Nature of Matter
Matter
• Anything that takes up space
• Has mass
• You are made up of matter…and so is
everything around you 
Looking more closely at matter…
• Atoms: basic building
blocks of matter
• Atoms are made up of
Subatomic particles:
PROTONS
NEUTRONS
ELECTRONS
Subatomic particles
• Proton: +, nucleus
• Neutrons: neutral,
nucleus
• Electrons: negative,
cloud around nucleus;
organization inside
cloud – into shells
Atomic Rules
• The number of protons and electrons are
usually equal in an atom
• So the positives and negatives balance out…
• So the overall charge of an atom is:
0
Elements
• Pure substance
• Made up of only one type of atom
WHICH ELEMENTS ARE THE MOST
COMMON IN LIVING THINGS?
To answer that question…
• We have to look at the substances that make
up you.
• More often than not, elements do not exist in
their solitary state.
Sooo……
WHICH ELEMENTS ARE THE MOST
COMMON IN LIVING THINGS?
Key elements for living things
•
•
•
•
•
•
CARBON (C)
HYDROGEN (H)
OXYGEN (O)
PHOSPHORUS (P)
NITROGEN (N)
SULFUR (S)
Atomic Number
• Number of protons in an atom
– Carbon’s atomic number = 6
– So carbon has 6 protons
• And by default…since atoms are neutral, we
can say:
– Atomic number is also equal to the number of
electrons
PRACTICE!
• Neon = atomic number is 10
– # protons?
– # electrons?
• CHLORINE = atomic number is 17
– # protons?
– # electrons?
Side Note
• If we change the atomic number, we change
the element we are talking about…
Ions
• An atom that has gained or lost electrons
– If an atom gains electrons…it’s charge is
– If an atom loses electrons…it’s charge is
How are ions important to you?
What about the neutrons?
• Atomic Mass: sum of the protons and
neutrons in the nucleus of an atom
So…
• To figure out the number of neutrons in an
atom…you have to:
Atomic mass – atomic number = # of neutrons
Practice: carbon’s atomic number is 6, mass is
12
More practice
• Chlorine: atomic number = 17
atomic mass = 35
Isotopes
• Atoms of the same element can have different
numbers of neutrons
• Isotopes: atoms of the same element that
have different numbers of neutrons
How are isotopes important to you?
• Can be used as “chemical tracers” to help
locate certain substances at the cellular level
• Radioactive isotopes:
– Dating
– Study biological processes
– Treatments
– Exposure
Compounds
• Substance formed by the chemical
combination of two or more elements in
definite proportions
• Example: WATER!
• Water is NOT an element! Made up of 2
elements!!