The Periodic Table:

Organizing the Elements

Dmitri Mendeleev (1834-1907)

constructed the first periodic table

he listed the elements in columns in order of increasing atomic mass

he arranged the elements according to similarities in their properties

Henry Moseley (1913)

a British physicist who determined the atomic number of the atoms of the elements

he arranged the elements in a table by order of atomic number instead of atomic mass

The Modern Periodic Table PERIODS - the horizontal rows of elements in the periodic table

Groups

GROUP – the vertical column of elements in the periodic table ( 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A)

Group A Elements

Group A elements are called REPRESENTATIVE

ELEMENTS divided into 3 broad classes

METALLOIDS NONMETALS METALS

Metals

1) METALS - have high electrical conductivity - high luster when clean - ductile ( can be drawn into wires) - malleable ( can be beaten into

thin sheets)

Metals

Group 1A – Alkali Metals (color them green)

Group 2A- Alkaline Earth Metals (color them pink)

Group B - Transition Metals & Inner Transition Metals ( Lathanide & Actinide Series) (color them orange)

Nonmetals

2) NONMETALS - occupy the upper-right corner of

the periodic table - they are non-lustrous and poor

conductors of electricity

Nonmetals

Group 7A – Halogens (color them blue)Group 0 - Noble Gases (color them

purple) (inert and undergo few chemical reactions)

Metalloids

3) METALLOIDS - elements that are intermediate between metals and non-metals (Ex. Silicon and Germanium)

Review- group names

List an element that will have similar properties to Lithium.

Question

Why do elements in a group have similar properties?

Elements in a group have similar electron configurations.

Electron configuration- refers to how electrons are arranged around the nucleus.

Energy levels

Energy Level- a layer or blanket of electrons

Also referred to as an electron shell.

Shells near the nucleus have less energy.

Shells further away have more energy.

Question

How are shells filled

Answer

Shells with lower energy fill up first. Followed by outer shells.

1st shell = space for two electrons 2nd shell= space for 8 electrons 3rd shell= space for 8 electrons

Valence shell- the outermost energy level of an atom.

Contains the electrons that form chemical bonds

Group number are the valence electron

Question

How do I figure out the number of shells on an atom?

Answer

Each period adds another energy level.Ex: Element in period (row) 3 have

three layers of electrons.

How many energy levels does How many energy levels does nitrogen have?nitrogen have?

Answer

Nitrogen is found in peroid 2 so it has 2 energy level

Question

How do I figure out how many valance electrons an element has?

answer

You look at the column number. 1A, 2A, 3A Count the boxes from left to right (skipping the

transition metals)

Valence electron

All elements in a column have the same number of valence electrons Thus they behave the same.

How many valance electrons do How many valance electrons do alkali metals have?alkali metals have?

Answer

Alkali metal are group one elements thus has one electron on the outer energy level

One valance electron

Lewis Dot diagram

Valence electrons are the most important in forming chemical bonds.

Lewis dot diagrams show only the valence electrons as dots surrounding the element symbol.

Example

Chlorine is a group 7 element

It has 7 valence electron

Cl

Cl

Question

How are the dots placed around the element

Answer

Electron are place around the element from the top in a clockwise direction

Octet Rule

The octet rule is a simple chemical rule of thumb that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells,

Giving them the same electronic configuration as a noble gas.

Electron Dot

Electron should be placed initially as lone pairs: one pair of dots for each pair of electrons available. Lone pairs should initially be placed on outer side of the element

Periodic Trends

Atomic radii- the size of an atom From top to bottom atoms get bigger

Why? More layers of electrons

From left to right- Get smaller Why? More protons pull the electrons closer.

Atomic Radii

Electronegativity

Electronegativity- ability to take electrons from another atom. From top to bottom- gets weaker From left to right gets stronger-

Electronegativity

Electronegativity

Why do we care? Metals lose valance electrons Nonmetals take electrons Ionic bonds

Covalent bonds Atoms near each other share electrons Non-metal with nonmetal