Download ATOMS AND ELEMENTS

ATOMS AND ELEMENTS
Element
• An atom with a particular number of protons
in its nucleus
• 92 elements occur naturally on Earth and in
the stars
• About 20 more have been created in
laboratory conditions
• Organized on the Periodic Table by Atomic
Number
Atom
• Smallest part of an element that has all the
characteristics of that element
• Nucleus – center of the atom made up of protons &
neutrons
• Proton – a tiny particle in the nucleus of an atom that
has mass and a positive electrical charge
• Neutron - a tiny particle in the nucleus of an atom that
has mass (about the same as a proton) and no
electrical charge
• Electron – smaller particles surrounding the nucleus
that have little mass and a negative electrical charge
Electron Cloud
• Area around the nucleus of an atom where
electrons are found
Valence Electrons
• Electrons in the outer energy level determine
the chemical behavior of different elements
• Full outer energy level  8 electrons
• Examples:
– Sodium (Na)  1 valence electron and combines
easily
– He, Ne, Ar  8 valence electrons & do not easily
combine