Transcript Slide 1

Atoms have NO
overall charge
• ATOMS DO NOT HAVE A CHARGE BECAUSE THEY
HAVE AN EQUAL NUMBER OF PROTONS AND
ELECTRONS WHO CHARGES EXACTLY CANCEL!
• A CHLORINE ATOM HAS 17 PROTONS, WHICH
MEANS IT HAS 17 ELECTRONS ALSO…
• NEUTRONS HAVE NO CHARGE.
•BUT…if an electron is removed from an element
then things change…
Valence Electrons: an
electron in the outermost
energy level of an atom.
There can only be
2 electrons in
the first energy
level.
The second energy
level can hold 8
electrons & every
level after that.
Nitrogen’s electrons only fill up
five of the second shell. So this
means there are 5 valence
electrons for Nitrogen (the same
as the group they are found in
on the periodic table – 5A)
E
7 protons
Nitrogen (N)
7 electrons
E
E
2 e-’s
E
E
8 e-’s
E
E
8 e-’s
An octet is a set of
8. An energy level
can hold up to 8
electrons in its
outer most energy
level.
Atoms of metallic elements tend to lose
their valence electrons leaving a complete
octet in the next lowest energy level.
Atoms of some nonmetallic elements
tend to gain electrons or share electrons
with another nonmetallic element to
achieve a complete octet.
• Ionic Bonds form when elements do
not have complete sets of valence
electrons. This usually occurs
between a metal cation and a nonmetal
anion.
• Some elements achieve stable
electron configurations through the
transfer of electrons between atoms.
• Transfer of electrons takes place
when one electron is donated or
accepted from one atom to another.
• Formation of Ionic Bonds=
When an atom gains or loses an
electron it becomes an ion
• An ion is a charged
particle which can bond with
another charged particle
• A CATION is a positively
charged atom, such as Na+ or
H+ or Be2+ , etc.
• A ANION is a negatively
charged atom, such as I-, Cl-,
S2-, N3-, etc.
• Sharers, such as Carbon
usually bond covalently and
share electrons.
1. Would Lithium (Li) be a cation or anion?
Cation + 1
2. Would Hydrogen (H) be a cation or anion?
Cation +1
3. Would Nitrogen (N) be a cation or anion?
Anion 3-
4. Would Florine (F) be a cation or anion?
5. Boron?
Cation 3+
6. Aluminum?
7. Calcium?
Cation 3+
Cation 2+
Anion 1-
• The amount of energy used to
remove and electron is called
IONIZATION ENERGY
• The Trends are as follows on
the periodic table.
•Ionization: the
process of adding
electrons to or removing
electrons from an atom
or a group of atoms.
Generally increases
Generally decreases
• An electron can move to a
higher energy level when an
atom absorbs energy.
- Ionic Bonds
Properties of Ionic Compounds
• In general, ionic compounds are hard, brittle
crystals that have high melting points. When
dissolved in water or melted, they conduct
electricity.
- Ionic Bonds
Ions and Ionic Bonds
• When an atom loses an electron, it loses a
negative charge and become a positive ion.
When an atom gains an electron, it gains a
negative charge and becomes a negative ion.
Sodium (Na)
If the first energy level only has two electrons
then electrons are located in the next energy
level.
For example, Sodium
p = 11
e= 11
n= 12
After the first two electrons take up the first
energy level, 9 more electrons are located
in different energy levels.
Only 8 electrons can fill up the second
energy level. This is called the octet rule.
So the last electron is located in the last
level, all by itself! This is what gives sodium
a (+1) charge when it becomes ionized.
• When the outermost energy level
of an atom is filled with electrons,
the atom is stable and not likely to
react.
• An electron dot diagram is a
model of an atom in which each
dot represents a valence electrons.
• Atoms can bond with one
another by switching, sharing, or
exchanging electrons with one
another.
- Atoms, Bonding, and the Periodic Table
Valence Electrons and Bonding
• The number of valence electrons in an atom
of an element determines many properties of
that element, including the ways in which the
atom can bond with other atoms.
