THE A

TOM

HOW SMALL IS AN ATOM?

Think of a penny…• A penny contains about 2 x 1022

atoms of copper and zinc• Aluminum has average sized atoms

diameter of .00000003 cm• Aluminum foil is 50,000 atoms thick!

WHAT IS AN ATOM MADE OF?Nucleus small, positively charged center of an atom that

consists of protons and neutrons Contains most of atom’s mass Diameter is 1/100,000 the diameter of the atomProtons positive charged subatomic particle with an electrical charge of 1+Neutrons neutrally charged subatomic particles that do not have an electrical charge Electrons negatively charged subatomic particles with an electrical charge of 1- that are found in the electric cloud

KrogerCoke

ATOMIC MASS UNIT

• Def. a unit of mass that describes the mass of an atom

• SI unit for mass of particles

• Carbon-12 is used by scientists to determine an atomic mass unit .

• The amu is exactly 1/12 the mass of a carbon-12 atom.

• Because carbon-12 has six protons and six neutrons in its nucleus, the mass of a proton and the mass of a neutron are each considered to be 1 amu.

HOW DO ATOMS OF DIFFERENT ELEMENTS DIFFER?

By the number of protons, neutrons, and electrons!

Atomic number= (Z) number of protons in the nucleus of a given atom

Q. What is the atomic number for …

Nitrogen

A.7

Lead

A. 82

MASS NUMBER

• Def. (A) total number of neutrons and protons in the nucleus of an atom

• Electrons are not included bc their mass is so small that they have little effect on the atom’s mass