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

• Atoms are the smallest particle of an element

https://www.youtube.co

m/watch?v=i0sOq7EbQ

WI

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* that have

been identified though only 92 of them are naturally occurring.

*from the last page

• In December of last year, International Union of Pure and Applied Chemistry (IUPAC) announced that they had confirmed the existence of elements 113, 115, 117 and 118, filling out the until-now incomplete the seventh row of the table.

• Elements 115, 117 and 118 were created in a particle accelerator at the Lawrence Livermore laboratory in California; number 113 popped into existence in a similar way at the Riken institute in Japan. And all of them popped out almost as quickly—lasting only a few dozen milliseconds

before vanishing

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

PROTON

• Positive Charge• Located INSIDE the

NUCLEUS• Weight of 1 AMU•AMU= Atomic Mass Unit

•Protons determine an element’s identity

NeutronNot this neutron….

• Neutrons have a NEUTRAL

charge• They are located INSIDE the

Nucleus• They weigh 1 AMU (atomic

mass unit)

Electron• Electrons have a NEGATIVE charge

• They are located OUTSIDE the nucleus on energy levels/shells

• Electrons have almost no weight. 1/1836 the size of a proton.

• Electrons are not counted when weighing 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”

– 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

2 main ways an element is represented

• In the “square” of the periodic table:

• In an atom/nuclear 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:

• Atoms always have the same number of protons, but the number of neutrons can be different (and still be the same element)

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

• Mass number – total number of protons and neutrons

• Note – mass numbers are not shown on the periodic tables, but are on nuclear symbols

Atom/Nuclear SymbolThe nuclear symbol consists of three parts:

1. the symbol of the element

2. the atomic number of the element

3. the mass number of the specific isotope.

• Here is an example of a nuclear symbol:

Atom/Nuclear Symbol

• The atomic number is:

The number of protons in the nucleus of the atom

• The mass number is:

The number of protons and neutrons in the nucleus

Draw

and label

this on

your

page!

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!!

Animations

• Protons and Electrons in action

Done with notes!

• Take a moment to put your notes in Unit 2 section of your binder

• Once you have done this, get your lab notebook and title a new page: Proton and Electron Activity

• Then write down this question:

“What makes objects attract or repel each other?

Draw this chartWhat happened when you brought the following materials near each other?

Materials

Attract or Repel

Use what you know about electrons, protons, and charges to explain your

observations

charged plastic + charged skin

charged plastic + neutral desk

charged plastic + charged plastic

Proton and Electron Activity

• Students can see evidence of the charges of protons and electrons by doing an activity with static electricity.

Materials needed (per group):• Plastic grocery bag

• Scissors

• Ruler

• Follow the instructions on the lab print out page

To conclude:• Clean up materials, including lab instructions and place

back where they were.

• Under the chart in your notebook, answer these questions using what you now know about charges and electrons:

1. Why does the plastic bag pull toward your hand?

2. Why does the plastic pull towards the desk?

3. What happened when you charged the two strips of plastic and brought them near each other?