Download Atom Notes - mcewenscience

8th Grade Science
Chemistry Concepts
Atoms
Objectives
1. Compare the charge, location and
relative mass of protons, neutrons, and
electrons.
2. Calculate the number of particles in an
atom using the atomic number, mass
number, and overall charge.
3. Calculate the atomic mass of elements.
All substances are composed of elements
Elements are pure substances that cannot
be broken down into simpler chemical
substances.
What’s the Matter?
• The smallest particle that an element can
be broken down into and still be that
element is called an atom.
• Atoms are the building blocks of all matter.
– Matter is anything that has mass and volume
• Atoms cannot be seen – even with a
microscope! They average about
300/1,000,000 cm in diameter.
• It would take 50,000 aluminum atoms to
equal the thickness of sheet of foil!
Atomic Structure
• An atom has a small positively charged
center surrounded by a large region with
negatively charged particles
Atomic Structure
• An atom is made up of three main
smaller particles called subatomic
particles.
• These are protons, neutrons, and
electrons.
• Each of these has a specific location,
charge and mass
Atomic Structure
• The center of an atom
is called the nucleus.
• Inside the nucleus are
two types of subatomic
particles: protons and
neutrons.
• The nucleus makes up
99% of an atoms mass
• 1/100,000 the diameter
of the atom
nucleus
P For Positive!
• Protons are positively charged particles in
the nucleus.
• All protons are identical to each other.
• Mass of a proton = 1.7 x 10-24g = 1 atomic
mass unit (amu)
• Made of three smaller particles called
quarks.
N Is For Neutral!
• Neutrons are particles in the nucleus of
an atom that have no charge (neutral)
• All neutrons are identical.
• Mass of a neutron = 1 amu
• Made of three smaller particles called
quarks.
E is for Electron!
• Outside the nucleus are negatively
charged particles called electrons.
• They are found in regions called electron
clouds.
• They orbit the nucleus, but not in definite
paths.
• Mass is so small it is considered zero
Nucleus
contains
Protons
-positive
p+
Electrons
-carry a negative charge
e-
Neutrons
-neutral
n0
Electrons, Protons, & Neutrons:
Why are they important?
• The number of protons in an atom tells you
what element it is: carbon, silicon, etc.
• The number of protons an element has is
called the atomic number.
• Every element has a unique number of
protons.
1 proton  Hydrogen H
6 protons  Carbon C
7 protons  Nitrogen N
8 protons  Oxygen O
Electrons, Protons, & Neutrons:
Why are they important?
• Atoms of the same
element (same number
of protons) may have
different numbers of
neutrons.
• These atoms are known
as isotopes, and share
similar chemical and
physical properties
• There are at least 2760
naturally occurring
isotopes; tin has 38!
Electrons, Protons, & Neutrons:
Why are they important?
• The neutrons and protons make up
most of the mass of an atom. This
combined mass is called the mass
number.
• The average of the masses of all
naturally occurring isotopes is called the
atomic mass.
Electrons, Protons, & Neutrons:
Why are they important?
• The number of electrons in an atom is
equal to the number of protons.
• Therefore, overall atoms have no net
charge – they are neutral.
• An atom that is not neutral is called an
ion.
– Positive ion (cation) = more protons than
electrons
– Negative ion (anion) = more electrons than
protons
Let the force be with you!
• Objects that have the same charge repel
each other, while objects with opposite
charges attract each other.
• This is due to the electromagnetic force.
• The electromagnetic force keeps electrons
around the nucleus because they are
attracted to the protons (opposites attract!)
• The strong force overcomes the
electromagnetic force and keeps protons
in the nucleus close together.