1. C7.2 Properties of the Elements
G8 Science

2. 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

3. 2 of the 92 are liquids: Br, and Hg
Elements are solid when intermolecular forces are stronger than thermal motion.

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

5. 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.

6. 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.

7. 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

8. 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.

9. 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

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

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

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

13. 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

14. Phosphorus
Key ingredient in DNA
Glow in the dark