Ch. 3Sec. 1

Introduction to Atoms

central core of atom

no charge

positive charge

negative charge

Helium

Electrons move within a sphere shaped region around the nucleus.

(almost 2,000)

•# of protons in atom’s nucleus

•used to identify element

Atomic mass number

•sum of protons & neutrons

isotope-

element with same # of protons & different # of neutrons

Model Brief description

Picture

Dalton model Atoms all alike

Diff. elements-diff. masses

Thomson model

Nagaoka model

Rutherford model

Bohr model

Chadwick model

Present Modern model

Were you paying

attention?

Protons, neutrons and electrons

• What are the three main particles in an atom?

proton- positive chargeneutron- no charge

electron- negative charge

• How do the particles of an atom differ in electric

charge?

Each atom has equal numbers of positively charged protons and negatively charged electrons.

• Why do atoms have no electric charge even though most of their particles have

charges?

The number of protons in each atom of that element.

• What is the atomic number of an element?

Each element has a unique atomic number because all atoms of that element have the same number of

protons.• How can atomic numbers be

used to distinguish one element from another?

Each atom of nitrogen-15 contains 7 protons, 8 neutrons and 7 electrons.

• The atomic number of the isotope nitrogen-15 is 7.

How many protons, neutrons and electrons make up an

atom of nitrogen-15?

Each atom of nitrogen-15 contains 7 protons, 8 neutrons and 7 electrons.

• The atomic number of the isotope nitrogen-15 is 7.

How many protons, neutrons and electrons make up an

atom of nitrogen-15?

Atoms are too small to be seen.

• What is the main reason that scientists use models to

study atoms?