Chemical Bonds and Substance Properties

Periodic Table Structure

What is the name and number of the columns in the periodic system of elements? They are called families or groups. There are 18 columns.

What is similar about elements in the same column? They have a similar electronic structure in their outermost shell.

What is the name and number of the horizontal rows in the periodic system of elements? They are called periods. There are 7 periods.

Explain what is similar about elements in the same row. They have the same number of electron shells.

Properties of Chemical Compounds

Characteristics of Ionic Compounds

• Very stable, requiring a lot of energy for the dissolution of their crystalline structure.
• Solid at room temperature.
• Do not conduct electricity in the solid state.
• Have high melting and boiling points.
• Are hard.

Characteristics of Covalent Compounds

Covalent molecules have strong bonds between atoms. Molecular covalent substances are poor conductors of electricity.

However, molecular covalent substances often have low melting points due to weak forces between molecules. Some covalent substances form crystal structures (like diamond) which are solid at room temperature, have high melting points, and are hard.

They generally do not dissolve in water and do not conduct electrical current or heat.

Properties of Metals

• Solid at room temperature, except for mercury, which is a liquid.
• Conduct electric current because electric charges (electrons) can move freely in the electron cloud.
• Are ductile, meaning they can be easily stretched into wires, like copper used in electrical installations.
• Are malleable, meaning they can be hammered into thin sheets, like aluminum or gold used for decorative purposes.
• Their ductility and malleability are due to the ability of metal atoms to slide past each other without breaking the metallic bond.
• Metallic crystals have a certain stability and relatively high melting points.
• They are generally not soluble in common solvents.

Types of Chemical Bonds

Ionic Bonds

An electron is transferred from one atom to another. For example, in NaCl, Na gives an electron to Cl, forming Na⁺ and Cl^- ions. These ions are attracted to each other due to their opposite charges. Both atoms achieve a stable electron configuration (often an octet).

Covalent Bonds

Valence electrons are shared between atoms. For example, H and Cl atoms share their valence electrons to complete their outer shells (H achieves a duet, Cl achieves an octet). HCl is formed.

Metallic Bonds

Valence electrons are delocalized and shared among many atoms, forming an 'electron sea'. This is the case for metals like aluminum.

Why Atoms Form Bonds

Atoms bond to achieve a state of lower energy and greater stability. They tend to gain, lose, or share electrons to attain the electron configuration of a noble gas, which is very stable. This tendency to achieve eight valence electrons is known as the octet rule (except for hydrogen and helium, which aim for two).