Elements, Compounds and Mixtures

Elements, compounds and mixtures are some categories that refer to the composition of a substance. The properties of substances allow scientists to identify a given substance as an element, compound or mixture.

Elements
An element is a substance that cannot be further broken down using chemical reactions to give simpler substances. For example, when common salt is heated and then electrically decomposed, it gives sodium and chlorine which cannot be further broken down into simpler substances. Hence, common salt is a compound while sodium and chlorine are elements.
An element has both a name and a symbol for it to be represented in the periodic table. For instance, an element may be named "hydrogen" and designated the symbol "H".
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An element is either made up of atoms or molecules. A molecule is a group of two or more atoms chemically joined together.

 

So, how do you classify elements?

 

1. Classification by state.

Elements can be classified according to their physical state at room temperature and pressure.

2. Classification as metals/metalloids/non-metals

Elements can also be classified by their metallic properties. Elements that are good conductors of electricity would be classified under metals while elements that are poor conductors of electricity would be classified under non-metals. However, there are some elements that have both metallic and non-metallic properties, which are classified under metalloids.

3. Periodic table classification

Elements belonging to the same column, or group, (vertical) have similar chemical properties while elements in the same row, or period, (horizontal) show a gradual decrease in non-metallic properties.

 

Compounds

A compound is a substance containing 2 or more elements chemically joined together. It can be decomposed to give 2 or more simpler substances. A compound is formed through chemical reaction between different elements. Usually, compounds can be broken back down into their constituent elements by using electricity or heat.

 

Mixtures

A mixture comprises 2 or more substances that are not bonded together through chemical means. It can comprise of elements, compounds or both, and these may be solids, liquids or gases.

 

Differences between a compound and a mixture

1. A compound's melting and boiling points are fixed, while a mixture melts and boils over different temperatures.

2. A compound requires chemical reactions to be separated into its constituent elements while a mixture may be easily separated into its components using physical means.

 

Periodic table

The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic numbers, electron configurations (electron shell model), and recurring chemical properties. Elements are presented in order of increasing atomic number (the number of protons in the nucleus). The standard form of the table consists of a grid of elements laid out in 18 columns and 7 rows, with a double row of elements below that. The table can also be deconstructed into four rectangular blocks: the s-block to the left, the p-block to the right, the d-block in the middle, and the f-block below that.
The rows of the table are called periods; the columns are called groups, with some of these having names such as halogens or noble gases. Since, by definition, a periodic table incorporates recurring trends, any such table can be used to derive relationships between the properties of the elements and predict the properties of new, yet to be discovered or synthesized, elements. As a result, a periodic table—whether in the standard form or some other variant—provides a useful framework for analyzing chemical behavior, and such tables are widely used in chemistry and other sciences.
In the standard periodic table, the elements are listed in order of increasing atomic number (the number of protons in the nucleus of an atom). A new row (period) is started when a new electron shell has its first electron. Columns (groups) are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. oxygen and selenium are in the same column because they both have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.

The information above is found on Wikipedia

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