2. Electrons in the highest occupied energy level of an
element’s atoms are called Valence electrons.
To find the number of valence electrons in an atom of a
representative element, simply look at its group number.
Each noble gas
(except He) has
eight electrons
in its highest
energy level.
2
3. Valence Electrons
The noble gases, Group 8, are the only exceptions to
the group-number rule.
Helium has two valence electrons, and all of the other
noble gases have eight.
valence electrons are usually the only electrons used in
chemical bonds.
As a general rule, only the valence electrons are shown
in electron dot structures.
Electron dot structures are diagrams that show
valence electrons as dots.
3
5. Electron Dot Diagrams
A way of keeping track of valence electrons.
How to write them
Write the symbol
Put one dot for each valence electron
Don’t pair up until they have to
5
X
6. The Electron Dot diagram for Nitrogen
Nitrogen has 5 valence
electrons.
First we write the symbol.
NThen add 1 electron at a
time to each side.
Until they are forced to pair up.
6
8. Electron Configurations for Cations
Metals lose electrons to attain noble gas
configuration.
They make positive ions.
Na 1s2
2s2
2p6
3s1
- 1 valence electron
or [Ne] 3s1
Na+
1s2
2s2
2p6
- noble gas configuration8
9. Electron Dots For Cations, e.g. Calcium
Metals will have few valence electrons
9
Ca
10. Metals will have few valence electrons
These will come off
10
Ca
Electron Dots For Cations, e.g. Calcium
11. Metals will have few valence electrons
These will come off
Forming positive ions
11
Ca2+
Electron Dots For Cations, e.g. Calcium
12. Electron Configurations for Anions
Nonmetals gain electrons to attain noble gas
configuration.
They make negative ions.
S 1s2
2s2
2p6
3s2
3p4
- 6 valence electrons
or [Ne] 3s2
3p4
S2-
1s2
2s2
2p6
3s2
3p6
- noble gas configuration.12
13. Electron Dots For Anions, e.g. Phosphorus
Nonmetals will have many valence electrons.
They will gain electrons to fill the highest level.
13
P P3-
15. Stable Electron Configurations
All atoms react to achieve noble gas
configuration
Noble gases have 2 s and 6 p electrons.
8 valence electrons
Also called the octet rule
15
Ar
16. Octet Rule
In forming compounds, atoms tend to achieve the
electron configuration of a noble gas.
An atom’s loss of valence electrons produces a cation,
or a positively charged ion.
Atoms of metals tend to lose their valence electrons,
leaving a complete octet in the next-lowest energy level.
Atoms of non metals tend to gain electrons or to share
electrons with another nonmetal to achieve a complete
octet.
16
18. Some ions formed by transition metals do not have
noble-gas electron configurations, but have pseudo
noble-gas electron configurations.
For example, Silver (Ag) forms a pseudo noble-gas
electron configuration. (4s2
4p6
4d10
)
The gain of negatively charged electrons by a neutral
atom produces an anion.
18
19. Names of ions
Cations keep the name of the metal
– Ca calcium
– Ca2+
calcium ion
Anions change ending to – ide
– Cl Chlorine - Cl1-
chloride ion
– O Oxygen - O2-
oxide ion
– N Nitrogen - N3-
nitride ion
19
20. Formation of Anions
20
Halide ionsHalide ions – the ions that are produced when atom
of chlorine and other halogens gain electrons
All halogen atoms have seven valence electrons and
need to gain only one electron to achieve the electron
configuration of a noble gas.
All halide ions (F-
, Cl-
, Br-
, and I-
) have charge of 1-
.
21. Questions
21
1. How can you determine the number of valence
electrons in an atom of a representative element?
Look up the group number of that element
2. Atoms of which elements tend to gain electrons?
Atoms of which elements tend to lose electrons?
