Module 2 : Atomic Theory and Periodic Table

Atomic Theory

The historical concept that matter is made up of tiny, indivisible particles called atoms.

Democritus

He gave the first idea of the composition of matter which is ATOM.

Atom

It is the smallest indivisible and indestructible particle of matter.

A-tomos

It is a Greek word which means not to cut or cannot be cut.

John Dalton

He is a English chemist that developed the first modern theory of atom.

John Dalton’s Atomic Theory summarized as follows:

1. Matter consists of tiny indestructible particles called *atoms*.
2. Atoms of the *same elements* are all alike.
3. In *chemical reactions*, the combination of atoms may break down but the atoms themselves are unchanged.
4. When *atoms form molecules*, they unite in small whole numbered ratio such as 1:1, 2:1, 2:3, and so on.

Joseph John Thomson and Julius Plucker

They discovered Electron (e-).

9\.107 x10^-28 g

What is the mass of Electron (e-)?

Electron

It is located in the main energy level/shell or outside the nucleus.

Eugene Goldstein and Ernest Rutherford

They are the one who discovered Proton (p+).

1\.677 x10^-24 g

What is the mass of Proton (p+)?

Protons (p+) and Neutrons (n^0)

They are located in the nucleus.

James Chadwick

Who discovered Nucleus (n^0)?

1\.675 x10^-24 g

What is the mass of Neutron (n^0)?

Nucleus

It is small massive structure located at the center of an atom.

Electron Cloud

Main energy levels or shells can also called as __________?

Atomic Number

The number of protons in the nucleus of an atom, which is also equal to the number of electrons in the atom.

Atomic Weight

It represents the relative *weight of an atom* of an element with weight of one atom of carbon conventionally taken as equal to 12.

Number of Neutrons

Atomic weight minus atomic number (no. of protons and electrons) is equal to ______?

Isotopes

They have the same number of protons but different number of neutrons are called ________?

Main Energy Levels or Shells

The orbits where the electrons revolve around nucleus are called _____?

Sublevels

The different types of subshells within an energy level, designated as s, p, d, and f.

s (sharp) = 2

p (principal) = 6

d (diffuse) = 10

f (fundamental) = 14

What are the are the number of electrons does s p d f sublevels or subshells have?

s = 1, p = 3, d = 5, f = 7

How many orbitals does s p d f have?

Electron Configuration

It is a systematic arrangement of electrons in the main energy levels and sublevels of an atom.

The Pauli Exclusion Principle

It is a principle that the limits of number of electrons in *any orbital to not-more than two*, and this pair of electrons must *spinning in opposite direction.*

The Hund’s Rule or Principle of Maximum

It is a rule that each orbital must be occupied with a single electron before pairing of electrons in any orbital of that sublevel can occur.

Two Methods in Illustrating Electron Configuration

1. s p d f Method
2. Rectangular Arrow Method or Arrow

s p d f method

It is a method of distributing the electrons indicating the filling of the energy levels and sublevels.

Rectangular Arrow Method or Arrow

It is a box method that uses arrow to represent electrons and boxes for orbital. The Pauli Exclusion Principle and Hund’s Rule are strictly followed in this method

Three Different Methods in Diagramming Atomic Structure

1. Complete Atomic Structure
2. Ionic Method or Half-shell Notation
3. Electron-dot Notation or Lewis Structure

Complete Atomic Structure

It shows the proton and neutron in the nucleus and the electrons found outside the nucleus rotating in a definite path called shells or main energy levels around the nucleus.

Ionic Method or Half-shell Notation

It shows the symbol of the element and how the electrons are placed

in the different main energy levels represented by the half-shell.

Electron-dot Notation or Lewis Structure

It shows the nucleus represented by the symbol of the element and the valence electron distributed around the symbol by means of dots or dashes.

Periodic Table

A systematic listing or arrangement of elements in order of increasing atomic number.

Periods (other terms: Energy and Series)

The elements are arranged in horizontal rows and designated by numbers 1-7.

Group or Families

The vertical column, which divided into to A & B subgroups.

1800

The year that chemist began to determine the atomic weights of some elements.

Dimitri Mendeleev (1834-1907)

He worked out the periodic table of elements. He arranged the elements in order of their increasing atomic weights, the lowest is Hydrogen and the highest is Uranium.

Dimitri Mendeleev (1834-1907)

In 1890’s, he added an additional element to each period. He left spaces for elements that might some day discovered. He studied the properties of the elements and predicted the properties of would be discovered elements.

Henry Moseley (1887-1915)

He is a young English scientist that used the x-ray to determine the atomic numbers (proton) of the elements.

Henry Moseley (1887-1915)

He concluded that the elements should be arranged in the order of increasing atomic numbers

X-ray

It is the light radiation with high frequency and short wave length.

Moseley found…

* The higher the atomic number the shorter the wave lengths of x-rays, when that element is used as a target.
* In some cases, unusual variations between two successive elements.

Periodic Law

It states that some of the physical and many of the chemical properties of the elements are periodic functions of their atomic numbers.

Periodic Table

* The elements are arranged according to increasing atomic numbers in the table.
* This lists the elements with their symbols, atomic numbers, atomic weights, and so forth.
* It is composed of 18 vertical columns and 7 horizontal rows.

Metals

* These elements are mostly solids, have a luster, and can conduct electricity and heat.
* They have high density, high melting and boiling points, and can also combine with non-metals to produce salts.
* They can be found on the left side of the periodic table.

Mercury (Hg)

Metals are mostly solid except ______, which is liquid at room temperature.

Non-metals

* These elements have poor electrical and thermal conductivity, low density, and low melting and boiling points.
* Several of their elements can exist as gases at room temperature. T
* hey can also be found on the right side of the table.

Metalloids

* The amphoteric elements border the darkline. These are dull-appearing and brittle solids at room temperature.
* They can also be called semiconductors because they conduct electricity better than non-metals but not as well as metals.

Representative Elements

The elements in groups 1A through 7A of the periodic table, which have incomplete outer energy levels and occupy the s or p orbitals.

Trends in Periodic Table

1. Atomic Size
2. Ionization Energy
3. Electron Affinity
4. Electronegativity

Atomic Size

The size of an atom becomes bigger as its number of shell increases.

Ionization Energy

The amount of energy required to remove an electron form an atom.

Electron Affinity

The energy released when an electron is added to an atom, which generally increases as you move across a period in the periodic table.

Electronegativity

The tendency of an atom to attract electrons towards itself in a chemical bond, which generally increases as you move across a period in the periodic table.