Unit 3 Periodic Table

James HutchisonROHS

• Development of the Periodic Table– By the mid-1800s, about 70 elements were known– Dmitri Mendeleev ordered the elements in columns in order of

increasing atomic mass in the very 1st periodic table

• In 1913, Henry Moseley determined the atomic number of atoms of elements, and used increasing atomic number to re-order the periodic table. It still stands today.

• The Modern Periodic Table– The horizontal rows are known as periods

• There are 7 periods• Properties of elements change as you move across each

period– Gives rise to the periodic law– When elements are arranged in increasing atomic number, there

is a periodic repetition of their physical and chemical properties

– The vertical columns are called groups• There are 18 groups, or families• Elements in groups have similar physical and chemical

properties

• Groups are given a number and a letter– The letters, A and B, signify properties– Group A elements are called the representative elements

because they exhibit a wide range of physical and chemical properties

– Group B are the transition elements

1A

2A 3A 4A 5A 6A 7A

8A• Elements in the 1A-7A groups are

called the representative elements outer s or p filling

The group B are called the transition elements

These are called the inner transition elements, and they belong here

• The periodic table consists of 3 main types of elements: metals, non-metals and metalloids

• Metals– Make-up 80% of all elements– High heat and electrical conductivity– High luster, ductility and malleability– Alkali metals, alkaline earth metals (Gr.A)

• Alkali Metals are the metals in Group 1A• Alkaline Earth Metals are in Group 2A

– Transition metals and inner transition metals (Gr.B)• Inner transition metals are also called rare-earth metals

Group 1A are the alkali metals (but NOT H)

Group 2A are the alkaline earth metalsH

• Non-metals– Upper right corner of the periodic table– Poor conductors – Low luster, ductility and malleability– Many exist as gases at room temperature– Two Special groups: Halogens & Noble Gases

• Halogens are in Group 7A• Noble Gases called inert gases are in Group 0 or 8A

• Group 8A are the noble gases• Group 7A is called the halogens

• Metalloids– Consists of elements with properties that

are intermediate between those of metals and non-metals

Periodic TRENDS• Ionization energy

– The energy required to overcome the attraction of the nuclear charge and remove an electron from a gaseous atom is the ionization energy

– The first ionization energy generally decreases as you move down a group

• Electronegativity– Electronegativity is the tendency for an atom to attract electrons

when they are chemically combined with atoms of another element

– Measured in units of Paulings– Electronegativity generally decreases as you move down a group– As you move across a period from left to right, electronegativity

of the representative elements increases

The arrows indicate the trend: Ionization energy and Electronegativity INCREASE in these directions

• Trends in atomic size– Atomic radius is ½ the distance between the nuclei of

two like atoms in a diatomic molecule– Atomic radius indicates relative size (usually measured

in picometers)– Atomic size usually increases as you move down a group– Electrons are added to successively higher energy levels– The shielding of the nucleus by electrons increases

(shielding effect)– Overcomes the shrinking effect caused by the increasing

charge of the nucleus

• Trends in ionic size– Atoms of metallic elements have low ionization energies and

they form positive ions easily– Atoms of non-metallic elements readily form negative ions– The loss or gain of electrons affects the size of the ions

formed– Going from left to right across a period, there is a gradual

decrease in the size of positive ions (cations)– Beginning with Group 5A, the negative ions (anions)

gradually decrease in size as you continue to move right– The ionic radii of both cations and anions increase as you

move down a group

Atomic size and Ionic size increase in these directions:

• Electron Affinity– The electron affinity is a measure of the energy

change when an electron is added to a neutral atom to form a negative ion.