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.
What is the periodic table? The periodic table is arranged by increasing atomic number from hydrogen to element 118. What is the atomic number?
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.
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.
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.
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?
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
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
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.
Warning Warning Warning The periodic table that we talk about is not the only periodic table of elements.
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.
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.
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.
Chemical changes take for effort to reverse – another chemical reaction. Changing H 2 and O 2 back into water is expensive and delicate.
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. 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 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 (SiO 2 ) Semiconductors (also make with Germanium)
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
Phosphorus Key ingredient in DNA Glow in the dark
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