Periodic Trends

Periodic – (adjective) – Having a repeating pattern; happening again and again. Examples: Day  Night  Day  Periodic waves washing onto a beach at regular intervals. Use patterns to predict future events or missing information – like undiscovered elements. (You do not need to write this)

How is the current periodic table organized? By Atomic Number (left to right) – # protons By Column (group or family)- elements in the same column have the same number of valence electrons – Valence electrons-the electrons in the outer most electron shell. By row (period)- elements in the same period have the same number of electron shells

Families of Elements are arranged by vertical column Families are also called groups

Down A Group All elements in the same group (vertical column) on the periodic table have the same number of outer electrons (valence electrons) The number of valence electrons is dependent on which tall column in which the atom is located. 1 st tall column =1 valence electron, 6 th tall column = 6 valence electrons. Skip the shorter “d” block (10 shorter columns in the middle.

Elements in the same family react the same way. This is because they pick up or give away the same number of electrons as other members of the family.

Why do elements react? Elements react in a way to fill the outermost shell with 8 electrons. Noble gases are said to be “perfect” the way they are because they already have 8 valence electrons-this is why they rarely react with other elements.

Give away or take electrons? In General Fewer than four valence electrons - give away More than four valence electrons - take NaClNa + Cl - Give away electrons makes the element positive (called a cation) Take electrons makes the element negative (called an anion)

Chemical Families Column 1 Li, Na, K …Alkali Metals Column 2Be, Mg, Ca …Alkaline Earth Metals Columns 3-12Sc – Zn …Transition Metals Column 13B, Al, Ga …Boron family Column 14C, Si, Ge …Carbon family Column 15N, P, As …Nitrogen family Column 16O, S, Se …Chalkogens Column 17F, Cl, Br …Halogens Column 18He, Ne, Ar …Noble Gases

Across a period All elements in the same period (horizontal row) on the periodic table have the same number of electron shells The number of shells is dependent on the period in which the element is located. Peirod 1 = 1 shell, period 5 = five shells

There are many representations of the periodic table….some look more like what you are familiar with than others.

The first periodic table

Tables/Circular-Periodic-Table.htm

A spiral form of the periodic table This example was devised by Theodor Benfey and depicts the elements as a seamless series with the main group elements radiating from the center with the d- and f-elements filling around loops.as

Metals, Non-metals and Metalloids

How could we test a sample to find out whether it is a metal, non- metal or metalloid? Most metals are not magnetic What are some of the key properties of these groups?

Metals A metal is an element that is a good conductor of heat and electricity. At room temperature, most metals are solids. Most metals are malleable ( can be hammered or rolled into thin sheets). Metals tend to be ductile (can be stretched into fine wire). Sodium CopperGold

Nonmetals A nonmetal is an element that is a poor conductor of heat and electricity. Many nonmetals are gases at room temperature One-bromine is a liquid The solid nonmetals are brittle rather than malleable and ductile. Sulfur ChlorineBromine

Metalloids A metalloid is an element that has some characteristics of metals and some characteristics of nonmetals. Metalloids are found along the stair-step line separates the metals from non-metals on the periodic table. They are semi-conductors of electricity. They are all solids and tend to be less malleable than metals but not as brittle as nonmetals Silicon Boron

When elements combine: Metal + non-metal ionic bond (lose and gain electrons-ionic compound- formula unit) Non-metal and non-metal (share electrons-covalent bond-molecule)

Other common Periodic Trends Atomic Radius – one-half the distance between the nuclei of identical atoms that are bonded together. Ionization Energy (IE)- The energy required to remove one electron from a neutral atom of an element. Electron affinity- The energy change that occurs when an electron is acquired by a neutral atom. Electronegativity- a measure of the ability of an atom in a chemical compound to attract electrons.