A history of chemistry

“Old dead guys”

400 BC- Democritus- first to come up with the idea that things are made of “atoms”

It all started back when…

1803- John Dalton Proposed the atomic theory

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1869- Dmitri Mendeleev Arranged elements into 7 groups with

similar properties… 1st version of periodic table.

Next was

Discovered electrons and isotopes

1897- JJ Thomson

Famous experiment determined the charge of an electron… which is??

1909 Millikan

Established that the nucleus of an atom was very dense and positively charged while electrons were outside the nucleus

1911 Rutherford

Made a model of the atom where electrons were in different orbitals

1922 Niels Bohr

Discovery of the neutron

1932 Chadwick

First of all… Elements are substances that cannot be broken down into simpler parts

Elements are made of atoms.. .Carbon is made of carbon atoms etc.

How small is an atom??? We can break down an atom but it loses its

properties when we do…

Moving on to atomic structure

Three types of particles Electrons Protons Neutrons

Atoms are made of…

Very tiny Mass is basically zero (m=0) Negative charge (-1) Located flying around the nucleus

Electrons

Very large compared to electrons (mass =1) Positive charge (+1) Located in the nucleus of an atom

Protons

Large like protons (mass=1) Neutral charge or no charge Located in the nucleus

Neutrons

If this were the size of hydrogen nucleus, the electron would be spinning about a quarter mile away….

In a neutral atom, protons always equal electrons

Hydrogen has… 1 proton… 1 electron Helium has… 2 protons… 2 electrons

Atomic number = number of protons in nucleus

Atomic Mass= how many protons AND neurtons

How many protons in H? How many neutron in H How many electrons?

How many P? N? E?

Let’s try another

P? N? E?

Hydrogen:

Helium:

Bohr Models

Boron

Neon (noble gas)

More Bohr Models

Magnesium

Last one