Resources for elementary and middle school science educators.

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Atomic Structure

Aim for success, not perfection.
Never give up your right to be wrong,
because then you will lose the ability to learn
new things and move forward with your life.

Dr. David M. Burns

The Structure of Matter

Definition to know : Matter is anything that has mass and takes up space (has volume).

The Modern Atomic Model

• Electrons have characteristics that are similar to waves and particles
• Their energy levels are not defined, planet-like orbits around the nucleus
• It seems most likely that electrons move in what is called the atom's electron cloud
• A spherical cloud of varying density surrounding the nucleus
• Varying density shows where an electron is more or less likely to be
• Atoms with electrons in higher energy levels have additional electron clouds of different shapes that also show where those electrons are likely to be

Parts of the Atom

Electrons

• Lightweight ( one million millionth of the mass of a speck of dust)
• Negative charge
• Surround the nucleus of an atom
• Always moving
• Can move in any direction within their shell or orbital
• Is equal to the number of protons

Protons

• Found in the nucleus
• Positive charge
• Mass is 1,836 times the mass of the electron and slightly less than the mass of the neutron
• Identifies the atomic number
• Made up of smaller particles called quarks

Neutrons

• Found in the nucleus
• Has no electric charge
• Mass is nearly 1,840 times that of the electron
• Made up of smaller particles called quarks

Mass Number

The total number of protons and neutrons in a nucleus

Atomic Number

The number of protons in an atom's nucleus

Atomic Weight

The average mass of naturally occurring isotopes of an atom.