Elements compounds and mixtures

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A sample of chlorine atoms (Cl). All atoms in the sample consist of chlorine, so the substance is homogeneous.

منگل، 18 ذو القعد، 1436

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Elements

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منگل، 18 ذو القعد، 1436

The earth’s crust consists of 5 main elements.

The human body consists mostly of 3 main elements.

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Classification of Elements as Metals & Non- Metals

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منگل، 18 ذو القعد، 1436

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Elements & symbols

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* Physical states are given at room temperature.

METALS

NON- METALS

منگل، 18 ذو القعد، 1436

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Compounds

Most elements react to form compounds.

Example, H2O

The proportions of elements in compounds are the same irrespective of how the compound was formed.

The composition of a pure compound is always the same.

If water is decomposed, then there will always be twice as much hydrogen gas formed as oxygen gas.

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منگل، 18 ذو القعد، 1436

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Characteristics of compound

It is a pure substance.

It is always homogenous

Represented by a FORMULA, eg sodium chloride NaCl, methane CH4 and glucose C6H12O6

There must be at least two different types of atom (elements) in a compound.

Have a fixed composition and therefore a fixed ratio of atoms represented by a fixed formula.

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منگل، 18 ذو القعد، 1436

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CHARACTERISTICS OF COMPOUND

Elements are not easily separated by physical means.

The compound has properties quite different from the elements it is formed from.

The formula of a compound summarizes the 'whole number' atomic ratio of what it is made up of eg methane CH4 is composed of 1 carbon atom combined with 4 hydrogen atoms.

The word formula can also apply to elements. eg hydrogen H2, oxygen O2, ozone O3, phosphorus P4.

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منگل، 18 ذو القعد، 1436

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Compounds