Nonmetals – gain metals - lose
3. How do cations form? How do anions form?
Cation – atom loses valence electrons
Anion – atom gains valence electrons
23. Ionic Bonding
Anions and cations are held together by
opposite charges.
This is the bond
Ionic compounds are called salts.
Simplest ratio is called the formula unit.
The bond is formed through the transfer of
electrons.
Electrons are transferred to achieve noble gas
configuration.
23
34. Practice
Use electron dot diagrams to show how the
following elements make an ionic compound
and write the formula unit and name the
compound.
Mg and Cl
34
37. Ionic Compounds
Made up of
– a positive and negative ion
– a cation and an anion
– a metal and a nonmetal
37
38. Properties of Ionic Compounds
Crystalline structure.
A regular repeating arrangement of ions in the
solid.
Ions are strongly bonded.
Structure is rigid.
High melting points - because of strong forces
between ions.
38 Go to page: 197
39. Compounds composed of cations and anions are
called ionic compounds.
Although they are composed of ions, ionic
compounds are electrically neutral.
The electrostatic forces that hold ions
together in ionic compounds are called ionic
bonds.
Ionic compounds can conduct electric current
when melted or dissolved in water, because ions
are free to move in the solution.
39 Go to page: 198
42. Metallic Bonds & Properties
Metals are made up of closely packed cations rather
than neutral atoms.
The valence electrons of metal atoms can be modeled as a sea
of electrons. (they are mobile and can drift freely from one part
of the metal to another).
Metallic bondsMetallic bonds consists of the attraction of the free-floating
valence electrons from the positively charged metal ion.
The sea-of-electrons model explains many physical
properties of metals.
– Good conductors of electrical current because electrons can
flow freely.
– Ductile – they can be drawn into wires.
– Malleable – they can be hammered or forced into shapes.
Go to page: 201
43. Crystalline Structure of Metals
The crystalline structures of metals
can be compared to the stacking of
oranges in the grocery store to save
space.
Metals are crystalline and they are
arranged in very compact and orderly
patterns.
44. There are several closely packed arrangements that
are possible.
• body-centered cubic arrangement
• face-centered cubic arrangement
• hexagonal close-packed arrangement
Body-centered cubicBody-centered cubic
Every atom (except those on the
Surface) has eight neighbors.
Go to page: 202
45. Crystalline Structure of Metals
Face-centeredFace-centered cubic arrangement
every atom has twelve neighbors
46. Hexagonal close-packedHexagonal close-packed arrangement
every atom also have twelve neighbors. Because of
the hexagonal shape, the pattern is different from the
face-centered.
47. Alloys
Very few of the metallic items that you use every day
are pure metals. e.g: spoons.
Most of the metals you encounter are alloys
Alloys are mixtures composed of two or more
elements., at least one of which is a metal.
The most important alloys today are steels (Fe & C)
e.g: Brass (Cu & Zn) Stainless steel (Fe, Cr, C, & Ni)
Alloys properties are often superior to those of their
component elements.
Sterling silver (92.5% silver & 7.5% copper) is harder
and more durable than pure silver, but still soft enough
to be made into jewelry and tableware.
48. Bronze – 7 parts copper to 1 part tin. Bronze is
harder than copper and more easily cast.
Nonferrous (non-iron) alloys are commonly used to
make coins.
The most important alloys today are steels.
Alloys can form from their component atoms in
different ways. If the atoms of the components in an
alloy are about the same size, they can replace each
other n the crystal. (substantial alloy)(substantial alloy)
If the atomic sizes are different, the smaller atoms
can fit into the spaces between the larger atoms.
(interstitial alloy)(interstitial alloy)
Alloys
49. Questions
• How do chemists model the valence electrons in
metal atoms?
Metal cations surrounded by a sea of mobile valence
electrons.
• How can you describe the arrangement of atoms in
metals?
Atoms in metals are arranged in a compact and
orderly manner
• Why are alloys more useful than pure metals?
Their properties are often superior to their component
elements.
