Elements combine to form
compounds
Chemical Bonds and
Compounds

Compounds have different properties
from the elements that make them

Atoms of different elements are held
together by chemical bonds

Bonds help to determine the
properties of a compound
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Properties of Compounds

Depend on atoms
in the compound

Depend on how the
atoms are
arranged in the
compound
Properties of Compounds are different
than the elements that make them

www.sciencelearn.org.nz
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Example:
• C and H combine to
form natural gas,
auto gas, waxes in
candle,
plastics…etc.
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A given compound
always contains atoms
of elements in a specific
ratio

Ammonia NH3 always
has a 1:3 ratio of
Nitrogen to Hydrogen
NaCl (salt)
• Na is a metallic solid
• Cl is a greenishgreenish-yellow gas
that is poisonous
• Table salt (NaCl) is used to
flavor and preserve foods
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Chemical Formula
Atoms combine in predictable
numbers

H2O (water)
• H and O are colorless gases
at room temperature
• Water is a liquid at room
temperature

www.uh.edu
Chemical Formula:
uses the chemical
symbols to represent
the atoms of the
elements and their
ratios in the chemical
compound. H2O 2:1
ratio of H to O
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Chemical Bonds hold Compounds
Together

Chemical bonds
are the “glue” that
holds the atoms of
elements together

Chemical bonds
form when the
electrons in the
electron clouds
interact
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www.bennett29j.k12.co.us

An elements location on the periodic table
gives a clue as to the type of ions the
atoms of that element will form

Group 1 metals (Li, Na, K…) usually lose
one electron to form positive ions.

Group 2 metals (Be, Mg, Ca…) usually
lose two electrons to form positive ions.

Group 17 nonmetals (F, Cl, Br…) gain one
electron to form ions with a 11- charge.

Group 16 nonmetals (O, S, Se…) gain two
electrons to form ions with a 22- charge.
Atoms can transfer electrons

Ions are formed when atoms gain or
lose electrons

Gaining electrons = negative charge

Losing electrons= positive charge
Ionic Bonds
Group 1

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Group 1 lose eeGroup 2 lose 2e
2e--
Group 17 gains 1 eeGroup 16 gains 2 ee-
The force of attraction between positive
and negative ions.
Particles with opposite electrical charges
attract each other

Atom from element group 1 (1+)
combines with an atom from element
group 17 (1(1-) to form an ion.

Example Na combines with Cl
• Na loses 1 electron and Cl gains the
electron
• Creating an ionic bond
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Ionic compounds

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
Names of Ionic Compounds
Ionic bonds form between all nearby
ions of opposite charge.
Ionic compounds are very stable and
their crystals are very strong.
The shape of the crystals formed
depends on the ratio of positive to
negative ions and the sizes of the
ions
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Covalent Bonds

A pair of shared electrons between
atoms.(prefix co
co-- means partner)

Neither atom gains or loses an electron
The shared electrons are attracted to both
positively charged nuclei. (nucleus has a
positive charge because of protons)
A covalent bond is represented by a line
between the two atoms
I2
I-I


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First, take the name of the positive metal
element
Second, take the name of the negative,
nonmetal element and give it an –ide
ending
Third, combine the two names
Example: BaI2
1: barium
2: Iodine…add ide…Iodide
3: barium iodide
Covalent Bond

The number of covalent bonds that
an atom can form depends on the
number of electrons that it has
available for sharing.
• Atoms of Group 16 (O,S…)can form two
covalent bonds.
• Atoms of group 15 (N,P…) can form
three bonds
• Atoms of group 14 (C, Si…)can form
four bonds
Finding Valence Electrons
Valence Electrons

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Valence electrons: are the electrons in the
outer electron cloud.
Electrons orbit in shells: 2, 8, 18, 32, 50
(Inner shell is 2, next shell has 8
electrons…)
A quick way to determine the number of
valence electrons for a representative
element is to look at which group it is in.
Elements in group 1 have 1 valence
electron.
Elements in group 2 have 2 valence

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For example:
Sodium has an Atomic Number of
11
This means an atom of Sodium
has 11 Protons
and therefore 11 electrons.
The electrons are arranged as:
• First Shell = 2,
• Second Shell = 8,
• Third Shell = 1
• (Giving a total of 11.)
(2+8+1=11)
Na has 1 valence electron and is in
group 1
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Chemical Bonds Give all Materials
their Structure

Ionic Compounds (losing/gaining ee-)
• Most have a crystal structure
• Solid at room temperature
• High melting and boiling points (takes a
lot of energy to break the bond)
• Hard, brittle, good conductors of
electricity once the ions are separated
• Dissolve easily in water
Chemical Bonds Give all Materials
their Structure

Covalent Compounds (sharing valence ee-)
• Exist as individual molecules
• Chemical bonds give each molecule a specific
three--dimensional shape
three
• Molecular shape can affect properties of the
compounds
• Melt and boil at lower temperatures (takes less
energy to break up because atoms are
organized as individual molecules)
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Metals have unique
bonds

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
Metallic bond:
bond: the equal sharing of electrons in all
directions so electrons move easily among the
atoms of the metal
Atoms can slide past one another in metallic bonds
which allows for easy shaping
Properties of metals depend on bonds
• Good conductors of electric current
• High melting point
• Solid at room temperature (except Hg)
• Easily shaped and pounded
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