The Atom

Real life’s Legos®

Democritus, the Giggler

• Democritus, known in antiquity as the ‘laughing philosopher’ because of his emphasis on the value of ‘cheerfulness,’ was one of the two founders of ancient atomist theory. (Berryman, 2010)

Democritus Theory

First theory about atoms.

– Believed that atoms are indivisible, always in motion and indestructible.

– Believed that atoms reflected what they made.

John Dalton and His 2 Cents

• John Dalton – British Chemist– Late 1700s developed his theory on atoms.

– Atoms make up elements, all atoms of the same element are exactly alike, atoms join with other atoms to create new substances.

Dalton’s Model

Dalton’s Changes

• Dalton added that different atoms can join together to create new substances.

• He also created a model of an atom.

Hey Atoms are made of stuff!

• J. J. Thomson discovers that atoms are made up of smaller things.– He discovered the Electron.

Cathode Ray Experiments

• How these particles were discovered.

Proton and Electron

• Electron– Negatively charged subatomic particle – Much smaller than the rest of the atom.

Rutherford’s Discovery

• Ernest Rutherford discovered the nucleus.– This is the very center of the atom.– He also proposed that electrons orbit around the

nucleus much like the planets orbit the sun.– This model was called the planetary model.

The Planetary Model

Basic Atomic Structure

http://chemwiki.ucdavis.edu/Physical_Chemistry/Atomic_Theory/Sub-Atomic_Particles

Basic Atomic Structure

The Nucleus is the center of the atom.

Positively charged protons are found here.

Neutral particles called neutrons

The Strong Force

Like charges repel so how does the nucleus hold together?

The Strong Force

• The Neutron’s Strong force holds the nucleus together.

Basic Atomic StructureElectrons orbit around the atom in the electron cloud.

My How Things Change

• The modern theories about atoms have changed.– Electrons do not orbit around the nucleus in fixed

patterns, and protons are made up of smaller particles.

– Electrons instead orbit the nucleus in orbitals.

Electron Orbitals

• Electrons move extremely fast.

• They cannot be exactly located.

• They orbit in orbitals.

Electron Orbitals

• Elements have multiple orbitals starting with the “1s” orbital. This orbital only holds two electrons.

• All elements want to have a full orbital, or 8 valence electrons.

• All the elements in group 18 have 8 valence electrons. That is why they do not bond with other elements.– Helium has a full orbital with 2 electrons.

Hmm…. They are made of more stuff

• Through research at the Large Hadron Collider(LHC) Protons have been split.

• This revealed quarks. – Up, Down, Strange, Top, Bottom, and Charm.– Up and Down make protons.

How do Atoms make Matter?

• An atoms composition creates certain matter.

• The number of Protons and Electrons causes atoms to behave in certain ways.

Real Life Legos®

• A Hydrogen atom, has 1 proton and 1 electron.

• An atom that has 2 protons and 2 electrons is not the same as Hydrogen. That is Helium.

Real Life Legos®

• Helium has many qualities that differ from Hydrogen:– Nonflammable, glows when electric current is ran

through it, and it is expensive to get.– Hydrogen is extremely flammable, reactive, and

extremely abundant and cheap.

Real Life Legos®

• What if an atom had 20 protons, or 40, or even 100?

• Would these materials have the same physical characteristics? Chemical?

• How does the number of protons and electrons affect the characteristics of the atom?

Real Life Legos®

• What about neutrons?

• An atom can have different numbers of neutrons without drastically changing the characteristics of the substance.

• These are called isotopes.

Isotopes, the same or different?

• An isotope can become unstable releasing energy as the element breaks down.– Uranium 235 is enriched

The Atomic File Cabinet

• Dmitri Mendeleev noticed there was a regular repeating pattern if the elements were arranged in a certain way.

• He noticed that the characteristics of the elements he organized repeated every 18 elements.

The Atomic File Cabinet

• When something repeats at a regular pattern this pattern is a periodic pattern.

• He used the atomic mass of the elements to arrange the elements. – He noticed that certain characteristics repeated

periodically when arranged this way.

The Atomic File Cabinet

• Mendeleev predicted that as more elements were discovered his table would continue to repeat periodically, but new elements did not quite fit the pattern.

• Henry Moseley took Mendeleev’s table and used atomic number, instead of atomic mass. When he did this the table worked perfectly.

The Periodic Table

Types of Elements

• Metals– Shiny, usually solid at room temp., conduct

electricity and heat, malleable, and are ductile. • Metalloids – Have properties of both metals and nonmetals.

• Nonmetals– Are just the opposite of metals.

Group These Elements

• Group these elements based on what you know now.– Helium, Bromine, Iron, Magnesium, Oxygen,

Carbon, Aluminum, Mercury, Fluorine, Gold

Groups of elements

Groups of elements

• Group 1 elements are called Alkali Metals– Very Reactive – Have only one Valence Electron, or one electron

in their outer orbitals. – Very soft, can be cut with a knife.

• Group 1 Videos**

Groups of elements

• Group 2 Alkaline Earth Metals– Not as reactive as the Alkali Metals.– These have two Valence Electrons.