Atomic Theory and Chemical Bonding Fundamentals

Dalton's Atomic Theory

Dalton's atomic theory states that material is made up of very small, indivisible particles called atoms. Atoms of the same element have the same mass and chemical properties. The formation of each compound is the union of atoms of different elements.

Evolution of Atomic Models

Thomson Model (1897)

The atom is electrically neutral and consists of a solid sphere of positive charge in which the electrons are embedded.

Rutherford Model

Most of the atom is empty space. In its center, the nucleus concentrates the positive charges and most of the mass of the atom.

Bohr Model

The atom consists of a compact nucleus with a positive charge and a shell where the electrons are distributed. The electrons are organized in layers: 2 electrons in the 1st layer, 8 electrons in the 2nd, and 18 electrons in the 3rd.

Electrification and Half-life

A body can be electrified through friction, contact, or induction.

Half-life: This is the time it takes for a large number of nuclei of the same type to disintegrate by half.

Classification of Elements

Metals

Metals are good conductors of heat and electricity. They show a characteristic luster and are malleable and ductile. They tend to lose electrons and form positive ions.

Non-metals

Non-metals are bad conductors of heat and electricity. At room temperature, they can be found in any state. They tend to gain electrons and form negative ions.

Noble Gases and Hydrogen

Noble gases exist as isolated atoms. They are very stable chemically and do not form compounds. Hydrogen is unique; it is not a metal nor is it part of any specific group.

Periodic Table Groups

• Alkaline: Last level has 1 electron.
• Alkaline earth: 2 electrons.
• Boron group: 3 electrons.
• Carbon group: 4 electrons.
• Nitrogen group: 5 electrons.
• Chalcogens (Amphigens): 6 electrons.
• Halogens: 7 electrons.
• Noble gases: 8 electrons, with the exception of helium.

Chemical Bonding and Lewis Theory

Lewis Theory

Atoms combine in order to accomplish a more stable electronic configuration. Maximum stability is achieved with the noble gas configuration.

Defining Chemical Bonds

A chemical bond is the force of attraction that holds together the particles that form a substance.

Ionic Bond

An ionic bond is the union of electrostatic attraction forces between ions of opposite signs. Metallic elements tend to lose one or more electrons from the valence band to achieve a noble gas configuration, forming cations (positive ions). Non-metallic elements tend to gain one or more electrons to achieve a noble gas configuration, forming anions (negative ions).

Covalent Bond

A covalent bond is the union of two atoms that share one or more pairs of electrons. This occurs if the tendency of atoms to lose or gain electrons does not result in the formation of similar ions.

Metallic Bond

A metallic bond is the union between positive metal ions and an electronic cloud forming a crystal lattice. The atoms of metals tend to lose electrons from the valence band and form positive ions, which constitute the structure of the crystal lattice. The electrons that have been lost form the electronic cloud surrounding all positive ions, establishing electrostatic forces of attraction.

Understanding Ions

Ions are atoms that have lost or gained electrons in the shell. They can be cations (positive ions) if they have lost electrons, or anions (negative ions) if they have gained electrons.