- Atoms, Bonding, and the Periodic Table
The Periodic Table
• As the number of protons (atomic number)
increases, the number of electrons also
increases. As a result, the properties of the
elements change in a regular way across a
period.
- Ionic Bonds
Ions and Ionic Bonds
• Ionic bonds form as a result of the attraction
between positive and negative ions.
Let’s Practice!
# of Valence Electrons: ______
# of Valence Electrons: ______
# of Valence Electrons: ______
Charge as an Ion: _________
Charge as an Ion: _________
Charge as an Ion: _________
# of Valence Electrons: ______
# of Valence Electrons: ______
# of Valence Electrons: ______
Charge as an Ion: _________
Charge as an Ion: _________
Charge as an Ion: _________
What is a covalent bond
• A covalent bond occurs when atoms share
electrons
• Covalent bonds occur between two nonmetals
• Valence electrons play a role in covalent bonds
Molecules and Molecular Compounds
• Molecule – a neutral group of atoms joined
together by a covalent bond.
• Diatomic molecule – a molecule consisting 2
of the same element. Example: O2
• Molecular compound – a compound
composed of molecules. (covalently bonded
atoms).
The Diatomic Elements
• The elements Hydrogen, Nitrogen, Fluorine, Oxygen,
Iodine, Chlorine, and Bromine are always found as
diatomic molecules:
• HONClFIBr (say HONKLE-fibber)
• BrINClHOF (say Brinckle-hoff)
• I Have No Bright Or Clever Friends
• There are seven such elements. The first one is the first
element Hydrogen; the rest form a 7 on the periodic
table: N, O, F across, then going down Cl, Br, I.
Characteristics of Molecular Compounds
(elements that are bonded covalently)
• Lower melting points and boiling points than
ionic compounds.
• Most are gases or liquids at room
temperature.
• Are composed of atoms of 2 or more
nonmetals.
Molecular Formulas
• A molecular formula shows how many atoms
of each element a molecule contains.
Ex: H2O has 2 hydrogen atoms and 1
oxygen atom
• You can represent a molecule by its molecular
formula, structural formula, space-filling
molecular model, perspective drawing or by a
ball-and-stick molecular model.
Different ways to represent a
molecule:
Structural formula
Perspective drawing
Molecular Formula
NH3
Space-filling molecular model
Ball-and-stick molecular model
What happens in a covalent bond
• In a covalent compound, electrons are shared between atoms
to form a covalent bond in order that each atom in the
compound has a share in the number of electrons required to
provide a stable, Noble Gas, electronic configuration (octet
rule).
• Each atom “thinks” it has a full outer shell containing 8
valence electrons
• The sharing of electrons is what makes the bond and holds
the atoms together
Lewis Structures and Covalent Bonds
• Electrons in the Lewis Structure (electron dot diagram) are
paired to show the bonding pair of electrons.
• Often the shared pair of electrons forming the covalent bond
is circled
• Sometimes the bond itself is shown with a dash (-)
• A pair of valence electrons that is not shared between atoms
is called an unshared pair, lone pair or non-bonding pair.
Water – Is an example of a covalent
compound.
• Hydrogen needs 2
electrons to fill its
outermost shell
• Oxygen needs two
electrons to fill its
outermost shell
Lewis Structure of Water (single
covalent bonds)
http://web.visionlearning.com/custom/chemistry/animations/CHE1.7-an-H2Obond.shtml
Lewis Structure of Carbon Dioxide: CO2
(Double covalent bonds)
• Carbon has four valence
electrons, and oxygen has
six.
• Each pair of shared
electrons forms a single
bond
• A bond that involves two
shared pairs of electrons
is called a double covalent
bond.
Lewis Structure of Nitrogen (triple
covalent bonds)
T
+
=
A bond formed by sharing 3 pairs of electrons is
called a triple covalent bond.
You Try It
• What would the formula be for a compound
containing carbon and fluorine
• What is the formula for a compound
containing nitrogen and oxygen
• Carbon and hydrogen?
• Antimony and bromine?
• Chlorine and oxygen?