ATOMS Chapter 4

What is an Atom? The smallest particle into which an element can be divided and still be the same substance The building blocks of all matter

Size of Atoms Atoms are really, really small Even the biggest atoms can’t be seen

Can you cut it? Cut a strip of paper 28 cm long by 4 cm wide If you can cut the strip of paper in half 31 times you will end up with a piece of paper the size of an atom. Take your strip of paper and cut it into equal halves. Cut one of the remaining pieces of paper into equal halves. Continue to cut the strip into equal halves as many times as you can. Make all cuts parallel to the first one. When the width gets longer than the length, you may cut off the excess, but that does not count as a cut.

How far did you get? Here are some comparisons to think about!  Cut cm Child's hand  Cut cm Fingers, ears, toes  Cut cm Watch, mushroom, eye  Cut cm Rings, insects  Cut 6.44 cm Poppy seeds  Cut 8 1 mm Thread. Congratulations if your still in!  Cut mm Still cutting? Most have quit by now  Cut mm Microscopic range, human hair  Cut mm Width of paper, microchip components  Cut 18 1 micron Water purification openings, bacteria  Cut 19.5 micron Visible light waves  Cut micron Electron microscope range  Cut micron The size of an Atom!

Is there anything smaller than an atom? YES

Parts of an Atom Three subatomic particles (there are more) - protons – positive charge, located in the nucleus - neutrons – no charge, located in the nucleus - electrons – negative charge, located in the electron cloud

Charged Atoms When an atom has the same number of protons and electrons, the atom is neutral When there is a different number of protons and electrons, the atom has a charge Charged atoms are called ions

An ion is positive when the protons outnumber the electrons An ion is negative when the electrons outnumber the protons

Isotopes Atoms of an element that have the same number of protons but different number of neutrons

Do Section Review Page 89

Electron Shells 1 st shell can hold 2 2 nd shell can hold 8 3 rd shell can hold 18 but for our purposes we will consider it full at 8

Bohr Models

Do Bohr Model activity sheet

Forces Gravity – attraction between particles in the atom. Very small force in the atom Electromagnetic – holds electrons around the nucleus Strong – holds the nucleus together (is stronger than the electromagnetic force that is pulling it apart Weak – responsible for radioactivity. Helps change neutrons into protons and electrons