Name________________________
Period_______
Date____________
The structure of the atom
Goal
Students will be able to determine the number of protons, electrons, and neutrons in an
atom as well as its atomic charge based on the information in the periodic table of
elements.
Information
Atoms are made-up of three tiny subatomic particles: protons, neutrons, and
electrons. The protons and neutrons are grouped together in the nucleus, which is at the
center of the atom. The chart below compares electrons, protons, and neutrons in terms of
electrical charge and mass.
Location in the
atom
Charge
Mass (g)
Mass
(amu)
Found outside
the nucleus
-1
9.109 x 10 -28
5.5 x 10-4
Proton
Found in
nucleus
+1
1.673 x 10-24
1
Neutron
Found in
nucleus
0
(neutral)
1.675 x 10-24
1
Electron
The atomic number of an element is the number of
protons in the nucleus of every atom of that element. Each
atom has a different atomic number. It is used as an
identifier of an element.
The mass number tells you the number of protons
plus the number of neutrons.
number of protons
+
number of neutrons
Mass number
Isotopes are atoms of the same element that have
different numbers of neutrons. The number of protons in all
the isotopes of an element are the same.
The atomic mass of an element is based on the mass numbers of the elements
isotopes. For example, a standard table of elements lists the element lithium as having an
atomic mass of 6.94amu. That does NOT mean there are 3 protons and 3.94 neutrons in a
lithium atom! On average, 94% of lithium atoms are lithium with a mass of 7 amu and 6%
are lithium with a mass of 6 amu. The average atomic mass of lithium is 6.94 because of
the weighted average of the mixture of isotope. Atomic mass is measured in Atomic Mass
Units (amu).
Part 1
1. What is the smallest particle by mass?
2. What is the charge of a proton?
3. What is the charge of a neutron?
4. What is the charge of an electron?
5. If you have 2 protons what is the charge?
6. If you have 1 proton and 1 neutron what is the charge?
7. If you have 1 proton and 1 electron what is the charge
8. If you have 1 proton, 1 electron and 1 neutron what is the charge?
9. The charge of an atom is neutral (zero net charge). What does that say about the
number of protons and the number of electrons in an atom?
10. Which number associated with an atom is a characteristic Property? Why?
Use the periodic table of elements to complete the table below.
What the nucleus
contains
What is the
element
Symbol
How many
electrons does
the neutral
atom have?
What is the
mass number?
Part 2
Carbon has three isotopes: carbon-12, carbon-13, and carbon-14. The atomic number of
carbon is 6. The atomic mass of carbon is 12.0111amu.
11) How many protons are in the nucleus of a carbon atom?
12) How many neutrons are in the nucleus of a carbon-13 atom?
13) Which of the carbon isotopes is most abundant in nature? How do you know?
14) Look at a periodic table. The atomic mass of hydrogen is 1.00794. Why is this number
not rounded off to 1?
15) How many protons and neutrons are in the nucleus of each isotope?
A) hydrogen-2 (atomic number = 1)
B) scandium-45 (atomic number = 21)
C) aluminum-27 (atomic number = 13)
D) uranium-235 (atomic number = 92)
E) carbon-12 (atomic number = 6)
16) By mass, how many electrons would balance
with one proton?
17) Although electrons have mass, they are not considered in determining the mass
number or atomic mass of an atom. Why?
18) A hydrogen atom has one proton, two neutrons, and no electrons. Is this atom neutrally
charged? Explain your answer.
19) An ion is an atom or group of atoms, normally electrically neutral, that has lost or
gained one or more electrons. If an atom of sodium-23 (atomic number = 11) has a
positive charge of +1. Given this information, how many electrons does it have? How
many protons and neutrons does this ion have?