Group 1 - Alkali Metals

Group 1 elements properties are characterized by their high reactivity and distinctive physical characteristics. These elements, also known as alkali metals, share similar properties due to their single outer shell electron configuration.

Physical properties of Group 1 elements include:

• Soft metals that can be easily cut with a knife
• Low densities and low melting points
• Increasing softness down the group

Chemical properties of Group 1 elements include:

• High reactivity due to the ease of losing one electron
• Formation of 1+ ions during reactions
• Increasing reactivity down the group

Definition: Alkali metals - Highly reactive metallic elements in Group 1 of the periodic table, characterized by a single valence electron.

Highlight: Trends in Group 1 melting point show a decrease as you move down the group, due to weaker forces of attraction between the nucleus and the outer electron.

Group 1 reactivity increases down the group because:

• The number of electron shells increases
• The outer electron is further from the nucleus
• Less energy is required to remove the outer electron

Example: The alkali metals in order of increasing atomic number are: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr).

Group 7 - Halogens

The halogens, located in Group 7 of the periodic table, exhibit unique properties of Group 7 elements that distinguish them from other groups.

Physical properties of Group 7 elements include:

• Non-metallic nature
• Diatomic molecular structure (e.g., F₂, Cl₂, Br₂, I₂)
• Increasing melting and boiling points down the group

Chemical properties of Group 7 elements include:

• High reactivity due to their seven outer shell electrons
• Formation of halide ions (X⁻) during reactions
• Decreasing reactivity down the group
• Ability to form ionic compounds with metals and covalent compounds with non-metals

Vocabulary: Halide ions - Negatively charged ions formed when halogen atoms gain an electron.

Highlight: The Properties and trends in Group 1 and 7 elements periodic table show opposite patterns in reactivity, with Group 1 increasing and Group 7 decreasing down the group.

A key reaction involving halogens is the displacement reaction:

Example: Cl₂ + 2KBr → 2KCl + Br₂ (Chlorine displaces bromine from potassium bromide)

This reaction demonstrates that a more reactive halogen can displace a less reactive halogen from its compounds.

Definition: Displacement reaction - A chemical reaction where a more reactive element replaces a less reactive element in a compound.

The trends in physical properties of halogens, such as increasing melting and boiling points down the group, are due to stronger intermolecular forces between larger atoms, requiring more energy to overcome these forces.