chemical Reactions DS

Elements, Atoms, Compounds and Molecules

By Darcy p. Simonsen

Element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number.

Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, nitrogen, and oxygen. In total, 117 elements have been observed as of 2008, of which 94 occur naturally on Earth

Atom

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.

metals

a metal is an element, compound, or alloy characterized by high electrical conductivity . In a metal, atoms readily lose electrons to form positive ions; those ions are surrounded by delocalized electrons, which are responsible for the conductivity.

Non metals

non-metal is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a nonmetal.

Periodic table

The periodiс table of the chemical elements is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended

the table

Compounds

A chemical compound is a pure chemical substance consisting of two or more differen t chemical elements that can be separated into simpler substances by chemical reactions and that have a unique and defined chemical structure.

Chemical reactions

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. There are three things that speed up chemical reactions one of them are:

chemical and physical changes

1. A physical change is reversible, a chemical change is not. For example, the freezing of water would be a physical change because it can be reversed, whereas the burning of wood is a chemical change - you can't 'unburn' it.

Identifying chemical reactions There are three types of chemical

reactions, here are two: Synthesis A synthesis reaction is when there is a

combination of two or more substances and a compound results. An example A + B --> AB

Decomposition Decomposition is roughly the opposite of

synthesis it is a breaking down of one molecule into two (or more) smaller molecules or elements.

Sample decomposition reactions could include:

2 H2O + electricity -> 2 H2 + O2

make a reaction faster

use a catalystbreaking a solid into something smaller

(to increase its surface area) make the solution more concentrated,

increase the temperature.

Bibliography

Wikipedia the free encyclopaedia Google images What is the difference between a

physical change and a chemical ...