SCIE 4001
Unit 1
Introduction
About Matter
Nature of Matter
Properties of Matter
States of Matter
Kinetic Theory of Gases
 
 
 
Brownian Motion
 

Unit 1.1a - Investigating the Nature of Matter

Based on our observations so far we propose:

Hypothesis: Matter is made up of tiny building blocks called atoms...

Questions:

1. What is the nature of atoms?

2. How do these atoms behave?

While atoms are made up of smaller particles, any attempt to break them up into their component parts results in the loss of their nature...

Proof? Radioactive experiments break apart atoms and can result in new 'material'.

1a. So how many different kinds of atoms are there?

Some will say 112... but many will say 90 or 92 and even then there is a little disagreement as 2 of these are so short lived or rare (like the other 10) that the definition of naturally occurring is stretched.

But even if we take it as 90...

1b. How are atoms built up?

hydrogen
lithium
carbon
oxygen
Fig. 1-1.25 Hydrogen Atom
Fig. 1-1.26 Lithium Atom
Fig. 1-1.27 Carbon Atom
Fig. 1-1.28 Oxygen Atom

The simplest model is that atoms are made up of positively charged protons held together by uncharged neutrons in a dense space called the nucleus and around these revolve electrons. The diagram on the above (fig. 1-1.2) shows some simple elements:

— hydrogen with 1 proton and 1 electron

— lithium which has 3 protons, 3 neutrons and 3 electrons

— carbon which has 6 protons, 6 neutrons and 6 electrons and

— oxygen which has 8 protons, 8 neutrons and 8 electrons.

The number of protons is always equal to the number of neutrons so that the atom as a whole is electrically neutral.

Proof? Physicists and chemists have done investigations and even though they have refined the model, this model is sufficient for us... The proofs are way beyond this course! But recall that science is made up of a body of peer reviewed, repeatable, reliable and observable knowledge as well as an investigative process to explain the natural world... so lets accept it for now in this light...

How do we get the wide range of materials from only 90 building blocks?

Materials that are made up of a single type of atoms are called elements and when elements chemically combine they form compounds. We may have mixtures which can be both elements and compounds or elements or compounds only.

Well many types of atoms don't like to be solitary! The exceptions are the 'noble' gases (helium, neon, argon, krypton xenon, radon) making it closer to 84!... So let's look at how they combine to form molecules...

Elements — only one kind of atom

— No combination - inert gases exist as solitary atoms.

two atoms
molecule 4
molecule metal
Fig. 1-1.29 Two Similar Atoms
Fig. 1-1.30 Four Similar Atoms
Fig. 1-1.31 Group of Metal Atoms surrounded by free electronss

— Self-combination (these are pretty much elements)

— Some atoms combine in pairs e.g. hydrogen, oxygen, nitrogen; these are usually non-metals and are often gases...

— Carbon (in diamond form), silicon and a few others hang around in groups of 4...

— Most metals form a kind of pool with a large group of atoms...

Compounds — more than one kind of atoms chemically combined together. Since elements combine in definite ratios, they exist as groups of atoms.

— Atoms of one kind in chemical combination with others. When chemically combined the properties of these compounds ('new' materials) are very different from the individual elements e.g. elements hydrogen and oxygen are gases but they combine to give a liquid water whose chemical properties are vastly different.

two atoms
molecule 4
Fig. 1-1.32 Water Molecule
Fig. 1-1.33 Carbon Dioxide

— There are various ratios with 1-1 (hydrochloric acid), 2-1 (water), 3-1 (aluminum chloride), and 3-2 (aluminum oxide) and 4-1 (methane) being the common.

Carbon has its own chemistry with a tremendous range of ratios.

two atoms
molecule 4
Fig. 1-1.34 Complex Molecule
Fig. 1-1.35 Complex Molecule of carbon, hydrogen, nitrogen and oxygen

Examination of the mathematics will show there are millions if not billions of possible combinations. Some of these compounds are very familiar to us and are used to satisfy our physical needs, for example, in our food, and materials for clothes and shelter. As a matter of fact, any material we use - whether artificial or naturally occurring! Some are simple compounds like water, vinegar, alcohol, common salt; others like clothing fibres, non-metal building materials, drugs, plant and animal tissues can be very complex compounds.

Mixtures — physical combinations of elements and or compounds.

— These consist of compounds and/or elements in an uncombined form with no specific ratios. The properties are the average of the constituents. E.g. air is a mixture of nitrogen, oxygen, carbon dioxide, argon and a few other minor components.

— Homogeneous mixtures are the same throughout their bulk and are called solutions. eg salt water, air, aqueous alcohol (like rubbing alcohol), carbonated drinks.

— Heterogeneous mixtures have components whose ratios vary within the bulk of the mixture. The vast majprity of materials in this world belong to this category so materials are often refined to heterogeneous forms or to compound or elemental form for use.

What do you think will happen if the composition of raw material imputs for an industry was variable?

Consider the agregate industry. Various ratios of gravel, sand and clay mixtures occur in natural deposits. The construction industry requires different types of gravel and sand. So in the quarry the mixture is washed with water to remove the clay, and then sieved to produce the different sizes of gravel and sand for the construction industry. The heterogeneous mixture has been treated to make a more homogeneous product.

Water in rivers and lakes are heterogeneous with dissolved and undissolved materials. Water treatment plants remove impurities so that the water can attain a homogeneous standard.

 

Main Points

1. Materials are made up of

— elements which have only one kind of atoms e.g. hydrogen, copper, oxygen and chlorine. There are around 92 of these occuring naturally.

— compounds which have more than one kind of atoms chemically combined together. There are a vast number of these occuring naturally.

— mixtures which are mde up of physical combinations of elements and or compounds. These make up the vast number of naturally occuring materials.

2. An atom has

— protons and neutrons in the nucleus

— electrons around the nucleus

— the number of protons (or electrons) determines to which element this atom belongs.

3. Atoms combine chemically to form molecules.

— a molecule is a group of atoms (often of more than one kind) which are the building blocks of compounds. These behave as units in materials.

 

Questions:

What is an atom?

What is a compound?

What is a mixture?

 

Activities

make a list of the common compounds in the home. Try to identify the elements contained in these compounds.

make a list of the common mixtures in the home. Try to classify them into homogeneous or heterogeneous. Try to identify the elements and/or compounds contained in these mixtures

The following is a simulation from PhET Interactive Simulations
University of Colorado
http://phet.colorado.edu

If you have difficulty running it click here to my Q & A Page

 

In the next section we will look at how molecules behave in materials.

 

Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.