Atomic structure Gr.7

1. ATOMS
The building unit of the universe!

2. Democritus
460-370 BC
A Greek philosopher
The first to suggest the idea of
atoms.
(atomos in Greek= indivisible)
Unlike other philosophers of his
time that believed that all matter
could be reduced to a
combination of four elements:
earth, water air and fire.

3. 19th century
• Elements are made up of
atoms. An atom is the
smallest part of an element
that can exist.
• Atoms of different elements
have different structure,
which is the reason why the
different elements have
different properties.
Experiments
by John
Dalton and
other
scientists
helped us to
understand
more the
nature and
structure of
atoms.

4. Atomic structure

5. • Atoms are made of smaller particles found in the center –
nucleus - that contains protons and neutrons, and other
smaller particles called electrons moving around the
nucleus in circles.
• A Proton is positively charged particles that have a
relative mass of 1.
• Neutrons are neutral (have no charge) have mass of 1.
• Atomic mass of an element is the total mass of protons
and neutrons.
• Electrons are negatively charged particles that move
around the nucleus constantly. Around 1850 electrons
together will have the same mass of a proton, we usually
neglect the mass of electrons when measuring the atomic
mass.

6. Information found in the periodic table
Atomic number
Number of protons in
the atom
Chemical
symbol
Consists of one or two
letters first is capital.
Element name
Atomic mass
Mass of nucleus
(protons + neutrons)

7. Atomic mass & atomic number
• Atomic number = protons
• Atomic mass = protons + neutrons
• Open p. 154 and use the periodic table, to find the
number of protons, electrons and neutrons in these
elements:
• Be, Cr, Al, Sc, Se, He, F, O, C, Au, Na, Ca, Ne, Si

8. Can you tell
which
element this
atom is?

9. Electronic configuration
• When electrons move around the
nucleus they do so at specific distances
from the nucleus, we call them orbits or
energy levels.
• As the electrons fill up the energy levels
they begin with the closest to the
nucleus.
• You need to remember that the first
energy level takes 2 electrons, the
second takes 8 & the third takes 8.
• For example, the electronic configuration
of sodium is 2, 8, 1.