C7.2 Properties of the Elements G8 Science

Room Temperature Most pure elements are solid a room temperature 11 of the 92 naturally occurring elements are gas: H, He, N, O, F, Ne, Cl, Ar, Kr, Xe, Rn

2 of the 92 are liquids: Br, and Hg Elements are solid when intermolecular forces are stronger than thermal motion.

Noble gases (group 18) are gases because their valence shell is full, with 8 electrons, and so they have a weak intermolecular force

Periodic Properties First elements have a low melting and boiling point. They increase until you reach the middle of the table, then decrease again. Melting and boiling points reflect strong intermolecular forces.

Intermolecular forces are strongest when the valence shell is half full – because a half full valence shell has the most electrons to participate in bonding.

Thermal and Electrical Conductivity Good electrical conductors allow electrons to flow easily through them. This is a property of metals. Most metals are good thermal conductors

Elements to the right of the table are good insulators, i. e Elements to the right of the table are good insulators, i.e. poor conductors.

Metals and Metal Alloys An alloy is a solid mixture of one or more elements, of which one is a metal. Steel – iron and carbon (rusts but stronger than iron) Stainless steel – iron, carbon, chromium, vanadium, manganese (does not rust) Bronze – copper, tin Brass – copper, zinc Aluminum alloys Titanium alloys

Carbon and Carbon-like Elements < .01% of Earth’s crust Most molecules that make up plants and animals are build around carbon (Organic Chemistry)

Pure carbon Diamond Graphite Tetrahedral crystal, Hardest natural substance (diamond tip drill bits) Highest thermal conductivity Graphite Sheet like Lubricant for locks and keys

Silicon Second most abundant element in Earth’s crust (after Oxygen) Sand, rocks, minerals Glass (SiO2) Semiconductors (also make with Germanium)

Nitrogen, Oxygen, Phosphorus Colorless, tasteless, odorless 78% of Earth’s atmosphere N2 Boils at -196°C Crucial to to life Oxygen 21% of Earth’s atmosphere 46% of Earth’s crust Crucial to life

Phosphorus Key ingredient in DNA Glow in the dark