periodic trends. periodic – (adjective) – having a repeating pattern; happening again and again....

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 Elementsare 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. 1st tall column =1 valence electron, 6th tall column = 6 valence electrons.

• Skip the shorter “d” block (10 shorter columns in the middle.

Elements in the same familyreact the same way.

This is because they pick upor give away the same

number of electrons as othermembers 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

Na Cl Na+ 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 2 Be, Mg, Ca … Alkaline Earth Metals• Columns 3-12 Sc – Zn … Transition Metals• Column 13 B, Al, Ga … Boron family• Column 14 C, Si, Ge … Carbon family• Column 15 N, P, As … Nitrogen family• Column 16 O, S, Se … Chalkogens• Column 17 F, Cl, Br … Halogens• Column 18 He, 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.

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http://en.wikipedia.org/wiki/Image:Elementspiral.svg

A spiral form of the periodic tableThis 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.

http://allperiodictables.com/ClientPages/AAEpages/aaeDeskTopper.html

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 Copper Gold

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 Chlorine Bromine

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.