OzoneOzone

An allotrope of oxygen

two forms of the same element that differ in their molecular and crystal structure, and hence their properties

O2 O3Energy+3 2

Filtering Effect of the Ozone LayerFiltering Effect of the Ozone Layer

Subatomic ParticlesSubatomic Particles

There are many… more than 200!

But 3 are most significant:ElectronsNucleus

Protons

Neutrons

Properties of atomsProperties of atoms

Mainly due to thethe number and distribution of electrons

Properties of atomsProperties of atoms

Mainly due to thethe number and distribution of electrons

Electrons are arranged in levels or shells around the nucleus

Properties of atomsProperties of atoms

Mainly due to thethe number and distribution of electrons

Electrons are arranged in levels or shells around the nucleus

The electrons in the innermost shell are most strongly attracted to the nucleus

Which type of electrons determines Which type of electrons determines the “behavior” of atoms?the “behavior” of atoms?

the ones which can “interact” with other atoms.

(not the ones closest to the nucleus, in the innermost shell)

Which type of electrons determines Which type of electrons determines the “behavior” of atoms?the “behavior” of atoms?

the ones which can “interact” with other atoms.

(not the ones closest to the nucleus, in the innermost shell)

The most distant electrons (in the outermost shell) are the least attracted to the nucleus

The shells are associated with The shells are associated with energy levels:energy levels:

Each energy level has maximum electron capabilities

The shells are associated with The shells are associated with energy levels:energy levels:

Each energy level has maximum electron capabilitiesbecomes particularly stable when “filled”

The shells are associated with The shells are associated with energy levels:energy levels:

Each energy level has maximum electron capabilitiesbecomes particularly stable when “filled” The innermost level, the lowest energy

level, can hold a maximum of two electrons

How are molecules formed?How are molecules formed?

when atoms form “bonds” with one another

How are molecules formed?How are molecules formed?

when atoms form “bonds” with one another

Covalent bonds:

when two atoms “share” a pair of electrons

Step 1:

Count the number of outer electrons.

For a neutral molecule this is equal to the number of outer electrons of the constituent atoms.

How to Write Lewis StructuresHow to Write Lewis StructuresHow to Write Lewis StructuresHow to Write Lewis Structures

Step 1:

Count the number of outer electrons.

For a neutral molecule this is equal to the number of outer electrons of the constituent atoms.

Step 2: Connect the atoms by a covalent bond represented by a dash.

How to Write Lewis StructuresHow to Write Lewis StructuresHow to Write Lewis StructuresHow to Write Lewis Structures

Step 3:

Distribute the remaining electrons not involved in bonding “in pairs”

in such a way that as many atoms as possible have 8 electrons

How to Write Lewis StructuresHow to Write Lewis StructuresHow to Write Lewis StructuresHow to Write Lewis Structures