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How Our Understanding of Matter Has Changed Over Time

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Sara Desjarlais

on 2 October 2015

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Transcript of How Our Understanding of Matter Has Changed Over Time

Stone Age Chemists
First Chemist lived before 8000 B.C
Learned to control fire to create new materials - This era was known as the “Stone Age”
Between 6000 B.C and 1000 B.C they only investigated high value materials.
Discovery of copper could have been accidental but, turned out to be highly useful - in fire was made softer and more useful.
Later working with copper, about 4500 B.C - this led to creating more durable strong materials such as bronze (made when copper and tin are heated together)
1200 B.C Hittites discovered how to extract iron from rock - this was known as the Iron Age, which eventually led people to combine iron with carbon which made steel which helped them with hunting and armouring themselves.
Emerging Ideas About the Composition of Matter
Greek philosophers observed that you could break down rock particles into a powder state.
In 400 B.C the Greek philosopher Democritus used the word Atomos to describe the smallest particles that could not be further broken down. (Atomos means “Indivisible”)
Democritus stated that each type of material was made up of different types of Atomos, he believed that these particles gave each material its own set of properties.
By mixing different Atomos you could make new materials with their own unique properties, however in about 350 B.C another greek philosopher named Aristotle believed in a different hypothesis - he stated that everything was made of Earth, fire, and water because he was well known his opinion was more prefered for 2000 years.

From Alchemy to Chemistry
Experiments with matter were mainly carried out by alchemists, for the next 2000 years.
People who were part magician part scientist were known as Alchemists.
The word "Alchemy" comes the Arabic Kimiya, which translates as 'The Chemist"
Alchemists beleived that it was possible to change metal to gold and they were not interested in understanding the nature of matter.
Alchemists performed some of the very first chemistry experiments.
They invented many of the tools that are useful in labs today, such as beakers, and filters.
They discovered the plaster of Paris, which is used to hold broken bones in place whilst they heal.
New Interests in Atoms
Experiments with matter were mainly carried out by alchemists, for the next 2000 years.
Robert Boyle experimented with behaviour of gases in the 1660’s, he became convinced that matter was made up of tiny particles just like Democritus had thought in 400 B.C
Boyle believed that tiny particles existed in many different shapes and sizes, he also believed that they would form together to create individual substances. He felt that the purpose of chemistry was to determine types of particles making up each substance.
Chemistry Develops a New Science
The French scientist Antoine Laurent Lavoisier studied chemical interactions in the 1770’s.
By the late 1780’s he developed a system for naming chemicals this made it easier to compare the results of their experiments.
Hydrogen, oxygen and carbon were defined by Lavoisier’s discoveries.
How Our Understanding of Matter Has Changed Over Time
An Atomic Theory Takes Shape
In 1808 John Dalton was an english scientist who used observations from experiments to develop his own theory of composition of matter he suggested that matter was made of elements, he was the first to define an element as a pure substance which contained no other substance.
Dalton stated that each element is composed of a particle called an atom.
He put forward the first modern theory of atomic structure.
Each element is composed of a particle called an atom.
Daltons model is called the Billard Ball Model because he thought of tiny atoms as solid spheres.
Adding Electrons to The Atomic Model
Daltons work on structure of the atom was continued by British physisicst J.J Thomson - he is credited with being the first person to discover a subatomic particle (a particle which is smaller than an atom)
Dalton experimented with cathode rays and he concluded that rays are made up of streams of negatively charged particles - he showed that these particles were a lot smaller in mass than even a hydrogen atom, he named them electrons.
Alough Thomson inferred that these invisible electrons were part of atoms many peple did not agree with him in the beginning. Others believed that atoms were the smallest paricle of matter and could not be further broken down.
In 1897 Thomson proposed what is called a "Raisin Bun Model" of the atom. He described the atom as a postiviley charged sphere in wich negatively charged electrons were embedded like raisins in a bun.
A Canadian Contribution to Atomic Theory
Support for the Nagaoka Model and the idea of the central nucleus came from the British Scientist, Earnest Rutherford won a nobel prize in 1908 for work in radio activity, this work contributed to the development of his model of the atom.
Using Thomsons model Rutherford conduted experiments in which he shot positively charged particles through thin gold foil his prediction was that all the high speed particles would pass straight through the foil without being affected by the gold atoms - instead results showed that while most did behave as predicted, some were greatly deflected. To explain why this might happen Earnest proposed a new model he suggested that atoms were mainly empty space through which the postitive particles could pass but at the core was a postively tiny charged centre this he called the Nucleus.
Bohr's Model
Niels Bohr who was working with Rutherford suggested that electrons do not orbit randomly in an atom. Bohr said that they move in specific circular orbits, also known as electron shells - Niels believed that elecetrons jumped between shells gaining/losing energy.
Bohr won the Nobel Prize in Physics in 1922.
James Chadwick another British physicist discovered that the nucleus conatined postively charged particles called protons, and natural paricles called neutrons.
In modern times most people still use the Bohr model to describe the aprticles that make up the atom.
Further research in the area of quantum mechanics has found that the structure of the atom is different from Bohrs model.
The quantum mechanics model of the atom states electrons as existing in a charged cloud around the nucleus.
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