1Mr. Shields Regents Chemistry U03 L06

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The “Basics”If we look at a leaf macroscopically we might describe it As green, serrated edge, smooth, containing lines etc.

If we look at this leaf on smaller and even smaller scalesWe would see that it is not just leaf but is in fact composed of very tiny units, for example:

CellsDNA moleculesRNA moleculesAmino AcidsAtoms

Dec.

Size

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So what is an Atom?So what is an Atom?The smallest particle of an element that retains the properties of the element.

The smallest particle of an element that can undergo a chemical reaction

Atoms are NON-DIVISIBLE using ordinary chemical processes

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There are today 115 elements known to man. Some arepresent naturally and some are man made.

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The Periodic Table of the Elements

2 elements are Liquid

11 elements are Gases

Elements 1 – 92 can befound in nature (except 2)

Of these 92, 78% are metals

Elements 93-115 are allmanmade

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If atoms are single elements what do we have whenWe join several atoms together?

COMPOUNDS !

A Compound is defined as 2 or more different elements chemically combined in a definite ratio of atoms and mass (ex Fe2O3).

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CompoundsCompoundsProperties of compounds are differentdifferent from those of the elements from which they are formed

They are Homogeneous (we’ll discuss this later).

Can be Broken down into elements thru chemical change decomposition (ex. 2HgO 2Hg + O2)

In the Classification of Matter (which we’ll also discuss later) Elements and Compounds are known as PURE SUBSTANCES

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Law of Definite Proportions

As we’ve discussed, a compound is a substance thatcontains two or more different elements combined in a FIXED or CONSTANT COMPOSITION

The LAW OF DEFINITE PROPORTIONS states that regardless of the amount present, a compound is always Composed of the same elements in the same proportion by mass. So what does this mean? …

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Law of Definite Proportions

So, Mg = (24.3/40.3) x 100 = 60.3% by mass and O = (16.0/40.3) x 100 = 39.7% by mass

The atomic mass of Magnesium is 24.3 amuand the mass of Oxygen is 16.0 amu.

Therefore, the total mass of MgO is 40.3 amu

Every single spec in a pile of magnesium oxide (MgO) consists of many molecules. And each molecules has:

1 Mg atom and 1 O atom

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Law of Defintie ProportionsSince the % composition of MgO is approx. 60.3% Mg and 39.7% O then ...

Then In 100g of MgO I have 60.3g of Magnesium and 39.7g of Oxygen.

This could also be stated as “the percent Composition of Oxygen in MgO is always 39.7% and the % composition of Mg in MgO is always 60.3 %”

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In 200Kg of MgO there is approximately…

39.7% x 200Kg = 79.4Kg of Oxygen AND

60.3% x 200Kg = 120.6Kg of Magnesium

How many grams of Magnesium and Oxygen do

I have if I have 200Kg of MgO? (Mg=

60.3% and O=39.7%)

Now try this one!

PROBLEM:

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In 1 ton of Fe2O3 there is approximately…

Atomic mass of Fe2O3 = (55.8x2)+(16x3)= 159.6 amu

Fe = (111.6/159.6) x 100 = 69.9% of Fe2O3

69.9% of 2000lbs = 1398 lbs

How many pounds of Iron can I theoretically

Obtain from 1 ton (2000lbs) of Fe2O3 (iron ore)?

Now try this one!