Atomic Structure and Periodic Table Basics

Atomic Structure

• Protons determine the atomic number and identity of the element.
• Neutrons help glue the nucleus together, and the mass number is the sum of protons and neutrons.
• Electrons are arranged in energy levels or shells, usually equal to the number of protons.

Periodic Table

• Elements are arranged in increasing order of atomic number.
• The first row has 2 electrons, and the second and third rows have 8 electrons each.
• Columns have elements with the same number of electrons in their outer shell (valence shell).

Ions

• An ion is an atom that has lost or gained electrons.
• Cations are positively charged ions (lose electrons).
• Anions are negatively charged ions (gain electrons).

Electron Configuration

• The first shell holds up to 2 electrons.
• The second and third shells hold up to 8 electrons each.
• The valence shell is the outermost shell.

Octet Rule

• Atoms tend to have a full valence shell of 8 electrons for stability.

Groups in the Periodic Table

Group 1: Alkali Metals

• Have 1 electron in the valence shell.
• Highly reactive, losing 1 electron to form +1 cations.

Group 2: Alkaline Earth Metals

• Have 2 electrons in the valence shell.
• Reactive, losing 2 electrons to form +2 cations.

Group 7: Halogens

• Have 7 electrons in the valence shell.
• Highly reactive, gaining 1 electron to form -1 anions.
• Commonly used as cleaners and disinfectants.

Group 8: Noble Gases

• Have a full valence shell.
• Not reactive and rarely form compounds.

Other Categories

• Non-metals: Diverse elements that typically gain electrons.
• Transition Metals: Metals with varying properties.
• Metals: Majority of elements, tend to lose electrons.
• Flame Test for Metals: Identifies metals based on the color of light emitted when heated.

Chemical Bonding

Chemical Bonds

• Elements combine to form chemical bonds to achieve stable or full outer electron shells.
• In a compound formula, subscripts indicate the number of each type of atom.

Types of Bonding

• Ionic Bonding
• Metallic Bonding
• Covalent Bonding

Ionic Bonding

• Occurs between a metal and a non-metal.
• Metals lose electrons to become positively charged cations.
• Non-metals gain electrons to become negatively charged anions.
• Properties: Forms a rigid crystal lattice structure, high melting and boiling points, brittle, and dissociates in water to form aqueous solutions that can conduct electricity.
• Example: Sodium chloride (NaCl)

Metallic Bonding

• Occurs between metal atoms.
• Metals lose electrons, becoming cations.
• Electrons become delocalized, creating a "sea of electrons."
• Properties: Shiny, ductile, malleable, and conductive of heat and electricity.
• Example: Copper (Cu)

Covalent Bonding

• Occurs between non-metals.
• Atoms share electrons to achieve full outer shells.
• Types of bonds: Single, double, or triple bonds depending on the number of shared electron pairs.
• Can be nonpolar (symmetrical sharing) or polar (unequal sharing).
• Properties: Forms molecules, which are often gases or liquids, and can form polymers or long chains of monomers.
• Examples: Water (H2O), hydrocarbons (e.g., octane C8H18)
• Polymers and Fractional Distillation: Polymers are long chains of monomers (e.g., polyethylene, polystyrene), and hydrocarbon fuels are separated by fractional distillation based on boiling points.