Matter is composed of basic building blocks called atoms. Atoms were originally thought to be indivisible spheres, but are now understood to have internal structure. Atoms contain a tiny, dense nucleus of protons and neutrons surrounded by electrons. The number of protons determines the element, while neutrons and electrons can vary between atoms of the same element. Most atoms are electrically neutral, but can become ions by gaining or losing electrons.

1. But, what is matter made of?

2. Long time ago, Greeks
wonder about matter
composition. As a rock
breaks into smaller
fragments, what would be
the smallest fragment
achievable?
To these early Greeks,
matter could not be
continuously broken down
and divided indefinitely.

3. Rather, there was a basic unit or building block
that was indivisible and foundational to its
structure.
Atomos in
Greek means
indivisible.

4. An atom is a
fundamental piece of
matter.
All matter is made up
of this.
A lithium atom.

5. An average measurement of an atom size has
been stimated.
For example, the smallest
atom that exists, is
HYDROGEN.
Hydrogen size = 0’000 000 000 1 m

6.  Atoms were thought as spheres of matter.
Littles pieces of a bigger body.
 But there were several problems with this
model… Electric phenomena was not
explainable.

7. To explain attraction and repulsion between
bodies, scienctists resort to electric charge, a
property of matter.
◦ Electric charge causes electric phenomena:
attraction and repulsion.
◦ There are two different types of electric charge:
positive and negative.

8. Think about magnets. And wait.

9.  https://www.youtube.com/watch?v=-
4Us5PTb4J8

10. The simplest atom is made up of three main
particles:
◦ Proton positively charged.
◦ Neutron no charge.
◦ Electron: negative charge.
They are organized in
◦ A nucleus: protons (+) and neutrons.(0)
◦ Electrons (-) around the nucleus.

11. Subatomic
particle
Proton Neutron Electron
Charge + 0 -
Mass
±hydrogen atom
mass
± proton mass
±hydrogen
mass x 2.10-3
Where are they? Nucleus Nucleus Around nucleus
There is nothing but empty space between the
nucleus and electrons.

13. Matter that surrounds us is, in general, neutral
(we don’t get a discharge every single time
we touch something).
So, a neutral atom must have
positive charges = negative charges
In other words,
number of protons = number of electrons

14. ¡BUT! Sometimes atoms
are charged.
Because of proximity of other atoms or
other circumstances, like electric
discharges, high temperatures…

15.  Atoms like to be stable. They feel most stable when
their outer electron shells are full. They become full
when they have eight electrons in them.
 This is called the octet rule.
 They get eight electrons by either borrowing some
from or giving some to another atom

16.  An ion is an atom that has gained or lost one
or more electrons and therefore has a
negative or positive charge.
◦ A cation is an atom that has lost an electron and
therefore has more positive protons than negative
electrons, so it is positively charged.
◦ An anion is an atom that has gained an electron and
is negatively charged.

17. 5

18.  A chemical element represents all the atoms
of the same type in nature. An element is
a substance consisting of atoms which all
have the same number of protons.

20. Although an element's atoms must all have the
same number of protons, they can have
different numbers of neutrons and hence
different masses.

21. When atoms of
the same
element have
different
numbers of
neutrons, they
are
called isotopes.

22. Pure
substances
Simple
substances
Atoms (noble
gases)
Molecules
(oxigen,
nitrogen)
Otrher clusters
(metals,
graphite)
Compounds
Molecules
(water)
Ionic crystals
(cooking salt)
Same
element
Different
elements
He

23.  http://www.nyu.edu/pages/mathmol/textbook/at
 http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-
matter/the-nuclei-of-atoms-at-the-heart-of-matter/oms.html
 http://education-portal.com/academy/lesson/ions-predicting-formation-charge-and-
formulas-of-ions.html
 http://www.wikihow.com/Find-Electrons
 https://www.physicsforums.com/threads/whats-inbetween-an-atoms-nucleus-and-
electrons.230889/
 http://chemwiki.ucdavis.edu/Physical_Chemistry/Atomic_Theory/Atomic_Theory
Just for educational purpose.