Name________________________ Period_______ Date____________
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)
Electron
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
Neutron
Found in nucleus
0
(neutral)
1.675 x 10
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.
-24
The mass number tells you the number of protons plus the number of neutrons.
1
1 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) ion 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?