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Section 1: Introduction to Atoms

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1 Section 1: Introduction to Atoms
How did atomic theory develop and change? What is the modern model of the atom?

2 How is the periodic table organized?
Imagine you have a piece of aluminum foil, and you cut it in half. If each of these pieces is cut in half a second, third, and fourth time, the pieces become smaller but are still aluminum. How small must a piece be so that at the next cut it will no longer be aluminum?

3 Atomic Theory and Models
Dalton thought that atoms were like smooth, hard spheres that could not be broken into smaller pieces.

4 Modern Model of an Atom This model of a carbon atom consists of positively charged protons and neutral neutrons in a nucleus that is surrounded by a cloud of negatively charged electrons.

5 Modern Model of an Atom This model of an atom shows electrons in a frozen position that can be used to learn about chemistry. The nucleus contains protons and neutrons that make up the mass of the atom. The tiny electrons are arranged in different energy levels around the nucleus. 5

6 Particles in an Atom An atom is composed of positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are about equal in mass. An electron has about 1/2,000 the mass of a proton or neutron.

7 Identifies the name of the element
Atomic Number # protons Top # in Periodic Table Identifies the name of the element Example: # protons (+) = 6 Atomic # = 6 Element Name: Carbon 7

8 Isotopes & Mass Number Isotopes are atoms with the same number of protons and electrons but differerent number of neutrons. Mass number = total particles in the nucleus (protons + neutrons)

9 End of Section: Introduction to Atoms

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