Notes lab 04 the invisible atom

The AtomThe Atom

NotesNotes

The AtomThe Atom

From the Greek prefix A- meaning“not”

And the Greek Root –tomos meaning “cut””

Together meaning “uncuttable”

The ancient Greeks wanted to learn about the smallest particle of matter

DemocritusDemocritus

Ancient Greek Model of Atoms

The ancient Greeks were one of the earliest cultures to investigate the concept of the atom.

Democtitus and Aristotle , two Greek philosophers came up with two alternate theories

Democritus’ “Atom”

Democritus Democritus believed that all matter consisted of extremely small particles that could not be divided.

He called these particles atoms (from the Greek “ατοµος”, meaning “uncut” or “indivisible”).

Democritus’ “Atom”

He believed there were different types of atoms with specific sets of properties. The atoms in liquids, for example, were round and smooth, but the atoms in solids were rough and prickly

AristotleAristotle

Aristotle’s “Atom”

Aristotle did not think there was a limit to the number of times matter could be divided.

He thought that all substances were built up from only four elements—earth, air, fire, and water. These elements were a combination of four qualities—hot, cold, dry, and wet.

Aristotle’s “Atom”

Fire was a combination of hot and dry.Water was a combination of cold and wet.

DaltonDalton

Dalton’s Model of the Atom

Dalton proposed the theory that all matter is made up of individual particles, called atoms, which cannot be divided.

All atoms of the same element have the same mass, and atoms of different elements have different masses.

Dalton’s Model of the Atom

Compounds contain atoms of more than one element.

He developed a theory to explain why the elements in a compound always join in the same way

In a particular compound, atoms of different elements always combine in the same way

The Dalton ModelThe Dalton Model

J. J. ThomsonJ. J. Thomson

J. J. Thomson’s Model of the J. J. Thomson’s Model of the AtomAtom

In Thomson’s experiments with beams of charged particles in a sealed glass tube led him to the conclusion that atoms were made of even smaller particles

Thomson reasoned that if the charge of an atom is neutral, the atom must contain particles with both positive and negative charges in equal amounts.

J. J. Thomson’s Model of the J. J. Thomson’s Model of the AtomAtom

In Thomson’s experiments with beams of charged particles in a sealed glass tube led him to the conclusion that atoms were made of even smaller particles

Thomson reasoned that if the charge of an atom is neutral, the atom must contain particles with both positive and negative charges in equal amounts.

The Thomson ModelThe Thomson Model

In Thomson’s model of the atom, the negative charges were evenly scattered throughout an atom filled with a positively charged mass of matter. The model is called the “plum pudding” model.

RutherfordRutherford

Rutherford’s Model of the Rutherford’s Model of the AtomAtom

To account for these results, Rutherford hypothesized that the positive charge of an atom must be concentrated in a very small area that he called the nucleus.

Further experiments with other elements led him to conclude that the positive charge of an atom is determined by the number of protons in the nucleus.

Each proton has a charge of +1.

Rutherford’s Model of the Atom Rutherford’s Model of the Atom and Gold Foil Test and Gold Foil Test

Niels BohrNiels Bohr

The Bohr Model of the AtomThe Bohr Model of the Atom

In Bohr’s model, electrons move with constant speed in fixed orbits around the nucleus, like planets around a sun.

Electrons gain or lose energy when they move between orbits or energy levels. Energy levels are like stairs on a staircase or shelves in a bookshelf

The Bohr Model of the AtomThe Bohr Model of the Atom

Evidence for discrete, unique energy levels comes from the light given off when energy is added to the atoms of an element (such as when fireworks explode or electricity is added to a neon light). No two elements have the same set of energy levels, so the emission pattern can be used to identify the element.

The Bohr ModelThe Bohr Model

ChadwickChadwick

Deduced the existence of neutrons from experiments in which a charged object did not deflect the path of particles he produced.

Schrodinger & Schrodinger & HeisenbergHeisenberg

Schrodinger & Heisenberg’s Schrodinger & Heisenberg’s Electron Cloud Model Electron Cloud Model

An electron in an atom can move An electron in an atom can move from one energy level to another from one energy level to another when the atom gains or loses when the atom gains or loses energyenergy.

Scientists discovered that electrons are less predictable than in Bohr’s model of fixed orbits. They use an electron cloud model to show the most likely locations for electrons as they move around the nucleus.

The electron cloud represents all the orbitals in an atom. An orbital is a region of space around the nucleus where an electron is likely to be found. Orbitals come in different sizes, shapes, and locations

An electron configuration is the arrangement of electrons in the orbitals of an atom. The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies

The Electron Cloud ModelThe Electron Cloud Model

The Nature of Science

Each scientist was correct for his time and ability to make observations.

As improvements in technology came about, each later scientist proved the previous scientist(s) slightly incorrect.

Now there is a totally different model of the atom from the first model presented by Thompson.

Only some of the theories of each scientist remain.

In general…

The Nature of ScienceThe Nature of Science

As the ability to As the ability to make better make better observations observations improves, the improves, the knowledge may knowledge may prove or disprove prove or disprove what we have held what we have held to be true in to be true in science.science.