Atomic Theory

Atoms are the smallest unit of matter and make up everything in the universe.

Every atom is made up of three different subatomic particles:

1. Protons2. Electrons3. Neutrons

The central region of the atom is called the nucleus and consists of protons and neutrons.

Electrons orbit the nucleus in ring-like areas called electron orbitals.**

Protons = positive chargeElectrons = negative chargeNeutrons = neutral charge

**orbitals show where an electron MIGHT be.

The periodic table is used to organize elements based on their physical and reactive characteristics/trends.

Groups = vertical columns Periods = horizontal rows

Using the Periodic TableThe periodic table can be used to find

information about the various elements.

Atomic MassAverage sum of

# of protons+

# of neutrons

(average weight)

Atomic NumberNumber of protons an atom has.

Most atoms are electrically neutral, which means that the # of protons = # of electrons

Atomic MassAverage sum of

# of protons+

# of neutrons

(average weight)

Atomic NumberNumber of protons an atom has.

Symbolic Notation

Oxygen

OX

Z

A

Atomic Mass Rounded

Atomic Number

ElementChlorine

Cl

Name Mass Charge Location

Proton (P+) 1 amu +1 Nucleus

Electron (e-) 1/2000 ≈ 0 -1 Orbital

Neutron (No) 1 amu 0 Nucleus

Parts of an atom

• 1 protons or 1 neutrons = 1 atomic mass unit (amu)

• 1 amu = 1.66 x 10-30 g• electrons have negligible mass

Parts of an atom

The Bohr model is a model used to show how electrons are organized in orbitals around the nucleus.Each circle around the nucleus represents an orbital. Each orbital is able to hold a certain number of electrons.

#1 – 2 electrons#2 – 8 electrons#3 – 8 electrons

#4 – 2 electrongs

Electrons fill in orbitals from the inside outwards

Valence electrons are electrons that fill the outermost shell of an atom. All atoms want to have a full outer layer and will undergo reactions to receive or give away electrons.

HW = Fill out Bohr Model Sheet for first 21 elements.

Review Q’s1. Where is the proton located?2. What is the charge and mass of a neutron?3. How many protons, electrons and neutrons

are in the following?a) Hb) Clc) Cd) Fe-2

4. Draw the Bohr model for the Oxygen