Structure of the Atom

Structure of the Atom

by Hannah Freeman

​The Periodic Table

​In this unit we will be learning about the elements on the periodic table.  In order to do this, it is essential we understand atomic structure first.

​The Atom

​Atom: the smallest particle of an element that still has the properties of that element.

Remember: An element is the simplest form of matter

Ex. Water (H2O) is made of 2 atoms of the element hydrogen (H) and 1 atom of the element oxygen (O)

Multiple Choice

If NaCl is table salt then that means there are how many atoms of each element?

• 1

• 2

• 3

• 4

​The Discovery of Atomic Structure

​400 BC – Democritus

First to name the atom

Atomus means indivisible in Greek and he thought there was nothing smaller than an atom.

​

1803 – John Dalton’s Solid Sphere model

Atom is a solid sphere that can’t get any smaller

​

1869 – Dmitri Mendeleev

Developed the first periodic table of elements, organized by atomic mass

​The Discovery of Atomic Structure

​1913 – Henry Moseley

Discovered the number of protons is unique to each element (atomic number) and arranged the Periodic Table this way

1913 – Niels Bohr Bohr Model

Electrons are negative particles that travel in fixed orbits around the positively charged nucleus

1926 – Schrodinger and Heisenberg Electron Cloud model

The nucleus is surrounded by an electron cloud that is divided into shells, but electrons do not travel in fixed orbit

​The Discovery of Atomic Structure

​1904 – JJ Thomson Plum Pudding Model

The atom is divisible- a positively charged sphere with negative particles embedded throughout

​

1911 – Ernest Rutherford Nuclear Model

Gold foil experiment

Nucleus=heavier mass w/ positive charged particles and

Surrounding area=less heavy negative charged particles

​Summary of the Structure

​Two parts to the atom:

Nucleus

• Dense center with most of the mass

• Made of protons and neutrons

• Positively charged

​

Electron cloud = Space surrounding the nucleus

• Broken down into regions of space called “shells” or “energy levels”

• Electrons in shells further from the nucleus have the most energy

• Electrons in the outermost energy level are called valence electrons

• Negatively charged

​

Multiple Choice

True or false: The nucleus is the negatively charged region of the atom

• True

• False

​Subatomic Particles

​Proton: (p+) positive particle in the nucleus

​

Neutron: (n0) neutral particle in the nucleus with protons

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Electron: (e-) negative particle outside of the nucleus in the electron cloud

Open Ended

What do we know about positive and negative charges?

​What holds it together?

​Forces:

Attractive force between the (+) nucleus and (–) electron cloud

Remember opposite electrical charges attract

This is what holds the atom together

Repulsive force between (–) electrons

Electrons want to be as far apart from each other as possible

What gives the electron cloud volume

Repulsive force between (+) protons

Protons want to be as far apart from each other as possible

An insane amount of energy holds the nucleus together because of this