Valence electrons and lewis dot structures

1. BELL RINGER
Date: October 30th 2018
Which would be the better class field trip: visiting a
volcano or visiting a glacier? Explain your choice.

3. VALENCE ELECTRONS

4. RECALL: BOHR MODEL
• A shell diagram
shows all
electrons, but we
are most
interested in the
electrons in the
outermost energy
level  called the
valence level or
valence shell.

5. VALENCE ELECTRONS
• The electrons in the outer most electron shell are
called valence electrons
• These electrons are important because they are
involved in chemical bonding.
• The shell containing electrons that is furthest from
the nucleus is called the valence shell
• Electrons not in the outermost shell are called
core electrons.

6. • Each electron shell can hold a certain number of
electrons
• Electron shells are filled from the inside out
• Noble Gases have full outer electron shells
• All other elements have partially filled outer
electron shells
VALENCE ELECTRONS

7. OCTET RULE
• Atoms bond in order to have 8 valence
electrons.
• Exceptions:
• Hydrogen and Helium only need 2 valence
electrons to be complete/stable.
• This is because they both have 1 electron
shell.
• Remember this first shell can only hold 2
electrons.

9. • How many valence electrons are in the
following atoms?
 He
 O
 Na
 Cl
Valence Electrons
= 2
= 6
= 1
=
7

10. ELECTRON DOT STRUCTURE
• Commonly known as Lewis structure
• Lewis structures consist of the element’s symbol
representing the nucleus, surrounded by dots
representing the element’s valence electrons.

11. LEWIS STRUCTURES
•Find out which group
(column) your element is in.
•This will tell you the
number of valence
electrons your element has.
•You will only draw the
valence electrons.

12. STEPS
1) Write the element symbol.
2) Carbon is in the 4th group, so it has 4
valence electrons.
3) Starting at the right, draw 4 electrons, or
dots, around the element symbol.

13. RULE
Rule #1. No side can have more than two dots.
Rule #2. When filling the sides of the element symbol
each side gets one dot before doubling up (exceptions
are hydrogen and helium)
Across Period 2:

14. ELECTRON DOT STRUCTURE
Write the electron-dot structures for the
following elements:
 Helium
 Oxygen
 Sodium
 Chlorine

15. OCTET RULE: EXTENDED
• Octet rule says that atoms like to have full
outer shells of 8 electrons.
•Atoms will try to gain or lose electrons to have
a full valence shell
• They do this by bonding with other atoms.

16. IONS
• Ions are atoms or groups
of atoms with a positive
or negative charge.
• Taking away an electron
from an atom gives a
cation with a positive
charge.
• Adding an electron to an
atom gives an anion with
a negative charge.

17. ¿ATOMS VS IONS?
• A stable atom contains the same number of
electrons as protons and no net charge.
• When electrons are added or removed, the stable
atom becomes an ion.
• If electrons are removed, the net charge of the ion
will be positive and known as a cation.
• When electrons are added, the net charge of the
ion becomes negative and known as an anion.
• To tell the difference between an atom and an ion,
look to see if there is a charge in the superscript!
• Ions: Na+ Ca+2 I- O-2
• Atoms: Na Ca I O

18. PREDICTING ION CHARGES
In general
Metals lose electrons ---> cations
 E.g: Mg
Nonmetals gain electrons ---> anions
 E.g: F

19. LEARNING CHECK –
COUNTING
State the number of protons, neutrons, and
electrons in each of these ions.
K+ O -2 Ca +2
#p+ ______ ______ _______
#no ______ ______ _______
#e- ______ ______ _______
19
20
18
8
8
10
20
20
18

20. ONE LAST LEARNING CHECK
Write the nuclear symbol form for the following
atoms or ions:
A. 4 p+, 5 n, 2 e- ___________
B. 17p+, 18n, 17e- ___________
C. 13p+, 14n, 10e- ___________
Al3
+
Cl
Be2+