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1.The ____________________________ is a weighted average that reflects the abundance of different isotopes. 2.The ______________________________ is determined by adding the number of protons and neutrons in an atom. 3.__________________________ are atoms of the same element that have different numbers of neutrons. 4.An element’s ____________________________ and the number of protons in the nucleus of its atoms are always the same.
Average atomic mass
Mass number
Isotope
Atomic Number
26
Fe Iron
55.845
Different Elements—Different Numbers of Protons
The type of
element
the number of protons
the number of electrons
What are the atomic numbers of carbon, nitrogen and oxygen? Carbon = 6, Nitrogen = 7, Oxygen = 8
Explain the difference between an oxygen atom and a carbon atom.
Oxygen has 8 protons. Carbon has 6 protons.
What are two numbers the can be used to identify
an element?
Explain the difference between a Boron atom (B) and an
Oxygen atom.
Analyze the periodic table and tell how you think it is
organized
The number of protons and electrons
Boron has 5 protons and 5 electrons
Oxygen has 8 protons and 8 electrons
Organized by increasing atomic #
1. Fluorine has an atomic number of 9.
What can you conclude about an atom of
fluorine
A) It has 9 protonsA) It has 9 protons
2. In what part of an atom can protons be found?
C) Inside the atomic nucleusC) Inside the atomic nucleus
3. Since atoms are very small, what can you infer about atomic mass units?
D) Atomic mass units and grams
Measure different properties
D) Atomic mass units and grams
Measure different properties
4. An atom of flourine has an atomic mass of 19u, Keeping in mind that its atomic number is 9, what can you infer about this atom
C) It has ten neutronsC) It has ten neutrons
5. If a sulfur atom has 16 protons, 16 electrons, and 16 neutrons, it’s atomic mass is?
B) 32B) 32
6. If a hydrogen atom has 1 proton, 1 electron, and 1 neutron it’s atomic number is?
A) 1A) 1
7. On the periodic table, how is the atomic mass represented?
A) As an average of the mass of
different isotopes
A) As an average of the mass of
different isotopes
8. What do carbon-12 and Carbon-14 have in common?
A) They have the same number of
protons
A) They have the same number of
protons
9. How is Carbon-12 different from Carbon-14?
C) They have a different number of
neutrons
C) They have a different number of
neutrons
• Atoms of the same element can have different numbers of neutrons.
• Isotopes are atoms of the same element that have different numbers of neutrons.
• Most elements have several isotopes.
Neutrons and Isotopes
Why do the isotopes of carbon in the table
have different mass numbers?
They have a different number of neutrons
• An ion is an atom that is no longer neutral because it has gained or lost electrons.
• An ion can be positively or negatively charged depending on whether it has lost or gained electrons.
Ions—Gaining or Losing Electrons
• When a neutral atom loses one or more electrons, it has more protons than electrons and as a result, has a positive charge.
• An atom with a positive charge is called a positive ion.
• When a neutral atom gains one or more electrons, it now has more electrons than protons and as a result, has a negative charge.
• An atom with a negative charge is called a negative ion.
An ion is an atom that is no longer ________________ because it has
______________________ or _____________________ electrons.
neutral
gained lost
An atom that lost
an electron
Positive Charge
An atom that gained
an electron
Negative Charge
Ions—Gaining or Losing Electrons(cont.)
How does a neutral atom change when its number of protons or electrons changes?
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