiting the nucleus.
Neutral atoms have equal protons and electrons.
3. Ions and Ionic Structure
Ions form when atoms gain or lose electrons.
Cations: Positive ions (lose electrons).
Anions: Negative ions (gain electrons).
Ionic bonds form by electrostatic attraction.
Properties of Ionic Compounds:
- Crystalline structures.
- High melting points.
- Conduct electricity when dissolved.
4. Periodic Trends
Atomic Radius:
- Increases down a group.
- Decreases across a period.
Ionization Energy:
- Decreases down a group.
- Increases across a period.
Electronegativity:
- Increases across a period.
- Decreases down a group.
Metallic Character:
- Increases down a group.
- Decreases across a period.
5. Periodic Table Groups
Group 1: Alkali Metals (reactive, one valence electron).
Group 2: Alkaline Earth Metals (less reactive).
Group 17: Halogens (reactive non-metals).
Group 18: Noble Gases (inert).
6. Valence Electrons and Bonding
Valence Electrons:
Outermost shell electrons determine reactivity.
Group number indicates valence electrons.
Octet Rule:
Atoms gain, lose, or share electrons to achieve a full shell (usually 8).
7. Types of Chemical Bonds
Ionic Bonds:
Electron transfer between metals and non-metals.
Example: NaCl (Na+ and Cl–).
Properties: High melting/boiling points, conductive in solution.
Covalent Bonds:
Electron sharing between non-metals.
Polar or non-polar.
Example: H2O.
Properties: Lower melting/boiling points, poor conductors.
Metallic Bonds:
Delocalized electrons in metals.
8. Naming Compounds
Ionic Compounds:
Cation name + anion name (-ide).
Transition metals use Roman numerals for charge.
Covalent Compounds:
Prefixes indicate number of atoms.
9. Chemical Reactions
Physical Change: Alters form, not composition.
Chemical Change: Forms new substances.
Signs: Temperature change, color change, gas, precipitate.
10. Bonding and Properties
Metallic Character: Increases down, decreases across.
Ionic Radius:
Cations are smaller.
Anions are larger.
Lewis Structures:
Show valence electron arrangement.
Dots for electrons, lines for bonds.
Rules:
- Determine valence electrons.
- Arrange atoms (least electronegative in center).
- Use dots and lines to satisfy the octet rule.
- Example: Oxygen (O)
- Example: Sodium ion (Na+)
- Example: Chloride ion (Cl–)
- Example: Water (H2O)
Multiple Bonds:
Double bonds: Two shared electron pairs.
Triple bonds: Three shared electron pairs.
Example: Carbon dioxide (CO2)
Exceptions to Octet Rule:
Hydrogen and Helium (duet rule).
11. Changes in Matter
Physical Changes: Form changes only.
Chemical Changes: New substances form.
Signs: Energy, gas, precipitate, color change.
Isotopes have same atomic number but different atomic weight.