Parts of an Atom
What is an atom?
• Atoms are the fundamental building blocks of
all things
• Atoms are the most basic unit of matter
• Atoms contain three different types of
subatomic particles
Atoms are made up of protons,
neutrons, and electrons
- Protons: particles with a
positive charge; can be found
in the nucleus
- Neutrons: particles with no
charge (a neutral charge); can
be found in the nucleus
- Electrons: particles with a
negative charge that can be
found orbiting the nucleus in
the electron cloud
• The atomic number
equals the number of
protons.
• The electrons in a
neutral atom equal the
number of protons.
• The mass number
equals the sum of the
protons and neutrons.
Where are electrons found?
Electrons exist in orbitals or energy levels
2 electrons fit in the first energy level
8 electrons fit in each subsequent energy level
Helium (He)
2 neutrons
2 protons
2 electrons
Carbon (C)
6 neutrons
6 protons
6 electrons
2 in first level, 4 in second
• The charge indicates the
number of electrons that
have been lost or gained.
• A positive charge
indicates the number of
electrons (which are
negatively charged) that
have been lost.
• A negative charge
indicates the number of
electrons that have been
gained.
• This structure can be
written as part of a
chemical symbol.
A chemical element is a pure substance that consists entirely of
one type of atom. Elements are mapped on the periodic table.
Do all atoms of the same element
always have the same number of
neutrons?
Answer: NO
Atoms of the same element with differing numbers
of neutrons are called isotopes
• The combinations of
two or more
elements in definite
proportions form a
chemical compound.
• Naming compounds
(molecular formulae):
H20 = 2 parts hydrogen
to 1 part oxygen
• The physical and chemical properties of a
compound are usually very different from
those of the elements from which it is formed.
• Example:
– Sodium is a silverish metal
– Chlorine is a greenish gas
– Sodium Chloride (NaCl) is table salt
Atoms in compounds are
bonded together by chemical
bonds.
2 types: Ionic, Covalent
• Ionic bonds are formed when one or more
electrons are transferred from one atom to
another
• Example: Sodium Chloride (NaCl)
• Covalent bonds are formed when electrons
are shared between atoms
• A molecule is the structure that results when
atoms join together by covalent bonding
• Example: Water (H2O)
Van der Waals Forces
• When molecules are close together, the
oppositely charged regions are attracted to
each other.
• Van der Waals Forces are the slight forces of
attraction
• These forces explain why a gecko can climb up
vertical surfaces (suction cup like forces)