Introduction to Atoms

Vocabulary• Atom-

• Sub-atomic Particles-

• Nucleus-

• Atomic Models-

What is an atom?In this section I want you too…

• Know a general idea of the different models of the atoms, and why the models have changed over time

• Know what Sub-Atomic Particle each model helped to explain about an atom

• Be able to draw and label sub-atomic particles and the atom as we understand it today

Matter may consist of elements, compounds, or mixtures.

Almost all things are MATTER

All matter is made of ATOMS

Atoms are too small to see

This is an image of silicon atoms arranged on a face of a crystal. It is impossible to "see" atoms this way using ordinary light. The image was made by a Scanning Tunneling Microscope, a device that "feels" the cloud of electrons that form the outer surface of atoms, rather as a phonograph needle feels the grooves in a record.

Structure of an atom

Atomic Theory Timeline

Democritus vs. Aristotle!

Democritus – 400 BC• Coined Atoms• (ATOMOS = indivisible)• Void space• Solid, card balls• Smallest piece of matter

Aristotle – 350 BC• Continuously divisible

• Everything was apart of an “elemental”

• More of an alchemist view

1808 John DaltonDalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces.

1897: J.J. ThompsonThomson suggested that atoms had negatively charged electrons embedded in a positive sphere.•Discovered sub-atomic particle called the electron, Negatively charged particle. •How discovered?

– Using the cathode ray experiment

“Plumb Putting” Model

Rutherford was surprised that a few particles were deflected strongly. This led him to propose an atomic model with a positively charged nucleus.•Model points

– Discovered nucleus– Discovered protons– Helped to solve the mystery of the charge of the atom, but not the mass

•How discovered?– Gold Foil Expirement

1911: Ernest Rutherford

1913: Niels Bohr

Through the first part of the twentieth century, atomic models continued to change. Model points

• Specific orbits around nucleus• Electrons travel in certain successively larger orbits• Outer orbits hold more electrons• Electrons can jump orbits and on way back down,

emit light

Modern Day

Wave Mechanical Model

Summary of BIG IDEAS

• All objects that have mass and take up space are made of matter

• All matter is made of atoms• Atoms are made up of positively charged protons and

neutrally charged neutrons. Protons and neutrons stick together in the nucleus (center) of the atom

• Negatively charged electrons occupy the space around the nucleus. Electrons move so fast in this space that they resemble a cloud.

• The space between the nucleus and the electron cloud is mostly empty

• The model of the atom (what scientists think the atom looks like) has changed over time because better technology has allowed us to make better observations

Vocabulary• Atom-

• Sub-atomic Particles-

• Nucleus-

• Atomic Models-

What is an atom?In this section I want you too…

Know a general idea of the different models of the atoms, and why the models have changed over time

Know what Sub-Atomic Particle each model helped to explain about an atom

Be able to draw and label sub-atomic particles and the atom as we understand it today