Elements, Atoms, Compounds and Molecules

BY AN HE

Elements

• A Chemical Element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus.

• The Atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons.

• Mass range: 1.67 × 10−27 to 4.52 × 10−25 kg.• Electric charge: zero (neutral), or ion charge.• Diameter range: 62 pm (He) to 520 pm (Cs) (data

page)• Components Electrons and a compact nucleus of

protons and neutrons

Atom

METALSChemical Properties

•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 electro negativities.

Physical Properties

•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).

non-metals

Chemical Properties• 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 electro

negativities.

Physical Properties• Poor conductors of heat and

electricity. • Brittle - if a solid. • No ductile. • Do not possess metallic luster. • Transparent as a thin sheet. • Solids, liquids or gases at

room temperature.

The Periodic Table

• The periodic table of the chemical elements (also, Mendeleev's table, periodic table of the elements or just periodic table) 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 to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.

The End