When a neutral atom loses or gains electrons, it is no longer neutral. It becomes an ion that has a positive or negative charge depending on whether electrons were lost or gained: - Losing electrons leaves the atom with more protons than electrons, giving it a positive charge. It is now a positive ion. - Gaining electrons leaves the atom with more electrons than protons, giving it a negative charge. It is now a negative ion. So in summary, losing or gaining electrons changes a neutral atom's charge balance between protons and electrons, making it an ion that is positively or negatively charged. The number of protons does not change, only the number of electrons.

2.
Do Now 26
Fe
Average atomic mass
1.The ____________________________ is a weighted
Iron
average that reflects the abundance of different
55.845
isotopes.
Mass number
2.The ______________________________ is determined
by adding the number of protons and neutrons in an
atom.
Isotope
3.__________________________ are atoms of the same
element that have different numbers of neutrons.
Atomic Number
4.An element’s ____________________________ and the
number of protons in the nucleus of its atoms are
always the same.

3. Different Elements—Different
Numbers of Protons
the number of protons
The type of
the number of electrons
element

4. 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.

5. What are two numbers the can be used to identify
an element?
The number of protons and electrons
Explain the difference between a Boron atom (B) and an
Oxygen atom.
Boron has 5 protons and 5 electrons
Oxygen has 8 protons and 8 electrons
Analyze the periodic table and tell how you think it is
organized
Organized by increasing atomic #

6. 1. Fluorine has an atomic number of 9.
What can you conclude about an atom of
fluorine
A) It has 9 protons
A) It has 9 protons

7. 2. In what part of an atom can protons be
found?
C) Inside the atomic nucleus
C) Inside the atomic nucleus

8. 3. Since atoms are very small, what can
you infer about atomic mass units?
D) Atomic mass units and grams
D) Atomic mass units and grams
Measure different properties
Measure different properties

9. 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 neutrons
C) It has ten neutrons

10. 5. If a sulfur atom has 16 protons, 16
electrons, and 16 neutrons, it’s atomic
mass is?
B) 32
B) 32

11. 6. If a hydrogen atom has 1 proton, 1
electron, and 1 neutron it’s atomic number
is?
A) 1
A) 1

12. 7. On the periodic table, how is the atomic
mass represented?
A) As an average of the mass of
A) As an average of the mass of
different isotopes
different isotopes

13. 8. What do carbon-12 and Carbon-14
have in common?
A) They have the same number of
A) They have the same number of
protons
protons

14. 9. How is Carbon-12 different from
Carbon-14?
C) They have a different number of
C) They have a different number of
neutrons
neutrons

15. 10.What can you conclude about
Carbon-14 from its name?
D
D

16. Neutrons and Isotopes
• 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.

17. Why do the isotopes of carbon in the table
have different mass numbers?
They have a different number of neutrons

18. Ions—Gaining or Losing Electrons
• 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.

19. • 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.

20. • 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.

21. neutral
An ion is an atom that is no longer ________________ because it
has
gained lost
______________________ or _____________________ electrons.
An atom that lost An atom that gained
an electron an electron
Positive Charge Negative Charge

22. Ions—Gaining or Losing Electrons
(cont.)
How does a neutral atom change
when its number of protons or
electrons changes?