Defining the Atom

Page
2

He calculated the mass of the electron; that is very similar to the excepted mass given today.

Slide 9

Protons

Eugen Goldstein (1850-1930) observed in 1886 that in a cathode-ray tube there were rays going in the opposite direction. He concluded they were positively charged particles.

Protons are positively charged subatomic particles.

Each proton has a mass about 1840 times that of an electron.

Slide 10

Neutrons

In 1932 English physicist James Chadwick (1891-1974) confirmed the existence of another subatomic particle.

Neutrons are subatomic particles with no charge but a mass nearly equal to the proton.

Slide 11

Rutherford’s Gold-Foil Experiment

This experiment change the prevailing thought of the structure of the atom.

Because of this experiment Rutherford concluded that most the of alpha particles pass through b/c the atom is mostly empty space, and the reason that some of the particles were deflected were due to the concentration of the positive charge in the atom which is now known as the nucleus.

Slide 12

Structure of the atom

The nucleus of the atom is the tiny central core of an atom and is composed of protons and neutrons.

Rutherford’s model is the nuclear atom: In the nuclear atom, the proton and neutron are located in the nucleus. The electrons are distributed around the nucleus.

This will later be revised, let’s sneak peak @ page 128.

Slide 13

Distinguishing Among Atoms

We learned yesterday that atoms are composed of protons, neutrons, and electrons.

Protons and Neutrons are in the nucleus and electrons surround the nucleus.

So how do elements differ if they all contain atoms?

Slide 14

Atomic Number

Elements are different because they contain different numbers of protons.

The atomic number of an element is the number of protons in the nucleus of an atom in that element.

Ex: The atomic number of Hydrogen (H) is 1, so all hydrogen atoms have 1 proton.

Ex: All Oxygen atoms (O) have 8 protons, so the atomic number of Oxygen is 8.

Slide 15

Atomic Number

Remember all atoms are electrically neutral.

Therefore; the number of Protons equal the number of Electrons.

Meaning the number of negatively charged particles must equal the number of postively charged particles.