The Structure of Atoms

The Basic Building Block of Matter (TEKS 8.5A)

The Particle Theory of Matter

• Matter is made of particles that are in constant motion, these particles have space in between them.

• Every kind of matter is made of one or more element(s)

• Atoms are the smallest particle of an element

Elements• Elements are the building blocks of

all matter

• An element is a pure substance that cannot be broken down any further and still retain its properties

• The term 'element' is used to describe atoms with specific characteristics.

• The periodic table is a graphic organizer of all of the elements

Elements• There are currently 118 elements (so far) that

have been identified though only 92 of them are naturally occurring.

If you could see an atom

• Just how small is an atom? (video length – 5 min)

Location, Location, Location

There are 3 main “parts” of an atom -

Draw a quick scientific sketch of where these 3

subatomic particles are located:

Add to your diagram -

Protons = + charge

Neutrons = no charge

Electrons = - charge

Bohr model shown isn’t an accurate model,

but it used to simplify the concept of an atom

How are Atoms structured?Atomic Structure

• Atoms are composed of 2 regions:

– Nucleus: the center of the atom that contains the mass of the atom

– Electron cloud: region that surrounds the nucleus that contains most of the space in the atom

– The electron doesn’t “orbit”, it constantly moves within this cloud!!

NucleusElectron

Cloud

What’s in the Electron Cloud?

• The 3rd subatomic particle is found in a cloud that surrounds the nucleus of an atom

– Electron: the subatomic particle with a negativecharge and very little mass

– Within the cloud, electrons are arranged by the amount of energy they have . These levels are called “shells” or levels.

– We will discuss this last fact more

thoroughly another day

How do the subatomic particles balance each other?

• In a neutral atom:

– The number of protons = the number of electrons

– The charges are balanced, so it is called neutral

– The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

Do the particles ever get unbalanced?

• Yes! These are called “Ions”:

– An ion is an atom with a charge

– Cation – an ion with a positive charge• Cations form when a neutral atom loses electrons

• There will be a number and/or a + sign next to the symbol

Negative Charges:

• Ions:

– an anion is an ion with a negative charge• Anions form when a neutral atom gains electrons

• There will be a number and/or a - sign next to the symbol

Hydrogen in a Periodic Table square.

Draw this in

miniature on your page!

1

H1.008

Atomic

number

(proton

number)

Elemental

symbol

Atomic

Mass

HydrogenElement

name

Underneath your square, write down these terms:

• Atomic Number: number of protons in an atom’s nucleus. Hydrogen has an atomic number of 1, because each of its atoms contains just one proton

• Elemental/Chemical Symbol: the one or two letters to represent that element

• Atomic Mass: the (average) mass of one atom of that element. Measured in amu (atomic mass units)

A few more:

• Isotope - If an element has a different number of neutrons

• Mass number – total number of protons and neutrons

How to find the number of each type of particle

• # Neutrons = Atomic Mass Number - Proton Number

• # Protons = atomic number

• # electrons:

– In neutral atoms, # Electrons = # Protons

– In ions, # Electrons = # Protons - (Charge)

– You can have a + or – charge!!

Summary (if time)!

Meet the Atom:

https://www.youtube.com/watch?v=8ypo6wGqIGY

Introduction to Atomic Structure:

https://www.youtube.com/watch?v=EMDrb2LqL7E