BBC Bitesize KS3 Elements, Compounds & Mixtures

Atoms , Molecules - Basics - Animated lesson in video

Elements,Compounds and Mixtures

elements - only contain one type of atom and the list of elements is the periodic table

compounds - a mix of two or more atoms
Mixture - combination of two or more compound/molecule

Atoms

The atom is a basic unit of matter that consists 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 (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other by chemical bonds based on the same force, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it is positively or negatively charged and is known as an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.

^{To read more please visit http://en.wikipedia.org/wiki/Atom .}

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The difference between metals and non-metals

Chemical Properties

Metals

• Usually have 1-3 electrons in their outer shell.
• Lose their valence electrons easily.
• Form oxides that are basic.
• Are good reducing agents.
• Have lower electronegativities.

Nonmetals

• Usually have 4-8 electrons in their outer shell.
• Gain or share valence electrons easily.
• Form oxides that are acidic.
• Are good oxidizing agents.
• Have higher electronegativities.

Physical Properties

Metals

• Good electrical conductors and heat conductors.
• Malleable - can be beaten into thin sheets.
• Ductile - can be stretched into wire.
• Possess metallic luster.
• Opaque as thin sheet.
• Solid at room temperature (except Hg).

Nonmetals

• Poor conductors of heat and electricity.
• Brittle - if a solid.
• Nonductile.
• Do not possess metallic luster.
• Transparent as a thin sheet.
• Solids, liquids or gases at room temperature.