1. C7 The Periodic Table G8 Science

2. The Periodic Table  Of the 118 elements we know about, only 88 occur naturally. The rest are make in laboratories.  The periodic table is a display of the known elements and shows how they relate to each other.

3. What is the periodic table?  The periodic table is arranged by increasing atomic number from hydrogen to element 118.  What is the atomic number?

4. Who designed the periodic table?  Scientists spent a long time trying to find a logical way to organize the elements. The breakthrough came with Dmitir Mendelev in 1869.

5. What are the parts?  The horizontal rows are called periods. The properties of elements change gradually across the period.  The vertical columns are called groups. Elements in the same group have similar properties.

6. What are the main categories?  Metals are typically shiny, opaque, ductile, and good conductors of heat and electricity.  Nonmetals are poor conductors, brittle and dull (or gasses)  Metalloids have properties between the two.

7. What is usually on a table entry?  Entries on the periodic table will contain:  Element name (maybe)  Element symbol – Capital letter with maybe a lowercase letter after it  Atomic number  Atomic mass (in amu)  What is an amu?

8. What else can be on it?  You may also find: Stable mass numbers  Count of electrons in each shell  Picture of the element  Link to element information

9. Groups on the periodic table  Alkali metals: group 1, soft, silvery, highly reactive. Combines 2:1 with oxygen Li 2 O  Alkaline Earth metals: group 2, combine 1:1 with oxygen CaO. Reactive, but less so that alkali metals.  Halogens: group 17, toxic, very reactive, seldom found in pure form, when combined with alkali metals form salts.  Noble Gases: group 18, unreactive, inert, almost always found in pure form.  Transition metals: center of table, good conductors

10. Energy levels and the periodic table  Period 1: only one shell (k), up to 2 electrons  Period 2: two shells (k, l), 2 in first, up to 8 in second  Period 3: three shells (k, l, m), 2 in first, 8 in second, up to 8 in third  Period 4: four shells (k, l, m, n) 2 in first, 8 in second, 8 – 18 in third, up to 8 in fourth.  Period 5: five shells (k, l, m, n, o)  Valence electrons are those in the outermost shell. For period 3 we only care about the m-shell.

11. Warning Warning Warning  The periodic table that we talk about is not the only periodic table of elements.

12. Physical and Chemical Properties  Physical properties are things you can see through direct observation, like density, boiling point, and melting point.  The chair seat is a dull red, flexible, low-odor flexible solid at room temperature.  Water is a colorless, odorless substance that is liquid at room temperature.

13.  Physical properties are sometimes reversible and do not create new substances.  If you cool water it becomes ice. I can heat it to make a liquid again. If you heat water it becomes steam. Both are still H 2 O  If you heat plastic it gets softer. If you cool plastic it gets brittle. If I break it I have more than one piece of plastic, but, it is still plastic.

14.  Chemical properties can be observed when an object is changed from one substance to another – when it undergoes a chemical reaction.  If you send an electric current through water, you get hydrogen gas and oxygen gas.  If you burn plastic, you get a dark solid substance and some gases.

15.  Chemical changes take for effort to reverse – another chemical reaction.  Changing H 2 and O 2 back into water is expensive and delicate.

16. 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

17.  2 of the 92 are liquids: Br, and Hg  Elements are solid when intermolecular forces are stronger than thermal motion.

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

19. 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.

20.  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.

21. 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

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

23. 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

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

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

26.  Silicon  Second most abundant element in Earth’s crust (after Oxygen)  Sand, rocks, minerals  Glass (SiO 2 )  Semiconductors (also make with Germanium)

27. Nitrogen, Oxygen, Phosphorus  Nitrogen  Colorless, tasteless, odorless  78% of Earth’s atmosphere  N 2  Boils at -196°C  Crucial to to life  Oxygen  21% of Earth’s atmosphere  46% of Earth’s crust  Crucial to life

28.  Phosphorus  Key ingredient in DNA  Glow in the dark