Grade 9 Academic Science – Physics (Electricity)
Electric Charges
Section 11.1 Pages 465-471
Everything is made of matter AND all matter is made of atoms. Atoms consist of three subatomic
particles: protons, electrons and neutrons. Our ideas about the model of the atom note that
protons and neutrons are located in the nucleus (i.e., centre) of the atom while the electrons are
found in energy shells or orbits surrounding the nucleus. The electrons move in space in the
shells. Importantly, electrons can be added or removed from the atom.
Table 1. Properties of the Sub-atomic Particles of the Atom
Particle
Charge
Location
Symbol
Proton
+
Nucleus
p+
Neutron
-
Nucleus
n0
Electron
0
Outside nucleus
e-
NOTE: An element is a specific kind of atom. An element is a material that cannot be
“decomposed or broken apart” by existing means. Recall from the Space Unit, elements
are made in exploding stars (i.e., supernova) under intense heat and pressure, AND all
the “naturally occurring” elements in the Universe came from primordial elemental
hydrogen. Next, two or more elements bonded together form a molecule or, more
familiar, a compound (e.g., H2O, CH3CH2OH).
RECALL FROM EARLIER CONVERSATIONS ABOUT CHEMISTRY
 A neutrally-charged element has the same number of protons and electrons. Explain
why?
 If the number of protons and electrons in an atom are not equal, the atom has an electric
charge. It can be positive or negative. Using Table 1, how can an atom have a positive
charge? What configurations of protons and electrons would create a negative-charged
atom?
 Protons occur in the nucleus, and as such, the number of protons does not change. On
the other hand, electrons occur outside the nucleus. Moreover, electrons are in constant
motion (i.e., they move). Thus, the number of electrons can increase or decrease. How
might an atom increase its number of electrons?
Electric Force: The force of attraction or repulsion between charged objects. The force exerted
by an object with an electric charge (attraction or repulsion)
The Law of Electric Charges states that like charges repel and opposite charges attract.
With that information, use “+” and “-“ symbols to complete the following information
Repulsion
Attraction
NOTE: Closer together = Stronger Force
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Positively charged object
Negatively charged object
Neutral object
Fewer electrons than
more electrons than
same number of
protons
protons
electrons and protons
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Electric Charge: A form of charge, wither positive or negative, that exerts an electric force.
Questions
1. Which particles of an atom move most easily from one material to another? Where are
they found?
2. You rub a neutral object with a piece of wool. Some of its electrons are transferred to the
wool. Is the object now neutral, negatively charged, or positively charged? How do you
know?
3. Object A is negatively charged. It is attracted by object B. Object C is repelled by object
B. What charge does object C have? How do you know?
Static Electricity: An imbalance of electric charges on the surface of an object
Practice Questions
Page 471, Questions 2-9